Represents a relationship between two or more related external content types within external systems.
Assembly: Microsoft.BusinessData (in Microsoft.BusinessData.dll)
An association can have one or more sources and a single destination. For example, to obtain a list of Sales Orders, you may need to supply a Customer and a Sales Area. In this example, "Sales Orders" is the retrieved object, thus the destination. "Customer" and "Sales Area" are input objects, thus sources.
Foreign Key vs. Non-Foreign Key
Business Data Connectivity (BDC) service categorizes the associations with respect to how the association information is represented. You should be aware of this distinction, as each category requires different approaches when working with associations. Associations that are based on foreign keys store the relationship of external items within the data of one of these external items. Associations that are not based on foreign keys store the relationship information in a store external to both of these items. For example, consider a Customer item and an Order item. If the Order item contains an attribute which identifies the related Customer item, then this association is foreign-key based.
BDC distinguishes between these categories by the presence of a foreign identifier among the fields returned by the SpecificFinder MethodInstances of the external items.