A versioned layer from one catalog can be used in another to produce a catalog that combines existing data with other data. When data is shared between catalogs, the dependencies between catalogs are listed in the catalog configuration as version dependencies. A version dependency indicates the catalog HRN, dependency type (direct or indirect), and version number that the catalog depends on to produce a consistent set of data across layers. For example, if you have a catalog that depends on version 12 of Catalog A, then catalog A is updated to version 13, that update may change the data in a way that produces an inconsistency with the data in your catalog. So, your catalog's configuration includes a Catalog A version 12 as a version dependency so that newer versions of Catalog A are not used in your catalog. If you were to update the data in your catalog to be compatible with Catalog A version 13, you would update your catalog's version dependency to Catalog A version 13.
A catalog's depdendencies refer not only to the catalogs that a catalog depends on directly, but also those depended on by the dependenices, through the entire linage of dependnecies. For example, consider this scenario:
In this case, the dependencies for Catalog A would be:
In this case, Catalog B version 13 is a direct depenency and Catalog C version 9 is an indirect dependency. The type of dependency (direct or indirect) is indicated by a flag in the version dependency information.