Purpose

The 900000000000534007 | Module dependency reference set| represents dependencies between different SNOMED CT release modules. In each case, the dependency indicates which targetEffectiveTime (field) of each particular module a given sourceEffectiveTime (field) of the dependent module requires.

Data structure

The Module dependency reference set is a String (data type) - String (data type) reference set which is used to represent dependencies between modules, taking account of module versioning. Its structure is shown in the following table.

Notes on usage

Module version dependencies are represented using a single 900000000000534007 | Module dependency reference set| . Thus all module dependency rows have the same refsetId ( 900000000000534007 | Module dependency reference set (foundation metadata concept)| ).

It is the responsibility of the organization owning and maintaining a dependent module to identify all modules on which it depends. They do this by adding rows to the 900000000000534007 | Module dependency reference set| within the dependent module. Because these added member must be in the dependent module, the moduleId (field) of the reference set member record is also the identifier of the dependent (source) module. The target module on which the source module depends is identified by the referencedComponentId (field) .

A module version may depend on one or more other module versions, and many module versions may have a dependency on a single module version. Cyclic module version dependencies are not allowed. If module-A depends on module-B, then module-B cannot depend on module-A.

Dependencies are not transitive and this means that dependencies cannot be inferred from a chain of dependencies. If module-A depends on module-B and module-B depends on module-C, the dependency of module-A on module-C must still be stated explicitly.

Any release should consist of a set of module versions that are certified as being compatible. Each release should also identify other module versions that it is dependent on even when these are outside the scope of the release. For example, the dependencies of modules in an Extension on the International Release must be stated.

Dependencies are specified between module versions, not just dependencies between modules. Therefore, it is possible to specify a dependency from a module released on one date to an earlier version of another module. The version of the dependent module is specified by the sourceEffectiveTime (field) and the version of the module on which it depends is specified by the targetEffectiveTime (field).

Note: Current practice assumes the refset.id column contains the same identifier for all versions of the dependencies between the same pair of modules. This approach means that at any given time only one version of each module has effective dependencies. Therefore, to review the dependencies of an earlier version, a snapshot for an earlier time must be checked. An alternative approach has been suggested by some people in which a new identifier is allocated to each dependency of each module. This would then mean that all past dependencies would be visible in a snapshot view. It would also mean that it would be possible release updated dependencies for an existing module version while also releasing more up-to-date versions of the same module with different dependencies. This added flexibility comes at the price of additional complexity and for the time-being the International Release continues to use the simpler approach in which each new version of a dependency supersedes the dependency between earlier versions of the same pair of modules.

Metadata

The following metadata in the "Foundation metadata concept " hierarchy supports this reference set :

• 900000000000454005 | Foundation metadata concept|
  • 900000000000455006 | Reference set|
    • 900000000000534007 | Module dependency|

Each component within a SNOMED CT release references a moduleId (field). This is the module that the component is currently mastered in (from the effectiveTime (field) held on the component record). A module is simply a collection of SNOMED CT components that are maintained as a unit by a single organization. It is the organization 's responsibility to organize the components in each extension that it is responsible for into one or more modules, in a way that best fits its business needs.

A module is modeled by a descendant of 900000000000443000 | Module| in the metadata hierarchy. The 900000000000443000 | Module| sub - hierarchy is organized by a maintaining organization into a number of groups. For example, all modules maintained by SNOMED International will be children of 900000000000445007 | SNOMED International maintained module| . The 900000000000443000 | Module| sub-hierarchy models modules maintained by each organization and does NOT model module dependencies. Instead, module dependencies are modeled using the 900000000000534007 | Module dependency reference set| .

At the point of release, if any component within a module has changed, then a new row will be added to 900000000000534007 | Module dependency reference set| for the module's concept, with the effectiveTime (field) set to the date of the new release, irrespective of whether the other fields in the module concept record itself have changed. The updated |Module| concept record identifies that some components within the module have been updated in this release. Where no components within a module have been updated, then a new module record will not be added and the module's effectiveTime (field) field will not change from the previous release.

Each component will be in one, and only one component. The module that a component is mastered in may change over time, and when this happens, the component's moduleId (field) field will be updated (in the usual way by appending a row for the component).

Each module will be in one and only one extension. Modules will not straddle extensions. The extension that a module resides in is defined by the SCTID (data type) of the module. A module may not move from one extension to another over time. If the components within a module are to be moved to another extension, then a new module must be created within the destination extension to host the components that are to be transferred.

There may be more than one module in an extension .

Descriptor

The table below shows the descriptor that defines the structure of the 900000000000534007 | Module dependency reference set| .

Note: The table above omits the initial four columns of data present in the release file. These follow the standards versioning pattern id (field), effectiveTime (field), active (field), active (field). Additionally, to aid understanding, the table above also shows the term from one of the descriptions associated with each of the identified concept. The release file only contains the identifier .

Module dependency reference set example

The table below holds example entries for the 900000000000534007 | Module dependency reference set| in a snapshot view of the January 2014 SNOMED CT International Release .

This SNOMED CT International Release contains three modules:

• 900000000000012004 | SNOMED CT model component| which has no dependencies;
• 900000000000207008 | SNOMED CT core| which depends on the 900000000000012004 | SNOMED CT model component| ; and
• 449080006 | SNOMED CT to ICD-10 rule-based mapping module| which depends on both the other modules.

In this case all the 2014-01-31 modules depend on 2014-01-31 versions of the other modules. However, in some case a module may depend on an earlier version of another model (e.g. an extension module may be releases after the SNOMED CT International Release to which it applies).

Dependencies are not transitive. The fact that 449080006 | SNOMED CT to ICD-10 rule-based mapping module| is dependent on 900000000000207008 | SNOMED CT core| may seem to imply a dependency on 900000000000012004 | SNOMED CT model component| . However, in practice all dependencies must be explicitly specified, not just immediate dependencies.

Note: The tables above omit the initial three columns of data present in the release file. These follow the standards versioning pattern id (field), effectiveTime (field), active (field). Additionally, to aid understanding, the tables above also show the term from one of the descriptions associated with each of the identified concept. The release file only contains the identifier .