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EHR Extract Information Model

Issuer: openEHR Specification Program

Release: latest

Status: TRIAL

Revision: [latest_issue]

Date: [latest_issue_date]

Keywords: EHR, Extract, openehr

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Issues: https://openehr.atlassian.net/browse/SPECPR/
Web: http://www.openehr.org/

Amendment Record

Issue Details Raiser Completed

R E L E A S E     1.0.4

2.1.2

SPECPUB-3. Re-instate inheritance from descendants of X_VERSIONED_OBJECT<T> to X_VERSIONED_OBJECT from Release 1.0.2 (lost in original UML conversion).

T Beale

25 May 2016

R E L E A S E     1.0.3

2.1.1

SPECRM-30. Correct documentation errors in EHR_EXTRACT class (remove text about generic parameters).

R Chen,
H Frankel,
T Beale

10 Oct 2015

SPECRM-24. Correct EHR Extract IM typographical errors.

P Gummer,
T Beale

SPECRM-13. Convert various fields to coded in EHR Extract.
EXTRACT_SPEC.type, EXTRACT_ACTION_REQUEST.action and EXTRACT_UPDATE_SPEC.trigger_events are converted to coded types.

H Frankel,
T Beale

2.1

SPECRM-14: Various EHR Extract model improvements:
Remove EXTRACT_SPEC.includes_directory and directory_archetype; remove EXTRACT_ENTITY_CONTENT class;
make EXTRACT_FOLDER classes the main containment structure; move X_VERSIONED_OBJECT to openEHR_extract package;
change EXTRACT.request_id to a HIER_OBJECT_ID;
change GENERIC_EXTRACT_ITEM.other_details to Hash<String, String>.

H Frankel,
T Beale

29 Jun 2011

SPECRM-6. Correct modelling inconsistency of every EXTRACT_CHAPTER being related to a single Entity.

T Beale

R E L E A S E     1.0.1

2.0

SPEC-189. Add LOCATABLE.parent. New invariant in EHR_EXTRACT.

T Beale

20 Feb 2007

SPECRM-10: Upgrade EHR_EXTRACT to Release-1.0. Major redevelopment.
Added X_VERSIONED_OBJECT, X_VERSIONED_FOLDER, X_VERSIONED_COMPOSITION, X_VERSIONED_EHR_ACCESS, X_VERSIONED_EHR_STATUS, X_VERSIONED_PARTY.

T Beale

SPEC-219: Use constants instead of literals to refer to terminology in RM.

R Chen

R E L E A S E     0.95

1.3.5

SPEC-118. Make package names lower case.

T Beale

10 Dec 2004

R E L E A S E     0.9

1.3.4

SPEC-41. Visually differentiate primitive types in openEHR documents.

D Lloyd

04 Oct 2003

1.3.3

SPEC-13. Change key class names, according to CEN ENV 13606.

S Heard, D Kalra, D Lloyd, T Beale

15 Sep 2003

1.3.2

SPEC-3, SPEC-4 (changes to versioning and LOCATABLE). MESSAGE_CONTENT now inherits from LOCATABLE.

T Beale, Z Tun

18 Mar 2003

1.3.1

Formally validated using ISE Eiffel 5.2. Revised structure of MESSAGE class to align better with CEN 13606-4. Renamed EHR_EXTRACT.hca_authorising to originator, similar to 13606.

T Beale

26 Feb 2003

1.3

Changes post CEN WG meeting Rome Feb 2003. Added attestations to X_TRANSACTION class. Significantly improved documentation of requirements, comparison to CEN 13606-4.

T Beale,
S Heard,
D Kalra,
D Lloyd

07 Feb 2003

1.2.2

Minor corrections to diagrams and class definitions.

Z Tun

08 Jan 2003

1.2.1

Added senders_reference to conform to CEN 13606-4:2000 section 7.4.

T Beale

04 Jan 2003

1.2

Rewritten and restructured as two packages.

T Beale

07 Nov 2002

1.1

Moved part of EHR_EXTRACT into MESSAGE. Allow for multilevel archetypable Folder structures.

T Beale,
D Kalra,
D Lloyd

07 Oct 2002

1.0

Taken from EHR RM.

T Beale

07 Oct 2002

Acknowledgements

The work reported in this paper has been funded in by the following organisations:

  • University College London - Centre for Health Informatics and Multi-professional Education (CHIME);

  • Ocean Informatics;

Special thanks to David Ingram, Emeritus Professor of Health Informatics at UCL, who provided a vision and collegial working environment ever since the days of GEHR (1992).

1. Preface

1.1. Purpose

This document defines the openEHR Data Types This document describes the architecture of the openEHR EHR Extract Information Model. This model formally defines the concepts of ‘extract request’, ‘extract’, various kinds of content including openEHR and non-openEHR, and a message wrapper. It covers use cases including EHR system communication, other clinical content messaging, and EHR system synchronisation, as well as providing an equivalent of the ISO 13606 EHR Extract. Model, used throughout the openEHR Reference Model.

The intended audience includes:

  • Standards bodies producing health informatics standards;

  • Academic groups using openEHR;

  • The open source healthcare community;

  • Solution vendors;

  • Medical informaticians and clinicians interested in health information.

  • Health data managers.

Prerequisite documents for reading this document include:

1.3. Status

This specification is in the TRIAL state. The development version of this document can be found at http://www.openehr.org/releases/RM/latest/ehr_extract.html.

Known omissions or questions are indicated in the text with a 'to be determined' paragraph, as follows:

TBD: (example To Be Determined paragraph)

Users are encouraged to comment on and/or advise on these paragraphs as well as the main content. Feedback should be provided either on the technical mailing list, or on the specifications issue tracker.

1.4. Conformance

Conformance of a data or software artifact to an openEHR Reference Model specification is determined by a formal test of that artifact against the relevant openEHR Implementation Technology Specification(s) (ITSs), such as an IDL interface or an XML-schema. Since ITSs are formal, automated derivations from the Reference Model, ITS conformance indicates RM conformance.

2. Requirements

2.1. Overview

This section describes the requirements that the openEHR Extract Information Model (IM) is designed to meet. Requirements are expressed in terms of a description of the assumed operational environments (which acts as a design constraint), a set of use cases, functional and security requirements. The family of use cases describe coarse-grained information import to and export from health information systems, using openEHR standardised information structures as the lingua franca. The Extract IM is neutral with respect to the communication technology used between systems: the information structures can equally be used in a web services environment or in a messaging environment, including secure email. The concrete method of communication is therefore not a factor in the scenarios described here.

2.2. Operational Environment

2.2.1. openEHR Environments

The assumed operational openEHR environment for openEHR Extracts is shown in the following figure. In this figure, a Request for "information from the records of one or more 'subjects'" is created by a Requesting system. A subject record may be a patient EHR, a Person record in a demographic system, or any other logically meaningful top-level entity. Responding system(s) reply in the form of one or more Extracts. The Request/Response interaction is enabled by a transport mechanism and possibly other services. This be be in the form of comprehensive middleware, web services, or simple point-topoint protocols such as SMTP (email) transport.

operational environment
Figure 1. Operational openEHR Environment for Extracts

Information in Responding systems is assumed to be in the following form.

  • Each such system contains one or more Subject records (e.g. EHRs); there may be records for the same Subject in more than one system.

  • Each Subject record consists of one or more Version containers, each of which contains the version history of a particular piece of content. For an EHR, distinct containers are used for persistent Compositions (e.g. "medications list", "problem list") and event Compositions (Compositions created due to patient encounters and other events in the clinical care process).

  • Each Version within a Version container corresponds to one version of the content managed by that container, in other words the state of a particular content item at some point in time when it was committed by a user.

  • Groups of Versions, each one from a different Version container within a Responding system correspond to Contributions, i.e. the openEHR notion of a "change-set". Any particular Contribution corresponds to the set of Versions committed at one time, by a particular user to a particular system.

The above relationships reveal a hierarchy of potential 1:N relationships in the information accessible to the requesting system, with Contributions forming an alternative view of the content. At each level of the hierarchy, a system of identifiers is needed, e.g. to distinguish Subjects, to distinguish Versions and so on. In some specific circumstances, some of these may be reduced to 1:1 relationships, e.g. there may be no versioning, removing the need for specific identifiers for versions of an item.

2.2.2. Non-openEHR Environments

The openEHR Extract defined in this specification can be used in non-openEHR environments, where the aim is to define messages whose content is expressed as templated archetypes. In general, not much can be assumed about the internal data architecture of such systems. For the purposes of this specification, the existence of two levels of information is assumed:

  • 'record' or equivalently 'patient' - i.e. a division of information on the basis of subject of care;

  • 'document' (Composition in openEHR), which is the coarsest grain item making up a record.

Regarding versioning in non-openEHR systems, it is assumed that some systems may support basic concepts including:

  • document version;

  • document version set - an identifier of a group of versions of the same logical item;

  • document type / schema type - an identifier of some kind of model, schema or content type of a given document;

  • document type version - the version of document type.

