Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
The provides detailed background and further information on ECL. Its Appendices contain many examples of expressions, covering both valid and invalid expressions, direct aliases and Reference Set fields, as well as an ECL Quick Reference:
The Public MRCM Maintenance Tool presents a human-readable and navigable interface for the rules and constraints applicable to the SNOMED CT concept model.
It provides an online interactive MRCM reference for SNOMED CT content authors and reviewers.
Anyone with a Chrome web browser, so long as it is for reference and educational purposes.
Any time, subject to occasional maintenance - the service is an online web-based application running continuously between occasional scheduled or emergency maintenance.
Scheduled maintenance may include new features, improvements, defect fixes and hosting environment updates.
Emergency maintenance may include operating system patches and security updates as well as high priority defect fixes.
Operating System and hardware specifications as for Chrome.
Minimum monitor resolutions:
1600 x 900 px (HD+ 16:9)
1680 x 1050 px (WSXGA+ 16:10)
1600 x 1200 px (UXGA 4:3)
Internet connection:
Broadband (4G minimum)
Other combinations of web browsers, machine hardware, lower screen resolutions and slower internet connectivity may still work but are not optimized and not supported.
The Domain panel shows a nested tree-view listing of SNOMED CT domains.
Scroll up and down the listing via the scroll-bar to the right of the Domain panel, move up and down the list via your keyboard and keys, or drag your cursor onto the desired Domain name until it is highlighted.
The domain names are active - pressing one will change the context of the Applicable Attributes panel to those matching the domain, and also expand the Domain Details sub-panel at the base of the Domain panel.
The Domain Details sub-panel can be toggled closed/open when a domain name is selected.
This presents details corresponding to the MRCM domain reference set fields for the selected domain:
Domain Constraint (ECL expression)
Proximal Primitive Constraint (ECL expression)
The Expression Constraint Language is a formal syntax for representing SNOMED CT expression constraints.
Expression constraints are computable rules used to define a bounded sets of clinical meanings represented by either precoordinated or postcoordinated expressions.
Expression constraints can be used to restrict the valid values for a data element in an EHR, as the intensional definition of a concept-based reference set, as a machine processable query that identifies a set of matching expressions, or as a constraint that restricts the range of an attribute defined in the SNOMED CT concept model.
The has full details on ECL, including use cases, requirements, logical model, syntax specification, examples, and implementation considerations.
Precoordination Domain Template (ECL expression)
Postcoordination Domain Template (ECL expression)
When open, press on the right of the sub-panel title bar to close the Domain Details sub-panel.
When closed, press in the sub-panel title bar to open it.
The listed domains can be filtered by typing match text into the Filter Domains... text box above the list.
Matching begins as soon as the first character is entered, and progressively filters as further characters are entered.
Domains can also be filtered by entering an SCTID into the Filter Domains... text box.
If the SCTID matches an MRCM domain then only that domain is presented (since its SCTID is an exact match).
If an entered SCTID does not match an MRCM domain then the domain list will be blank.
Clear the Filter Domains... box by deleting the text, or move the cursor to the far right of the text entry box to reveal an X button, then press the X button to clear the entire text and re-show all domains.
Alternatively, press RESET to the right of the context and actions bar (upper right corner above the three main content panels).
Since this action button also clears other selections such as Attributes and Attribute Ranges, a pop-up panel is presented to confirm the request.
Press RESET in the confirmation panel to clear all three content panels back to their initial view state, or press CANCEL to return to the current view without clearing.
EITHER Press MRCM Browser in the SCT Browser landing page.
OR Enter the MRCM Maintenance Tool address directly in your web browser (for example from a bookmark).
The MRCM Maintenance Tool opens in a new tab/window (depending on your web browser options), containing:
Branding and identity header
Context and actions bar
Domain panel
Applicable Attributes panel
Attribute Range panel
Copyright notice, help and contact us footer
The header contains site branding and an MRCM version selector to its left (the default selection is the last published SNOMED CT release).
