Aspects of the subject matter described herein relate to mapping from application objects to an abstract data model. In aspects, a mapper receives registrations that indicate behavior (e.g., how objects are constructed, modified, or examined) of application objects. The behavior may be specified using user-supplied expressions. The mapper aggregates this data and uses it to map application requests for data access into one or more operations that operate on the abstract data model. A data access layer may then translate the operations into actions to access data corresponding to the requests from a store. If appropriate, data obtained from the store may then be inserted into application objects as indicated by the registrations.