A typical environment in which Extracts can be used to send legacy information in archetyped form is one in which cross-enterprise communications are required, including discharge summaries and referrals. The content of such messages may be defined in terms of archetypes, and then templated in order to define the total content of the message.

2.2.3. Location of Information

In more advanced environments, there may be a health information location service which obviates the need for any knowledge on the part of the requestor about which systems contain information on a particular Subject of interest (e.g. a certain patient); in simpler environments, the requesting system may need to explicitly identify the target systems of the request. The diagram below illustrates a direct request and a request mediated by a location service.

reference environment
Figure 2. Health Information Reference Environment

This specification assumes that the EHR Request and Extract is between the Requesting system and each Responding system, even if the list of relevant Responding systems has been generated by a location service. In other words, this Extract specification does not encompass the idea of a compendium of Extracts from multiple Responding systems.

2.2.4. Granularity of Extract Data

In the figure Operational openEHR Environment for Extracts the lowest level of information shown in a Responding system is simply marked 'content'. This corresponds to top-level information structures such as Compositions, Folder trees, Parties etc in openEHR. Each such content item potentially contains a whole hierarchy of information items, only some of which is generally of interest to the Requestor. The typical database idea of a "query result" is usually expected to return only such fine-grained pieces. However, the Extract specification here only allows for a granularity of Compositions ('documents' etc), rather than fine-grained query responses which are dealt with by other means. This is because the primary use case of an Extract is to make parts of an EHR available somewhere else, rather than to intelligently query the record in situ and return the result.

2.2.5. Time

Versioned health record systems are 'bitemporal' systems, because they include two notions of time. Times mentioned in the data relate to real world events or states, such as the time of diagnosis of diabetes, or the date of discharge of a patient from a hospital. Real world time is distinquished from system time, which is the time of events in the information system itself, such as committal of Contributions. Both real world time and system time may need to be specified in a Request.

2.3. Use Cases

The following sections describe typical use cases that the Request/Extract model must satisfy.

2.3.1. Single Patient, Ad Hoc Request

A key clinical use case is the need to obtain some or all of a patient’s EHR from a remote system or systems. The request is most likely to be made due to the patient having been referred to another provider (including discharge to tertiary care), but other reasons such as falling ill while travelling will also figure.

The request might be made to an identified system, such as the system of the referring provider, or it may be made to all systems containing data on the given patient, if a health information location service is available.

The contents of the request may be specified in different ways, either by the clinician and/or the software, as follows:

  • get this patient’s entire EHR from an identified source for the first time;

  • get all changes to this patient’s EHR from specified (e.g. referring or GP) system since the last time this was done by me;

  • get persistent Compositions such as "current medications", "problem list" and "allergies and interactions";

  • get Compositions matching a specific query, such as "blood sugar level measurements during the last six months".

The meaning of time is content-dependent. For Observations in an openEHR EHR, the sample times might be specified; for an Evaluation that documents a diagnosis, times for date of onset, date of last episode, date of resolution could all be specified.

2.3.2. Multiple Patient, Batch Send

A very common requirement for pathology laboratories is to be able to send result data for tests done for a number of patients, on a periodic batch basis, to a known receiver such as a hospital, clinic or state health system. The batch send is usually seen as a "standing request" by the receiver, and may be on a periodic basis (e.g. send all the results available every hour), an "as-available" basis, or according to some other scheme. Such data are currently often sent as HL7v2, Edifact or other similar messages.

To Be Determined: patient per message? Send trigger?

To Be Determined: Extract may be sent unsolicited - i.e. no Request

2.3.3. Previous Versions and Revision Histories

In some circumstances, a request may be made for versions other than the latest of certain content. This might happen due to a study or medico-legal investigation that needs to establish what information was visible in certain systems at an earlier time. For example there may be a need to determine if the problem list, list of known allergies, and patient preferences were all compatible with the medications list at some earlier time.

As part of querying for previous versions, the revision histories of Versioned containers might be requested, in order to allow a user or software agent to determine which Versions are of interest.

2.3.4. Systematic Update and Persisted Requests

In larger healthcare delivery environments such as state and regional health services, patients are routinely treated by multiple providers, some or all of which are part of a large distributed clinical computing environment. They may visit various clinics, specialists and hospitals, each of which has its own patient record for each patient. However, there is usually a need for centralised aggregation of patient data within the overall health authority, with updating required on a routine basis.

In such situations, the general requirement is for a request for update, typically for more than one patient, to be made once, and for it to be acted upon repeatedly until further notice. Specific requirements may include:

  • periodic updates of changes since last update, with a specified period;

  • event-driven updates, whereby an update occurs when a certain event occurs in the server, e.g. "any change to the EHR", "any change to medications or allergies" and so on.

For these situations, the request can be persisted in the server. Even for one-off ad hoc requests, the requestor may require the request to be persisted in the server, so that it can be referred to simply by an identifier for later invocations.

2.3.5. Sharing of non-EHR openEHR Data

There will be a need to be able to request information from openEHR systems and services other than the EHR, such as demographics and workflow, as they are developed. One likely purpose for such requests is for import from openEHR systems into non-openEHR systems, for example from an openEHR demographics service to an existing hospital Patient Master index.

It should be possible to use the same general form of request as used for an EHR. However, instead of specifying Extracts of patient records (EHRs), the data shared in these other cases will be whichever top-level business objects are relevant for that kind of service, e.g. PARTYs for the demographic service and so on.

2.3.6. Provision of data from non-openEHR Systems

One of the major uses of an openEHR system is as a shared EHR system, aggregating data from various existing systems in a standardised form. Data from such systems may be provided in different ways, including various messaging forms (HL7, Edifact), various kinds of EMR document (CEN EN13606, HL7 CDA), and other formats that may or may not be standardised.

The developers of some such systems may decide to provide an openEHR-compatible export gateway, capable of serialising various data into openEHR structures, particularly the Composition / GENERIC_ENTRY form (see openEHR Integration IM) which is highly flexible and can accommodate most existing data formats. Types of non-openEHR systems that may supply openEHR Extracts in this fashion include pathology systems and departmental hospital systems, such as radiology, (RIS), histopathology and so on.

Extract Requests might be specified in openEHR form (i.e. according to this document) or in some other form, such as web service calls or messages; either way, the logical request is the same, i.e. which patients, which content, which versions, and the update basis. The responses must be some subset of the openEHR Extract presented in this document.

2.3.7. Patient Access to Health Data

Direct access by patients to their own health data outside of clinical encounters is a common aspiration of e-health programmes around the world. It seems clear that there will be various modes by which such access will occur, including:

  • patient carrying USB stick or other portable device containing some or all of health record;

  • access from home PC via secure web service to EHR, in a manner similar to online banking;

  • access to EHR data in the form of encrypted email attachments on home PC either sent unsolicited (e.g. a scan cc:d to patient by imaging lab) or by request of the patient;

  • access to EHR in the waiting rooms of doctors' surgeries, clinics etc via kiosks or normal PCs.

Both the USB stick and email scenarios involve asynchronous access of EHR information, and can be addressed by the EHR Extract.

In the case of a portable device, the most obvious need is for the device to act as a synchronising transport between a home PC containing a copy of patient / family EHRs, and the EHR systems at various clinics that the patient visits. To achieve this, when changes are made at either place (in the home record or in the record held at a clinic), it should be possible to copy just the required changes to the device. In openEHR terms, this corresponds to copying Contributions made since the last synchronisation.

The email attachment scenario is more likely to involve Extracts containing either information requested by the patient in a similar manner as for the ad hoc clinical requests described above (e.g. most recent test result) or laboratory information in the form of an openEHR Extract, destined for integration into an openEHR EHR. In the latter case, the information is likely to be in the form of Compositions containing GENERIC_ENTRIEs, built according to legacy archetypes, although it could equally be in "pure" openEHR form (i.e. Compositions containing proper openEHR Observations).

2.3.8. Move of Entire Record

A patient’s entire EHR may be moved permanently to another system for various reasons, due to the patient moving, a permanent transfer of care, or re-organisation of data centres in which EHRs are managed. This is known as change of custodianship of the record, and is distinct from situations in which copying and synchronisation take place.

The record is deleted (possibly after archival) from active use at the sending system. In these situations, the usual need is for an interoperable form of the complete EHR (including all previous versions) to be exported from the existing system and sent to the destination system, since in general the two systems will not have the same implementation platform, versioning model and so on. In some cases, the implementations may be identical, allowing a copy and delete operation in native representation could be used.

2.3.9. System Synchronisation

2.3.9.1. Mirroring

Two openEHR systems containing the same kind of data (i.e. EHR, demographic etc) may contain records that are intended to be logical "mirrors" (i.e. clones) of each other. In some cases, an entire system may be a clone of another, i.e. a "mirror system". Mirrored records are purely read-only, and in all cases, the mirror record or system is a slave of its source, and no local updates occur. Synchronisation is therefore always in one direction only.

To maintain the information in mirrored records, an efficient update mechanism is required. The openEHR Contribution provides the necessary semantic unit because it is the unit of change to any record in a system, it can also be used as the unit of update to the same record in a mirroring system.

2.3.9.2. The Virtual EHR

If changes are allowed to multiple systems that also systematically synchronise, a "virtual EHR" exists. This term indicates that the totality of changes taken together form a complete EHR, even if any particular instant in any given system, not all such changes are visible. The virtual EHR is the usual situation in any large-scale distributed e-health environment. Synchronisation might be on an ad hoc or systematic basis, and may or may not be bidirectional. The difference between a synchronisation request and any other kind of request is that the request is specified not in terms of a user query but in terms of bringing the record up to date, regardless of what changes that might require.

Due to the way version identification is defined in openEHR (see Common IM, change_control package), the virtual EHR is directly supported, and synchronisation is possible simply by copying Versions from one place to another and adding them to the relevant Versioned container at the receiver end. In a large health computing environment, cloning and mirroring might be used systematically to achieve a truly de-centralised system.

The defining condition of this use case is that one or more (possibly all) records in a system are maintained as perfect copies of the same records in other systems, with possible delays, depending on when and how updating occurs.

2.3.10. Communication between non-openEHR EMR/EHR systems

Since the openEHR Extract represents a generic, open standardised specification for representing clinical information, there is no reason why it cannot be used for systems that not otherwise implement openEHR. In this case, the Extract content is most likely to consist of Compositions and Generic_entries, and may or may not contain versioning information, depending on whether versioning is supported in the generating systems.

2.4. Technical Requirements

2.4.1. Specification of Content

Content is specifiable in terms of matching criteria. This can take two forms: lists of specific top-level content items, or queries that specify top-level items in terms of matching subparts.

To Be Continued:

Queries are expressed in the Archetype Query Language.

To Be Continued:

2.4.2. Specification of Versions

The openEHR Extract supports detailed access to the versioned view of data. Which versions of the content should be returned can be specified in a number of ways:

  • as a version time of the source EHR at which all content should be taken

  • in more specific terms, such as:

    • time window of committal;

    • with or without revision history, or revision history only;

    • all, some, latest versions of each content item;

  • in terms of identified Contributions, Contributions since a certain time etc.

To Be Continued:

2.4.3. Completeness of Data

Information transferred in an EHR Extract needs to be self-standing in the clinical sense, i.e. it can be understood by the requestor without assuming any other means of access to the responding system. In general, this means that for references of any kind in the transferred EHR data, the Extract needs to either contain the reference target, or else it must be reasonable to assume that the requestor has independent access, or else doesn’t need it.

2.4.3.1. References to Other Parts of the Same EHR

In openEHR, there are two kinds of cross reference within an EHR: LINKs (defined in LOCATABLE), and hyperlinks (DV_TEXT.hyperlink). Both of these use a DV_EHR_URI instance to represent the link target. The contents of the URI are defined in the Architecture Overview.

To Be Continued: Are EHR ids always included in URIs?

In some cases, referenced items within the same EHR will need to travel with the originally requested item, in order for the latter to make sense. For example, a discharge summary or referral might refer (via LINKs) to other Compositions in the EHR, such as Medication list, Problem list, and lab reports. On the other hand, there may be links within the requested item to objects that are not required to be sent in an Extract.

Which links should be followed when building an Extract can be specified in terms of:

  • link depth to follow, i.e. how many jumps to continue from the original item; a value of 0 means "don’t follow any links".

In addition, for LINK instances, the following can be specified:

  • link type to follow, i.e. only follow links whose type attribute matches the specification.

2.4.3.2. References to Other EHRs

References to items in other EHRs may occur within an EHR, e.g. to the EHR of a parent, other relation, organ donor etc. There is no requirement for such links to be followed when constructing EHR Extracts.

2.4.3.3. References to Resources Outside the EHR

Computable references can also be made to external items from within an openEHR EHR. Instances of the data type DV_URI occurring either on their own or in a DV_TEXT hyperlink are typically used to refer to resources such as online guidelines and references. Instances of DV_MULTIMEDIA can contain DV_URI instances that refer to multimedia resources usually within the same provider enterprise, e.g. radiology images stored in a PACS. Since URIs are by definition globally unique, they remain semantically valid no matter where the data containing them moves. However, there is no guarantee that they can always be resolved, as in the case of a URI referring to a PACS image in one provider environment when transferred to another. This is unlikely to be a problem since images are usually represented in the EHR as a small (e.g. 200kb) JPG or similar, and it is almost never the intention to have original image sets (which may be hundreds of Mb) travel with an EHR. Requests to access original images would be made separately to a request for EHR Extracts.

2.4.3.4. References to Demographic Entities

Two kinds of demographic entities are referred to throughout an openEHR EHR. Individual providers and provider institutions are referenced from PARTY_PROXY objects in the record, via the external_ref attribute, which contains references to objects within a demographic repository, such as an openEHR demographic repository, a hospital MPI or a regional or national identity service. The PARTY_IDENTIFIED subtype of PARTY_PROXY can in addition carry human readable names and other computational identifiers for the provider in question.

The second kind of demographic reference, found in the PARTY_SELF subtype of PARTY_PROXY, is to the EHR subject (i.e. patient), and may or may not be present in the EHR, depending on the level of security in place. Where it is present, it is to a record in a demographic or identity system.

For the contents of an EHR Extract to make sense to the receiver, referenced demographic items may have to be included in the Extract, if the receiver has no access to a demographic system containing the entities. Whether patient demographics are included is a separate matter, since the requestor system already knows who the patient is, and may or may not need them. The requestor should therefore be able to specify whether the Extract includes referenced demographic entities other than the subject, and independently, whether subject demographics should be included.

2.4.3.5. Archetypes and Terminology

Another kind of "reference" is terminology codes, stored in instances of the data type DV_TEXT (via the mapping attribute) and DV_CODED_TEXT.defining_code. In openEHR systems, all coded terms (i.e. instances of DV_CODED_TEXT) carry the text value of the code, in the language of the locale of the EHR. For normal use, this is typically sufficient. However, for the purposes of decision support or other applications requiring inferencing, the terminology itself needs to be available. This specification assumes that where the requestor requires inferencing or other terminology capabilities, independent access to the complete terminology will be obtained.

The same assumption is made with respect to archetypes whose identifiers are mentioned in the EHR data or meta-data: archetypes are not themselves included in Extracts, and have to be resolved separately.

2.4.4. Security and Privacy

Security becomes one of the most important requirements for the EHR Extract for the obvious reason of its exposure in potentially uncontrolled environments outside the (supposedly) secure boundaries of requesting or responding systems. The general requirement is that the contents of an Extract are based on:

  • the access control rules defined in the EHR_ACCESS object at source;

  • any other access rules defined in policy services or other places;

  • authentication of the requesting user.

Digital signing should be used based on the (preferably certified) public key of the requestor. Notarisation might also be used to provide non-repudiable proof of sending and/or receiving Extracts, although this is outside the scope of this specification.

2.4.5. Update Basis

In addition to specifying the content a basis for update also needs to be specified. The simplest possible case is that of an ad hoc one-off query. More complex cases are periodic update and event-driven update.

2.4.5.1. Persistent Request

To Be Continued:

3. Design Overview

3.1. Abstract Communication Model

The openEHR Extract model uses two design ideas. Firstly, the notion of a Request and an Extract (the reply) are distinguished. Extracts may include a copy of the Request to which the Extract is a reply, indicating what is actually in the Extract, which may differ from what was requested. Secondly, the common semantics of Requests and Extracts are modelled in a generic way, with a number of specialised Request and Extract types being based on the common classes. Different concrete types of Extract are thus used to satisfy particular groups of requirements, rather than trying to make one kind of Extract perform all possible tasks. The figure below illustrates key Extract communication scenarios, along with the various concrete Extract types defined by the model.

use cases
Figure 3. Use cases for openEHR Extracts

The EHR Extract is just one concrete type of Extract. The other types include:

  • Generic Extract: an Extract type designed for use with non-openEHR systems communicating to openEHR systems, and users of the ISO 13606 Extract specification. The Generic Extract assumes the absolute minimum about what is in a system, while remaining within the openEHR type system;

  • Synchronisation Extract: an Extract used for updating mirrored EHRs across systems; uses Contributions as the grouping concept.

Other types of Extract may be defined in the future.

The pattern of requests and replies may be controlled in time. The simplest situation is single request, single reply. Other variants include:

  • send request, persist in server, and use 'action' requests to obtain an Extract, which may have differing content each time;

  • send request indicating a repeat period, at which server automatically sends replies;

  • send request indicating a trigger event on which server should send replies.

3.2. Content Model & Representation

The general situation of any environment from which content needs to be extracted and sent to another system is that three categories of data may be needed: the 'key' clinical and administrative information, typically EHR content (e.g. patient blood pressure history); demographic information (indicating who the patient and professionals are that are mentioned in the clinical information; and relevant meta-data. These types of information almost always reside in different parts of the source system environment, but need to be combined within the Extract. The model defined in this specification allows for content to be flexibly aggregated in an Extract. The model therefore consists of a generic Extract containment structure into which specific archetyped content can be plugged, with the whole structure being templated. Each such template corresponds to one extract type, i.e. one message type. This is visualised in the figure below.

extract archetyping
Figure 4. Archetyping of Extracts

The templates can be used to generate content in at least two ways. The default approach is to use the template for a given extract type, say 'referral', to create standard openEHR content according to the published openEHR EHR Extract schema (which largely re-uses the main openEHR EHR and demographic schemas). In this approach, every Extract message conforms to the standard schema - an XML Extract document is 'standard generic openEHR XML' in this case.

An alternative approach converts each template into its own schema, to which all instances of that template conform. Different templates, e.g. discharge summaries and referrals define distinct schemas. In this method, the XML of any message is specific to its own schema. If changes are required in the message content, the schema usually has to be re-generated. The two methods are illustrated in the following figure.

representation options
Figure 5. Representation options

Which method is used depends on the requirements of the environment and other factors, such as the stability of the template structures. The sections of this document describing specific kinds of extract show details of the concrete data representations involved.

3.3. Package Structure

The rm.extract package defines the semantics of Extracts from openEHR data sources, including EHRs. The UML diagram below illustrates the package structure of the rm.extract package.

RM ehr extract packages
Figure 6. rm.ehr_extract package

The sub-packages are as follows:

  • common: semantics common to all Extracts;

  • ehr_extract: semantics for the EHR Extract type;

  • generic_extract: defines semantics of the Generic Extract type;

  • synchronisation_extract: defines semantics of the Synchronisation Extract type;

  • message: simple model of a message containing an Extract.

4. Extract.common Package

4.1. Overview

The rm.extract.common package defines the semantics common to all kinds of Extract requests and Extracts. Requests and Extracts can be implemented as messages, or used as types in a webservice environment. In the latter, the Extract request semantics would most likely be replaced by equivalent service function definitions.

The Request contains a detailed specification of the repository content required in the Extract. A Request is not always needed, and an Extract may be sent unsolicited. Requests can be made persistent and/or event-driven, supporting various periodic and continuous update scenarios. Each request may specify the data from one or more entities, e.g. EHRs or subjects.

The Extract reply may optionally include a copy of the request. Its main content is in the form of chapters, under which folders and content items contain the requested content, or as much of it as was possible to retrieve. Specific types of content item, including openEHR content, generic EMR content, and demographic content are defined in various sub-packages, How the content is arranged within folders in each chapter, and across chapters is managed by the use of archetypes and templates for the Extract/chapter structure. The following uML diagram illustrates the rm.extract.common package.

RM ehr extract.common
Figure 7. rm.extract.common Package

The typical instance structure of the EXTRACT_REQUEST and EXTRACT types is illustrated below.

abstract request extract
Figure 8. Abstract Request and Extract structure

4.2. Design

4.2.1. Extract Request

The EXTRACT_REQUEST class consists of an update_spec specifying rules for update (one-off, periodic, event-driven etc), and an extract_spec, indicating what information from the target repository is required. The latter consists of an optional version_spec, indicating which versions (default is latest) and a manifest, specifying which entities (records or subjects, and optionally which items from those entities should be included.

4.2.1.1. Content Criteria Specification

The extract_spec part of the Request applies to all content in the Extract. The attributes are as follows:

  • extract_type: what kind of Extract this is, e.g. |openehr-ehr|, |openehr-demographic|, |openehr-synchronisation|, |openehr-generic|, |generic-emr|, etc;

  • include_multimedia: a flag indicating whether inline binary objects are included or not;

  • link_depth: value indicating how many levels of link to follow when constructing the content of the Extract; the default is 0, meaning 'don’t follow';

  • criteria: specifyies queries defining the required content of each entity record;

  • other_details: an archetypable structure including further extract details.

The criteria attribute defines in the form of generic queries (i.e. queries that apply sensibly to any record) which items are to be retrieved from each entity’s record. Each query is expressed as a DV_PARSABLE instance, enabling any formalism to be used. The openEHR archetype query formalisms (AQL) could be used for example. Query expressions use variables such as $ehr to mean the current EHR from the manifest list. Queries may be as simple as the following:

SELECT * FROM $ehr              -- get all items in the record
SELECT /ehr_access FROM $ehr    -- retrieve the EHR_ACCESS object in an EHR
SELECT /ehr_status FROM $ehr    -- retrieve the EHR_STATUS object in an EHR

More sophisticated queries can be used to obtain items corresponding to a specific criteria, e.g.:

SELECT ....     -- retrieve last 6 months' worth of blood glucose measurements
...             -- retrieve ongoing medications list
......          -- retrieve items relating to active pregnancy
.....           -- retrieve all GP encounter notes since 12-03-2005

To Be Continued:

4.2.1.2. Update Specification

The update_spec part of the Request specifies how the Request is to be processed by the server. The default situation, requiring no update_spec at all, is a one-off request. Other alternatives include:

  • repeat Request with a defined period and/or trigger events;

  • persisting the Request in the server so that the requestor can make later repeat requests by referring to a previously stored request by its identifier.

An ad hoc repeat of a request persisted earlier is made using an EXTRACT_ACTION_REQUEST with action set to |repeat|. This specifies only the identifier of a request previously specified using an EXTRACT_REQUEST. Since requests are uniquely identified for all time, there can be no error in the identification.

4.2.1.3. The Manifest

The manifest specifies the scope of records to be retrieved in an Extract. In the simplest case, only a single entity (e.g. patient) and no specific items will be identified (the content will be determined by the criteria in the EXTRACT_SPEC object); this will be used in the vast majority of single-patient request scenarios. However, some scenarios will be of a batch update nature, including pathology lab result update and situations where patient records are requested corresponding to a list of referrals received by a hospital since the last such update. In these cases, the request manifest may identify a number of entities (i.e. records or patients), each of which will be allocated a separate chapter in the resulting Extract.

The item_list of each entity manifest identifies individual items using OBJECT_REF instances each containing the HIER_OBJECT_ID identifier of a particular top-level object such as a Composition, or Party. This mechanism for identifying contents of an Extract is only expected to be used when a specific identifier is known, rather than when items corresponding to filtering criteria are requested. The latter are specified using the criteria attribute.

4.2.1.4. Version Specification

An Extract request in its simplest form has no version specification, corresponding to the assumption of 'latest available version' for each matched item. However, in some situations there is a need to rettrieve previous versions, or information about versions. The version specification part of the Extract request allows this to be done. The possibilities available are as follows.

  • include_all_versions: the whole version 'stack' of each item matched by the manifest and retrieval criteria should be returned. Note that the result of this will be all available versions from the repository in question, which is in general not the same as all versions that have ever been created, since versions in the same logical version tree may exist at other repositories due to local modifications that have not been propagated to the target repository of the Extract Request.

  • include_revision_history: this flag indicates whether the revision_history of a VERSIONED_OBJECT is to be included in the Extract form of the version

4.2.2. Extract

4.2.2.1. Content Specification

The EXTRACT consists of a request_id, an optional participations list, an optional specification and a set of chapters, containing the retrieved content. The participations attribute denotes parties that were responsible for creating the Extract. The specification takes the same form as the extract_spec of the EXTRACT_REQUEST, but in an EXTRACT instance, indicates the actual contents of the Extract. This will usually differ in from the request specification in that it will list in the manifest section the actual entities (and the identifiers they are known by in the receiver system) retrieved, whereas the request may not specify any entities (it may rely on query criteria), or it may specify a different set of entities than were retrievable in the receiver system.

4.2.2.2. Content

The content of an Extract is contained within the chapters attribute, in the form of one of more instances of the EXTRACT_CHAPTER class or its subtype EXTRACT_ENTITY_CHAPTER. Within an EXTRACT_CHAPTER the content attribute contains a folder structure made of EXTRACT_FOLDER objects which in turn contain the content items. The folder structure is defined by archetypes, and can be used to separate the parts of a health record, or group items according to some other scheme e.g. episode. A specific kind of chapter, the EXTRACT_ENTITY_CHAPTER, is used to carry content associated with a single entity, i.e. patient. This means that an Extract may contain data relating to multiple entities, i.e. multiple patients.

The EXTRACT_CONTENT_ITEM class is subtyped in later sections of this specification to define metadata for specific kinds of content.

4.2.3. Participations and Demographic Referencing

A key difference between an 'extract' or in fact any kind of message carrying information out of a system environment is that the Extract combines in one place information typically found in multiple services in the original environment. Two kinds of information routinely included in Extracts are clinical (i.e. EHR / EMR or similar) and demographic data regarding participations of the subject and other parties in the activities documented in the clinical information.

Within the openEHR EHR model, a 'participation' is defined by the PARTICIPATION class in the rm.common.generic package. Actual participation instances include a performer object (a subtype of PARTY_PROXY), and optionally an external reference object (type PARTY_REF). The latter contains a reference to the demographic entity within a demographic service, provider registry or similar. Within the Extract, participations occur in two places. In the EHR_EXTRACT class, participations are used to provide information about parties related to the Extract. These are created new with each Extract (i.e. they are not EHR data that is part of the Extract content. Accordingly, a simplified form of the PARTICIPATION class is used: EXTRACT_PARTICIPATION. The only difference is that the performer reference is a simple string, allowing it to contain a GUID reference to a demographic party included elsewhere in the same Extract.

Participations also occur in the actual content of the EHR, and in this case, they original structures are copied faithfully, including any in-line performer information. If there was an external_ref present, pointing to a demographic entity that is also to be included in the Extract, this reference is rewritten to point to a local copy of the demographic entity (using a GUID), within the Entity chapter of the Extract.

The result of this is that for source data whose original external references are to external demographic entities, the logical structure is completely preserved within the Extract, with just the reference being rewritten to the GUID values used in the Extract (which may well come from the original demographic database or service).

A typical arrangement is to dedicate a single chapter to all demographic entities referenced within the Extract, optionally with an internal Folder structure. Some example arrangements are illustrated in the EHR and generic Extract sections below.

4.3. Class Descriptions

4.3.1. EXTRACT_REQUEST Class

Class

EXTRACT_REQUEST

Description

Generic model of a Request for an Extract, containing an Extract specification.

Inherit

LOCATABLE

Attributes

Signature

Meaning

1..1

extract_spec: EXTRACT_SPEC

Specification details of the request.

0..1

update_spec: EXTRACT_UPDATE_SPEC

Update details of the request.

1..1
(redefined)

uid: HIER_OBJECT_ID

Identifier of this Request, generated by requestor.

4.3.2. EXTRACT_ACTION_REQUEST Class

Class

EXTRACT_ACTION_REQUEST

Description

Generic model of a Request for an Extract, containing an Extract specification.

Inherit

LOCATABLE

Attributes

Signature

Meaning

1..1

request_id: OBJECT_REF

Identifier of previous EXTRACT_REQUEST.

1..1

action: DV_CODED_TEXT

Requested action: cancel | resend | send new. Coded by openEHR Terminology group "extract action type".

1..1
(redefined)

uid: HIER_OBJECT_ID

4.3.3. EXTRACT_SPEC Class

Class

EXTRACT_SPEC

Description

Specification of an Extract’s contents. Subtypes can be used to add details specific to the type of Extract. The specification consists of attributes specifying the directory, and two further groups of attributes in their own classes, namely a version specfication (which versions of information items are to be included) and a manifest (which entities are to be included in the extract).

Use: Used in a request to specify an Extract, as well as to describe what is contained in an Extract.

Attributes

Signature

Meaning

0..1

version_spec: EXTRACT_VERSION_SPEC

Specification of which versions of information items to include in the Extract. If Void, the default is latest versions only (which is reasonable for non-versioning systems as well).

1..1

manifest: EXTRACT_MANIFEST

Specification of entities (e.g. records) to include in the Extract.

1..1

extract_type: DV_CODED_TEXT

Coded term indicating the type of content required, e.g.

  • openehr-ehr

  • openehr-demographic

  • generic-emr

  • other

Coded by openEHR Terminology group "extract content type".

1..1

include_multimedia: Boolean

Indicates whether inline instances of DV_MULTIMEDIA in the source data are included or not.

1..1

priority: Integer

Requested priority of this request to be handled by server. Priority schemes are likely to be local, and use values agreed by both ends.

TBD: alternative is standard coded terms

1..1

link_depth: Integer

Degree of links to follow emanating from content items specified for inclusion. The kind of links to follow is dependent on the type of Extract.

All items at the target end of followed links at the given depth are also included in the extract; EXTRACT_CONTENT_ITEM.is_primary is used to differentiate. - 0 = don’t follow; - 1 = follow first degree links; - 2 = follow 2nd degree links; - …​. - n = follow nth degree links

0..1

criteria: List<DV_PARSABLE>

Queries specifying the contents of this Extract.

0..1

other_details: ITEM_STRUCTURE

Other specification items. Archetypable.

4.3.4. EXTRACT_MANIFEST Class

Class

EXTRACT_MANIFEST

Description

Specification of the candidate entities and optionally top-level items (e.g. Compositions) to be included in the Extract.

Attributes

Signature

Meaning

1..1

entities: List<EXTRACT_ENTITY_MANIFEST>

List of entity manifests uids of items included in the Extract; for openEHR data, these are uids identifying the version containers.

4.3.5. EXTRACT_ENTITY_MANIFEST Class

Class

EXTRACT_ENTITY_MANIFEST

Description

The manifest for one entity (e.g. EHR subject), identifying the entity and optionally specifying top-level items to be included in the Extract. The list actually included may be modified by the version_spec part of the specification, and also by the link_depth attribute. In repeat (standing order) requests, the final inclusion may be modified by the send_changes_only value for EXTRACT_UPDATE_SPEC.update_method.

Various identifiers may be provided for the entity; these are to be used by the receiver system to locate the entity. The extract_id_key attribute is used to record the identifier that will be used throughout the Extract for this entity, including in instances of EXTRACT_ENTITY_IDENTIFIER.

Attributes

Signature

Meaning

1..1

extract_id_key: String

Identifier by which this entity is known in the Extract. May be one of the other identifiers, e.g. ehr_id or subject_id, or it may be something else, including a simple integer.

0..1

ehr_id: String

EHR / EMR identifier for the entity at the target system.

0..1

subject_id: String

Subject (i.e. patient or similar) identifier for the entity at the target system.

0..1

other_ids: List<String>

Other identifiers that may be used to find the entity at the target system, keyed by type. May include medicare numbers, drivers license number, tax number etc.

0..1

item_list: List<OBJECT_REF>

List of uids of items to be included in the Extract, in cases where individual items are being requested by id. More typically, this attribute is not used, and the EXTRACT_SPEC.criteria query defines the Extract contents. If set, for openEHR data, these are uids identifying the version containers.

4.3.6. EXTRACT_VERSION_SPEC Class

Class

EXTRACT_VERSION_SPEC

Description

Specification of what versions should be included in an Extract. By default, only latest versions are included in the Extract, in which case this part of the Extract specification is not needed at all. The attributes include_all_versions and commit_time_interval are used to modify this; the former forces all versions to be included; the latter limits the versions to be those latest versions committed in the time interval, or if include_all_versions is True, all versions committed in the time interval.

Attributes

Signature

Meaning

1..1

include_all_versions: Boolean

True if all versions of each item in the Extract are included.

0..1

commit_time_interval: DV_INTERVAL<DV_DATE_TIME>

Specifies commit time interval of items to source repository to include in Extract. By default, only latest versions whose commit times fall in the range are included. If include_all_versions is True, then the range includes all versions committed within the interval.

1..1

include_revision_history: Boolean

True if revision histories of the items in the Extract are included. If included, it is always the full revision history.

1..1

include_data: Boolean

True if the data of items matched by the content spec should be included. This is the default. If False, only revision history is included in serialised versions. Turning this option on in openEHR systems causes X_VERSIONED_OBJECTs to have revision_history set, but versions Void. Useful for interrogating a server without having to look at any content data. In other systems it may or may not have a sensible meaning.

Invariants

Includes_revision_history_valid: not include_data implies include_revision_history

4.3.7. EXTRACT_UPDATE_SPEC Class

Class

EXTRACT_UPDATE_SPEC

Description

Specification of the how the request should be processed by server. The request can be persisted in the server, meaning that a) it can be re-activated by the requesting system simply by indicating Request id, and b) that a changes-only pattern of Extract updates can be set up. To achieve this, the server has to remember what was sent in the previous response.

The update mode may be event-driven and periodic update or a mixture of both. The candidate items to be sent each time are the result of re-evaluating the content and versioning parts of the specification; what is actually sent is determined by the send_changes_only flag.

Attributes

Signature

Meaning

1..1

persist_in_server: Boolean

If True, this Request is persisted in the server until further notice.

0..1

repeat_period: DV_DURATION

Period for resending update Extracts in response to original Request.

0..1

trigger_events: List<DV_CODED_TEXT>

Set of Event names that will cause sending of update Extracts. Event types include:

  • any_change - any change in content items matched by content specification, e.g. new versions of persistent compositions. If the content list allows matching of any, or a wide range of archetypes, this event type will match any additions to the record.

  • correction - match error corrections only, including deletions.

  • update - match updates (i.e. new versions) of included content items.

Coded by openEHR Terminology group "extract update trigger event type".

1..1

update_method: CODE_PHRASE

Indicate mode of update. Can be: send only items that are changed (including logical deletions) or new since last send. For persist_in_server Requests only.

Invariants

Overall_validity: repeat_period /= Void or trigger_events /= Void

Trigger_events_validity: trigger_events /= Void implies not trigger_events.is_empty

Send_changes_only_validity: send_changes_only implies persist_in_server

4.3.8. EXTRACT Class

Class

EXTRACT

Description

Generic model of an Extract of some information from a repository.

Inherit

LOCATABLE

Attributes

Signature

Meaning

0..1

chapters: List<EXTRACT_CHAPTER>

The content extracted and serialised from the source repository for this Extract.

0..1

specification: EXTRACT_SPEC

The specification that this Extract actually conforms to; might not be identical with the specification of the corresponding request.

0..1

request_id: HIER_OBJECT_ID

Reference to causing Request, if any.

1..1

time_created: DV_DATE_TIME

Creation time of this Extract

1..1

system_id: HIER_OBJECT_ID

Identifier of creating system.

1..1

sequence_nr: Integer

Number of this Extract response in sequence of responses to Extract request identified by request_id. If this is the sole response, or there was no request, value is 1.

0..1

participations: List<EXTRACT_PARTICIPATION>

Participations relevant to the creation of this Extract.

Invariants

Sequence_nr_valid: sequence_nr >= 1

4.3.9. EXTRACT_CHAPTER Class

Class

EXTRACT_CHAPTER

Description

One content chapter of an Extract; contains information relating to only one entity.

Inherit

LOCATABLE

Attributes

Signature

Meaning

0..1

items: List<EXTRACT_ITEM>

The information content of this chapter.

4.3.10. EXTRACT_ENTITY_CHAPTER Class

Class

EXTRACT_ENTITY_CHAPTER

Description

Type of chapter that contains information relating to a single demographic entity.

Inherit

EXTRACT_CHAPTER

Attributes

Signature

Meaning

1..1

extract_id_key: String

Reference to entity, usually a demographic entity such as a patient that the content of this chapter relates to.

4.3.11. EXTRACT_ITEM Class

Class

EXTRACT_ITEM (abstract)

Description

Abstract parent of Extract Folder and Content types.

Inherit

LOCATABLE

4.3.12. EXTRACT_FOLDER Class

Class

EXTRACT_FOLDER

Description

Folder in local Folder structure in an Extract. Empty Folders are allowed.

Inherit

EXTRACT_ITEM

Attributes

Signature

Meaning

0..1

items: List<EXTRACT_ITEM>

List of Folders and content items in this Folder.

4.3.13. EXTRACT_CONTENT_ITEM Class

Class

EXTRACT_CONTENT_ITEM (abstract)

Description

Abstract model of a wrapper for one content item in an Extract, containing various meta-data. Indicates whether it was part of the primary set and what its original path was. Intended to be subtyped for wrappers of specific types of content.

Inherit

EXTRACT_ITEM

Attributes

Signature

Meaning

1..1

is_primary: Boolean

True if the content item carried in this container was part of the primary set for the Extract, i.e. not added due to link-following.

0..1

is_changed: Boolean

True if the content item carried in this container is any kind of change since last send, in repeat sending situations.

0..1

is_masked: Boolean

True if the content of this item has not been included due to insufficient access rights of requestor.

0..1

item: Any

Content object.

Invariants

Item_validity: is_masked xor item /= Void

4.3.14. EXTRACT_PARTICIPATION Class

Class

EXTRACT_PARTICIPATION

Description

Model of a participation of a Party (any Actor or Role) in an activity. Used to represent any participation of a Party in some activity, which is not explicitly in the model, e.g. assisting nurse. Can be used to record past or future participations.

Should not be used in place of more permanent relationships between demographic entities.

Attributes

Signature

Meaning

0..1

time: DV_INTERVAL<DV_DATE_TIME>

The time interval during which the participation took place, if it is used in an observational context (i.e. recording facts about the past); or the intended time interval of the participation when used in future contexts, such as EHR Instructions.

1..1

function: DV_TEXT

The function of the Party in this participation (note that a given party might participate in more than one way in a particular activity). This attribute should be coded, but cannot be limited to the HL7v3:ParticipationFunction vocabulary, since it is too limited and hospital-oriented.

0..1

mode: DV_CODED_TEXT

The mode of the performer / activity interaction, e.g. present, by telephone, by email etc.

1..1

performer: String

Uid of demographic entity within Extract who performed this participation.

Invariants

Function_valid: function /= Void and then function.generating_type.is_equal (“DV_CODED_TEXT”) implies terminology (Terminology_id_openehr).has_code_for_group_id (Group_id_participation_function, function.defining_code)

Mode_valid: mode /= Void and terminology (Terminology_id_openehr).has_code_for_group_id (Group_id_participation_mode, mode.defining_code)

5. The openehr_extract Package

5.1. Overview

The rm.extract.openehr_extract package defines an openEHR-specific variant of an EXTRACT_ITEM, which consists of a form of the VERSIONED_OBJECT<T> class from the rm.common. change_control package suitable for use in Extracts. The Extract form of the class is X_VERSIONED_OBJECT<T>, and consists of attributes which replicate functional values from the EHR form of the class. This class is further subtyped via binding to non-generic types corresponding to the top-level object types of the openEHR EHR.

The UML diagram below illustrates the rm.extract.openehr_extract package.

RM ehr extract.openehr extract
Figure 9. rm.extract.openehr_extract Package

The following figure illustrates a typical instance structure of an EHR Extract.

typical extract structure
Figure 10. Typical EHR Extract structure

5.2. Design

5.2.1. openEHR Extract Item

Items from an openEHR sytem included in an EHR Extract are always top-level objects (Composition, Directory, EHR_EXTRACT, PARTY, etc, and descendants) are expressed in the serialisable form of descendants of X_VERSIONED_OBJECT<T>. This type provides a standard interoperable way to serialise all or part of VERSIONED_OBJECTs for lossless transmission between systems, regardless of the likely implementation differences in versioning at each end. Accordingly, X_VERSIONED_OBJECT turns most functional properties of VERSIONED_OBJECT into data attributes. The two attributes of most interest are revision_history, which enables the optional inclusion of the complete revision history from the original VERSIONED_OBJECT, and versions, which allows any or all of the versions to be included form the original. The revision history can be requested on its own using by setting the includes_data flag of the version specification to False.

In most scenarios, versions will be included, and revision_history excluded. Each item in X_VERSIONED_OBJECT.versions consists of a wrapped copy of an ORIGINAL_VERSION from the corresponding VERSIONED_OBJECT object in the source system.

5.2.2. EHR Extract Structure

The overall structure of the openEHR EHR for a subject can be replicated with an archetyped Folder structure that creates the groupings of directory, compositions, ehr_access, and ehr_status that are found in an openEHR EHR. This use of folders is not mandatory, but is likely to be useful in most cases, and is the structure shown in the figure Typical EHR Extract structure above.

5.2.3. Demographic Referencing

Within the content an EHR Extract, wherever PARTICIPATION and PARTY_PROXY structures occur (for the latter, the PARTY_SELF and PARTY_IDENTIFIED descendants), they are preserved intact, for reasons of fidelity. However, the final 'pointer', i.e. the OBJECT_ID.value may be rewritten within the Extract to correctly refer to the intended demographic. A typical S_PARTICIPATION structure is illustrated at the bottom of the figure Typical EHR Extract structure. In this figure, the OBJECT_ID.value has been rewritten to refer to the uid (11111111) of the first OPENEHR_CONTENT_ITEM object shown in the figure.

5.3. Class Descriptions

5.3.1. OPENEHR_CONTENT_ITEM Class

Class

OPENEHR_CONTENT_ITEM

Description

Form of EHR EXTRACT_ITEM containing openEHR serialised VERSIONED_OBJECTs.

Inherit

EXTRACT_CONTENT_ITEM

Attributes

Signature

Meaning

0..1
(redefined)

item: X_VERSIONED_OBJECT

Content object.

5.3.2. X_VERSIONED_OBJECT Class

Class

X_VERSIONED_OBJECT

Description

Variety of Extract content that consists is a sharable data-oriented version of VERSIONED_OBJECT<T>.

Attributes

Signature

Meaning

1..1

uid: HIER_OBJECT_ID

Uid of original VERSIONED_OBJECT.

1..1

owner_id: OBJECT_REF

Owner_id from original VERSIONED_OBJECT, which identifies source EHR.

1..1

time_created: DV_DATE_TIME

Creation time of original VERSIONED_OBJECT.

1..1

total_version_count: Integer

Total number of versions in original VERSIONED_OBJECT at time of creation of this X_VERSIONED_OBJECT.

1..1

extract_version_count: Integer

The number of Versions in this extract for this Versioned object, i.e. the count of items in the versions attribute. May be 0 if only revision history is requested.

0..1

revision_history: REVISION_HISTORY

Optional revision history of the original VERSIONED_OBJECT. If included, it is the complete revision history.