Below the header, the context and actions bar runs across the three main content panels.
Currently selected items appear to the left of this bar (initially empty when nothing is selected), and a RESET button is available to its right (this clears any selections and initializes the content panels).
The Domain panel shows a nested tree-view listing of SNOMED CT domains.
Navigate the tree-view listing to browse the domains.
By default the Applicable Attributes panel shows all available attributes.
When an applicable attribute is selected, the Attribute Range panel shows that attribute's range details.
The footer contains a copyright notice, help link (which opens this guide), and a contact us link (identical to that in the Authoring Platform footer).
Browse older versions of the MRCM
Use the header Version drop-down selector to set the version of MRCM to be browsed.
The other options are previous published versions of SNOMED CT, each of which shows the MRCM details for that version.
Find the desired domain name in the Domain panel of the MRCM Maintenance Tool.
Press the name to change the context of the Applicable Attributes panel to those matching the domain, and also expand the Domain Details sub-panel at the base of the Domain panel.
The selected domain name is highlighted.
The Domain Details sub-panel can be toggled closed/open when a domain name is selected.
This presents details corresponding to the MRCM domain reference set fields for the selected domain:
The Applicable Attributes list can be filtered by typing a text pattern into the Filter Attributes... box.
As soon as text is entered, the attributes list will update to only show those matching the filter text (which may only be one, or none at all).
With no Domain or Applicable Attribute selected, browse the Applicable Attributes list to locate the attribute you need.
Press the attribute to select it.
The domain(s) to which it applies are highlighted in the Domain panel.
Selecting the attribute also shows its Attribute Details and populates the Attribute Range panel.
The attribute FSN term (or part of) can be applied as a text filter to the Applicable Attributes list, to narrow down the options and save scrolling the full list.
This is particularly useful if the attribute term starts with a letter lower down the list which is alphabetically sorted.
Parent Domain (sub-domains only)
Proximal Primitive Constraint (ECL expression)
Guide URL (link to the relevant section of the SNOMED CT Editorial Guide)
Precoordination Domain Template (ECL expression)
Postcoordination Domain Template (ECL expression)
When open, press on the right of the sub-panel title bar to close the Domain Details sub-panel.
When closed, press in the sub-panel title bar to open it.
The Applicable Attributes list can also be filtered by entering an SCTID into the Filter Attributes... box.
If the SCTID matches an attribute applicable to the selected domain then only that attribute is presented (since its SCTID is an exact match).
If an entered SCTID does not match an attribute applicable to the selected MRCM domain then the attribute list will be blank.
If a sub-domain is selected, the Applicable Attributes results will show all those applicable to its parent domain, however only those applicable to the selected sub-domain will be active in the list.
Any attributes not applicable to the selected sub-domain will be inactive, and moving the cursor onto them will show a symbol, indicating they cannot be viewed for the selected sub-domain.
Find the desired applicable attribute name in the Applicable Attributes panel listing.
Press the name to change the context of the Attribute Range panel to those matching the attribute, and also show the Attribute Details sub-panel at the base of the Applicable Attributes panel.
The selected attribute name is highlighted.
The Attribute Details sub-panel shows values for:
Grouped (checkbox)
Attribute Cardinality (range)
Attribute in Group Cardinality (range)
Rule Strength (text)
Content Type (text)
The Attribute Range panel shows the following details for the selected attribute:
Range Constraint (ECL expression)
Attribute Rule (ECL expression)
Rule Strength (text)
On selecting an applicable attribute, a search is performed to retrieve all concepts matching the range constraints.
After a brief pause (search time depends on the complexity of the search and number of results obtained) the results are presented in a sub-panel at the base of the Attribute Range panel.
The Attribute Details sub-panel can be toggled closed/open when an attribute is selected.
When open, press on the right of the sub-panel title bar to close the Attribute Details sub-panel.
When closed, press in the sub-panel title bar to open it.
