The BDC Model Concept
Last modified: April 15, 2010
Applies to: SharePoint Server 2010
Entities (external content types) are globally addressable and they can form a unit of deployment. However, this requires all Entities to exist in their own LobSystem object. You must duplicate information when several Entities are sourced from the same system. To avoid this, Microsoft Business Connectivity Services (BCS) maintains the concept of multiple Entities in one LobSystem, but extends the metadata package XML file format and makes it possible to define multiple LobSystems in a single file. Thus, the LobSystem is no longer the root tag in the XML and is replaced by a new tag named Model.
Within the Business Data Connectivity (BDC) service, a Model is represented as a collection of references to Entities, or as an m:n relationship between Entities. A Model is a unit of portability for Entities and LobSystems; in this role it is comparable to a Visual Studio project. Administrators can import and export a model (parameterized via the PackageContents enumeration) as they could with LobSystems in Office SharePoint Server 2007. However, because Entities are have namespaces, two Models may define the same LobSystems and Entities so that, when a Model is deleted, the delete operation cascades to all referenced Entities that are not referenced by any other Models. In addition, it cascades the delete operation to all LobSystems referenced by those Entities, if they are not referenced by any Entities that are unaffected by the delete cascade.
Models names are required to be unique in a Business Connectivity Services service application. Models are not versioned.