0..1

versions: List<ORIGINAL_VERSION>

0 or more Versions from the original VERSIONED_OBJECT, according to the Extract specification.

5.3.3. X_VERSIONED_EHR_ACCESS Class

Class

X_VERSIONED_EHR_ACCESS

Description

Form of X_VERSIONED_OBJECT for EHR_ACCESS EHR object.

Inherit

X_VERSIONED_OBJECT

5.3.4. X_VERSIONED_EHR_STATUS Class

Class

X_VERSIONED_EHR_STATUS

Description

Form of X_VERSIONED_OBJECT for EHR_STATUS EHR object.

Inherit

X_VERSIONED_OBJECT

5.3.5. X_VERSIONED_COMPOSITION Class

Class

X_VERSIONED_COMPOSITION

Description

Form of X_VERSIONED_OBJECT for COMPOSITION EHR object.

Inherit

X_VERSIONED_OBJECT

5.3.6. X_VERSIONED_FOLDER Class

Class

X_VERSIONED_FOLDER

Description

Form of X_VERSIONED_OBJECT for FOLDER EHR object.

Inherit

X_VERSIONED_OBJECT

5.3.7. X_VERSIONED_PARTY Class

Class

X_VERSIONED_PARTY

Description

Form of X_VERSIONED_OBJECT for PARTY demographic object.

Inherit

X_VERSIONED_OBJECT

6. Generic_extract Package

6.1. Overview

The rm.extract.generic_extract package defines a kind of Extract designed to be used by non-openEHR systems (including EHR/EMR systems) that want to send data to another system using openEHR structures defined by archetypes and templates. Such systems typically do not natively contain standardised data of any kind, and usually have quite variable and idiosyncratic support for versioning. The following UML diagram illustrates the rm.extract.generic_extract package.

RM ehr extract.generic extract
Figure 11. rm.extract.generic_extract Package

The figure below illustrates the instance structure of a typical GENERIC_EXTRACT. The containment structure is shown in blue, and content item wrappers (meta-data) in yellow.

typical generic extract
Figure 12. Typical generic extract structure

6.2. Design

6.2.1. Structure

The GENERIC_CONTENT_ITEM subtype of EXTRACT_CONTENT_ITEM defines meta-data more or less of which can be populated by typical legacy systems, as well as document sources such as IHE/XDS repositories. Various groups of meta-data are defined: document type / status information, commit audit details and document lifecycle information.

The document meta-data items are as follows:

  • item_type: a coded term indicating the content 'model' or schema, which may be a published standard, and/or some kind of archetype, template or similar content control artefact;

  • item_type_version: version of the item_type model.

The next group of items defines details of creation of the original information. In some systems, this is the same as 'committal', i.e. the act of creating and committing the original data to the system. In other cases, the information in the extract is being assembled for the first time for the purposes of the extract, and the audit information therefore corresponds to this act. The audit details are as follows:

  • author: identity of the author of the original content - this is a UID reference to a demographic item in another part of the current extract;

  • creation_time: date/time when the content was created;

  • authoriser: identity of a professional who authorised this content, if relevant - this is a UID reference to a demographic item in another part of the current extract;

  • authorisation_time: date/time when the content was authorised;

  • item_status: lifecycle status of the content;

  • version_id: version of this particular instance of the content item when it was created and/or committed, in environments where versioning is supported;

  • version_set_id: 'version set' identifier, i.e. identifier of group of versions which together constitute a set of versions in time of a given logical content item;

  • system_id: system where the content was created / committed to / extracted from;

  • other_details: other meta-data, in the form of a keyed list of Strings.

All of these items are optional, reflecting their varying availability in different source systems. An archetype or template of the Extract may force some or all to be mandatory for specific kinds of Extract.

The item attribute carries content which may be any openEHR LOCATABLE structure, including things like COMPOSITION, any kind of ENTRY including GENERIC_ENTRY, ITEM_TREE, or even CLUSTER. This is assumed to have been converted by some data transformation process from data within the original system.

6.2.1.1. Demographic Referencing

Within the content a generic Extract, expressed using openEHR COMPOSITIONs, participations are expressed using intances of PARTICIPATION. This is clearly somewhat inefficient for the required use here, since they will be constructed on the fly from simpler non-openEHR data, and a more flexible variant may be required for the future.

To Be Determined: a more efficient participation reference mechanism, to support participations constructed on the fly for the purposes of the Extract.

6.3. Class Descriptions

6.3.1. GENERIC_CONTENT_ITEM Class

Class

GENERIC_CONTENT_ITEM

Description

Single item in generic extract, designed for 13606 and CDA data.

Inherit

EXTRACT_CONTENT_ITEM

Attributes

Signature

Meaning

0..1

item_type: DV_CODED_TEXT

Identifier of model or schema used to create the content.

0..1

item_type_version: String

Version of model or schema used to create the content item.

0..1

author: String

Reference to a demographic entity elsewhere in this Extract representing the author of the item version. The reference should be a UID corresponding to the UID of a GENERIC_CONTENT_ITEM containing the demographic information.

0..1

creation_time: Iso8601_date_time

Time of creation of this item version on the original system. This may be an earlier commit time, or it may be the time at which the item was created during the Extract generation process.

0..1

authoriser: String

Reference to a demographic entity elsewhere in this Extract representing an authoriser of the item version, if relevant. The reference should be a UID corresponding to the UID of a GENERIC_CONTENT_ITEM containing the demographic information.

0..1

authorisation_time: Iso8601_date_time

Time of authorisation of this item version on the original system where relevant.

0..1

item_status: DV_CODED_TEXT

Coded lifecycle status of the item.

0..1

version_id: String

Version id of this item in original system.

0..1

version_set_id: String

Version set id of this item in original system, where applicable.

0..1

system_id: String

Identifier of EMR or other system from which the item was created / extracted. Typically in the form of a domain name.

0..1

other_details: Hash<String, String>

Other details about the content item.

0..1
(redefined)

item: LOCATABLE

Content object.

7. Synchronisation Extracts

7.1. Overview

The UML diagram below illustrates an Extract variant designed for synchronising two openEHR systems. The specification only allows for a list of Contributions, or Contributions since a certain Contribution; it also allows the actual versions to be included or excluded. If they are excluded, you can get just Contributions on their own - i..e find out what the other system has got.

RM ehr extract.sync extract
Figure 13. rm.extract.synchronisation_extract Package

7.2. Class Descriptions

7.2.1. SYNC_EXTRACT_REQUEST Class

Class

SYNC_EXTRACT_REQUEST

Description

Type of request designed for synchronisation of Contributions between openEHR servers.

Inherit

MESSAGE_CONTENT

Attributes

Signature

Meaning

1..1

specification: SYNC_EXTRACT_SPEC

Details of specification of synchronisation request.

7.2.2. SYNC_EXTRACT Class

Class

SYNC_EXTRACT

Description

Inherit

MESSAGE_CONTENT

Attributes

Signature

Meaning

1..1

specification: SYNC_EXTRACT_SPEC

Details of specification of this Extract.

0..1

items: List<X_CONTRIBUTION>

Content, in the form of a serialised Contributions.

7.2.3. SYNC_EXTRACT_SPEC Class

Class

SYNC_EXTRACT_SPEC

Description

Details of specification of Extract, used in a request to specify an Extract, or in a response, to describe what is actually in the Extract.

Attributes

Signature

Meaning

1..1

includes_versions: Boolean

True if the Versions from the Contribution are included; False if just the Contribution and its Audit are included.

0..1

contribution_list: List<HIER_OBJECT_ID>

List of Contributions to include / that are included in the Extract.

0..1

contributions_since: DV_DATE_TIME

Specify Contributions included in Extract by threshold date.

0..1

all_contributions: Boolean

True if all Contributions in the record are included.

7.2.4. X_CONTRIBUTION Class

Class

X_CONTRIBUTION

Description

Serialised form of Contribution for an Extract.

Attributes

Signature

Meaning

1..1

uid: HIER_OBJECT_ID

Uid of Contribution in source system.

1..1

audit: AUDIT_DETAILS

Audit of Contribution in source system.

0..1

versions: List<VERSION>

Serialised Versions from Contribution in source system.

8. The Message package

8.1. Requirements

In the first two EHR extract scenarios described in Requirements on page 8, extracts may be received in response to a request, or they may be unsolicited. Most transfers of care (e.g. discharge summaries and referrals) and pathology test results will generate unsolicited extracts, whereas solicited requests will usually occur due to the patient presenting him or herself in another part of the health system without an explicit transfer of care.

8.2. Design

The message package provides the basic abstractions for the sending and receiving of any point to point message containing a payload, of abstract type MESSAGE. The message Package is illustrated in the UML diagram below.

RM ehr extract.message
Figure 14. rm.message Package

A new message is required for each transmission, even if the payload was created once and is retransmitted multiple times.