If the SCTID is known, entering it into the Filter Attributes... box will immediately filter the Applicable Attributes list to show only that attribute.
The following fields can be expanded to show a formatted human-readable presentation of their ECL expression:
Domain Details - Precoordination Domain Template
Domain Details - Postcoordination Domain Template
Attribute Range - Range Constraint
This example shows the Domain Details - Postcoordination Domain Template ECL expression for the | Anatomical structure (body structure) | MRCM sub-domain.
Attribute Range - Attribute Rule
To show the ECL Expression overlay press in the right corner of the field entry.
A pop-up overlay is presented which contains a formatted version of the field value ECL expression.
The example to the right shows the Domain Details - Precoordination Domain Template ECL expression for the | Anatomical structure (body structure) | MRCM sub-domain.
Press X in the top right corner of the overlay, or press CLOSE in the lower right corner of the overlay to return to the underlying MRCM Maintenance Tool view.
This example shows the Attribute Range - Range Constraint ECL expression for the | Laterality (attribute) | MRCM attribute.
This example shows the Attribute Range - Attribute Rule ECL expression for the | Laterality (attribute) | MRCM attribute.
This is a guide to using the Public SNOMED MRCM Maintenance Tool (MRCMMT) - a website service which supports browsing and querying of SNOMED CT MRCM (Machine Readable Concept Model) domain-specific authoring rules and related attributes constraints.
With the Public MRCMMT you can:
Browse the MRCM rules for SNOMED CT constrained domains, associated attributes and their applicable ranges.
See ECL expression constraints for domains and attributes.
See the domains associated with a particular attribute.
See the attributes associated with MRCM-constrained sub-domains.
See which concepts match a selected domain, attribute and attribute range.
The Public MRCMMT is in use here:
© Copyright 2026 International Health Terminology Standards Development Organisation, all rights reserved.
This document is a publication of International Health Terminology Standards Development Organisation, trading as SNOMED International. SNOMED International owns and maintains SNOMED CT®.
Any modification of this document (including without limitation the removal or modification of this notice) is prohibited without the express written permission of SNOMED International. This document may be subject to updates. Always use the latest version of this document published by SNOMED International. This can be viewed online and downloaded by following the links on the front page or cover of this document.
SNOMED®, SNOMED CT® and IHTSDO® are registered trademarks of International Health Terminology Standards Development Organisation. SNOMED CT® licensing information is available at . For more information about SNOMED International and SNOMED International Membership, please refer to or contact us at .
The Machine Readable Concept Model (MRCM) represents rules in the SNOMED CT concept model in a form that can be read by a computer and applied to test that concept definitions and expressions comply with the rules. The MRCM may be used for a variety of purposes, including the authoring and validation of SNOMED CT concepts, expressions, expression constraints and queries, Natural Language Processing and terminology binding to support semantic interoperability.
The MRCM may be useful in a number of use cases, including:
Development of precoordinated terminology content.
Authoring and validation of SNOMED CT expressions, constraints and queries.
Natural Language Processing.
Terminology binding to information models, for purposes such as data capture and semantic interoperability.
The MRCM contains a set of domains and a set of attributes, which may be applied to one or more domains.
The cardinality and valid range of each attribute is specified, and indicates whether or not the attribute should be grouped.
The domain, range, cardinality and grouped indicator for each attribute is also combined into a single 'attribute rule', which is represented using a .
For each domain, the set of valid attributes and their associated rules are compiled into two SNOMED CT 'domain templates' – for precoordinated concept authoring and postcoordinated expression authoring respectively.
These domain templates may be further specialized to support customized authoring of specific subdomains.
The following diagram summarizes the logical structure of the MRCM:
The MRCM is distributed as the following types of reference set in the SNOMED CT RF2 release file format:
MRCM Domain Reference Set
MRCM Attribute Domain Reference Set
MRCM Attribute Range Reference Set
MRCM Module Scope Reference Set
The following diagram summarizes these reference sets and their properties:
