Each CA IDMS central version must have one, and only one, system dictionary. A dictionary is designated as a system dictionary by assigning it a name of SYSTEM in the database name table used by the central version. A central version accesses its system dictionary to retrieve configuration information, such as the DC/UCF system definitions, database definitions, and security information that control the execution of the central version.
While it is possible to use a system dictionary as a repository for application definitions, we recommend that this not be done. Define one or more application dictionaries for this purpose instead. Clearly separating the use of the two ensures that the central version is not affected if application information must be recovered. It also makes it easier to control changes to configuration settings.
The following diagram illustrates the separation of system and application dictionaries on central version IDMS21.
We also recommend that each central version have its own system dictionary. Doing this eliminates the interdependence between central versions and makes it possible to restore one central version's configuration without affecting that of another. In most cases this is the best way to set up your environment; however, sometimes it is useful for multiple central versions to share a single system dictionary. This is the case when central versions are intended to always have the same runtime attributes. In this situation maintaining the configurations is easier if they all reside in one system dictionary.
The following diagram illustrates both segregating and sharing system dictionaries and configuration information. Central versions IDMS21 and IDMS46 each have their own system dictionary and configuration information because their runtime attributes are not similar. Central versions IDMS50 and IDMS51 share a system dictionary and configuration information because their runtime attributes are meant to be identical.