8.2.1. Integrity and Security

The MESSAGE object may include a digital hash (i.e. digest or digital finderprint) of the serialised content, made for example using the SHA-1 or MD5 algorithms. The purpose of the digest is to provide an integrity check on the data. This protects against non-malicious changes to the data (e.g. due to software bugs, incorrect transaction management). Often this will be acceptable within secure, closed environments, such as a private hospital or community health network.

Protection against malicious modification can be provided by encryption.

To Be Determined: normalised serialised expression

8.3. Class Descriptions

8.3.1. ADDRESSED_MESSAGE Class

Class

ADDRESSED_MESSAGE

Description

The concept of a message addressed to nominated recipients.

Attributes

Signature

Meaning

1..1

sender: String

Party sending the message.

1..1

sender_reference: String

Identification of message used by sender. This will be the same no matter how many times this message is sent to these recipients.

1..1

addressees: List<String>

Intended recipients, in the form of internet addresses.

0..1

urgency: Integer

Urgency with which destination should deal with message:

  • -1 - low

  • 0 - normal

  • 1 - high

1..1

message: MESSAGE

The content of the message.

8.3.2. MESSAGE Class

Class

MESSAGE

Description

A “message” is an authored, possibly signed, piece of content intended for one or more recipients. Since the recipient may or may not be known directly, recipients are specified in the ADDRESSED_MESSAGE class.

Constants

Signature

Meaning

1..1

author: PARTY_PROXY

Party responsible for the message content, who may or may not be technically responsible for its creation (e.g. by data entry etc).

Attributes

Signature

Meaning

1..1

audit: AUDIT_DETAILS

Details of who actually created the message and when. This is the person who entered the data or otherwise caused the message to be created, or might be a piece of software.

1..1

content: MESSAGE_CONTENT

Content of the message.

0..1

signature: String

Optional signature by the author of message content in openPGP format. The signature is created as a Hash and optional signing of the serialisation of this message object with this signature field Void.

9. Semantics of openEHR and ISO 13606 extracts

9.1. Versioning Semantics

Although for most clinical situations, it is the latest versions of Compositions which are sent to a receiver, there are requirements for various amounts of version-related information to be included, as described in Requirements on page 8. At a minimum, Compositions always include the audit trail corresponding to the particular version which the Composition represents. In some cases, historical versions of a logical Composition are needed for some medico-legal reason. It may even be required that the receiver system wants to reconstruct a complete facsimile of the versioned object, logically identical to its form at the source (but most likely stored in a different versioning implementation). The openEHR extract specification defines the simplest means of satisfying these needs, namely to include all Compositions in their whole form, including in the case where they are successive versions of a single logical Composition such as "family history", as illustrated in the figure below. The main justification for this is that no assumptions should made on sender or receiver systems to do with their ability to represent or efficiently process versions. Whole Compositions can always be processed by even the simplest systems.

composition versioning
Figure 15. Successive Composition versions in a logical Transaction

It is assumed that any system that wants to be able to determine things such as who was responsible for changing a certain fragment of a Composition, when some part of a Composition came into being, or the differences between two particular versions of a Composition, must have version control capability locally. This usually means having some implementation of a version control model such as the one described in the openEHR Common Reference Model, which can do efficient versioning, differencing and so on. Supplying Compositions in their full form ensures that no assumption is made on what such an implementation might be.

This approach is a departure from the ISO 13606-1:2008 EHR Extract standard, which defines Compositions so as to include revision history information on every node of the structure. Although it is not stated in the 13606 specification whether the 'Composition' is in fact supposed to be understood as a copy of a Composition from an EHR, or as a 'cumulative diff' of Composition versions in an EHR, analysis shows that only the latter can make sense because the Composition (Composition) is the unit of creation and modification, and there is logically only one audit trail for each version. Even the 100th version has associated with it only one audit trail.

This raises the question of whether a 'diff' form of Compositions should be used in the openEHR Extract, conforming to the ISO standard. The approach was not chosen for a number of reasons:

  • it implies that senders can generate 'diff' information structures and that receivers can process them, i.e. it makes more assumptions than necessary about the sophistication of systems;

  • the ISO specification appears to be in error with respect to deletions - the sending of logical deletions does not appear to be handled properly;

  • the sending of deletions is not normally desired, and may be illegal (e.g. in Europe there are EC directives preventing the sending of statements corrected by clinicians or patients).

It is worth contemplating just how complex cumulative difference information would be. The following figure illustrates the structure generated by the accumulation of only three changes shown in the successive versions in the figure below. The large numbers of changes likely in persistent Compositions will generate far more complex structures.

cumulative diff
Figure 16. Generation of Cumulative Difference Form

In conclusion, while sending a difference form of Compositions is not out of the question in a future when EHR systems are routinely capable of sophisticated version handling, it is considered too complex currently, and the controls over sending deleted information have not been sufficiently well described.

9.2. Creation Semantics

The following describes an algorithm which guarantees the correct contents of an EHR extract. The input to the algorithm is:

  • the list of EHR Compositions required in the extract (the "primary" Composition set);

  • optionally a folder structure in which the Compositions are to be structured in the extract;

  • the include_multimedia flag indicating whether DV_MULTIMEDIA content is to be included inline or not;

  • the follow_links attribute indicating to what depth DV_LINK references emanating from Compositions should be followed and the Compositions containing the link targets also included in the extract.

The algorithm is as follows.

  • Create a new EHR_EXTRACT including the folder structure;

  • Create a demographics EXTRACT_CHAPTER and write the PARTYs in;

  • For each Composition in the original set, do:

    • create an X_VERSIONED_COMPOSITION, and set is_primary;

    • for each instance of OBJECT_REF encountered (e.g. PARTY_REF), obtain the target of the reference from the relevant service, and copy it to the appropriate chapter, e.g. demographics, access_groups tables with the key = the OBJECT_REF.id;

    • copy/serialise the Composition into the appropriate place in the folder structure rewriting its OBJECT_REFs so that namespace = "local"

    • for each instance of DV_MULTIMEDIA encountered, include or exclude the content referred to by the uri or data attributes, according to the include_multimedia flag;

    • according to the value of follow_links, for each instance of DV_LINK encountered (only from/to Archetyped entities):

  • follow the links recursively. For each link: create an X_VERSIONED_COMPOSITION; set is_primary = False, write the path and write the target Compositions in the extract if not already there;

  • create the DV_LINK objects so that their paths refer correctly to the Compositions in the Extract;

TBD: do something about Access_control objects;

References

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Resources

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e-Health Standards

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e-Health Projects

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General Standards

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  2. [IEEE_828] IEEE. IEEE 828-2005: standard for Software Configuration Management Plans.

  3. [ISO_8601] ISO 8601 standard describing formats for representing times, dates, and durations. See https://en.wikipedia.org/wiki/ISO_8601.

  4. [ISO_2788] ISO. ISO 2788 Guide to Establishment and development of monolingual thesauri.

  5. [ISO_5964] ISO. ISO 5964 Guide to Establishment and development of multilingual thesauri.

  6. [Perl_regex] Perl.org. Perl Regular Expressions. Available at http://perldoc.perl.org/perlre.html .

  7. [rfc_2396] Berners-Lee T. Universal Resource Identifiers in WWW. Available at http://www.ietf.org/rfc/rfc2396.txt. This is a World-Wide Web RFC for global identification of resources. In current use on the web, e.g. by Mosaic, Netscape and similar tools. See http://www.w3.org/Addressing for a starting point on URIs.

  8. [rfc_2440] RFC 2440: OpenPGP Message Format. See http://www.ietf.org/rfc/rfc2440.txt and http://www.ietf.org/internet-drafts/draft-ietf-openpgp-rfc2440bis-18.txt

  9. [rfc_3986] RFC 3986: Uniform Resource Identifier (URI): Generic Syntax. IETF. See http://www.ietf.org/rfc/rfc3986.txt .

  10. [rfc_4122] RFC 4122: A Universally Unique IDentifier (UUID) URN Namespace. IETF. See http://www.ietf.org/rfc/rfc4122.txt .

  11. [rfc_2781] IETF. RFC 2781: UTF-16, an encoding of ISO 10646 See http://tools.ietf.org/html/rfc2781.

  12. [rfc_5646] IETF. RFC 5646. Available at http://tools.ietf.org/html/rfc5646.

  13. [sem_ver] Semantic Versioning. http://semver.org .

  14. [Xpath] W3C Xpath 1.0 specification. 1999. Available at http://www.w3.org/TR/xpath.

  15. [uri_syntax] Uniform Resource Identifier (URI): Generic Syntax, Internet proposed standard. January 2005. see http://www.ietf.org/rfc/rfc3986.txt .

  16. [w3c_owl] W3C. OWL - the Web Ontology Language. See http://www.w3.org/TR/2003/CR-owl-ref-20030818/ .

  17. [w3c_xpath] W3C. XML Path Language. See http://w3c.org/TR/xpath .