1. A computer-readable medium containing a program, which when executed on a computer system performs an operation for accessing data stored in an underlying physical database, comprising: receiving a user request to perform a model entity operation, wherein the user request includes a user selection of a first instance of a model entity selected from a plurality of instances of the model entity included in a first query result and a selected query operation, wherein the model entity is defined by a database abstraction model logically describing an underlying database and wherein the model entity defines a focus for the selected query operation, and wherein instances of the model entity are distinguished by an identifier in an underlying database; retrieving, in response to the user request, a linking function configured to identify instances of the model entity that are related to the first instance of the model entity, according to a predefined relationship; and performing the model entity operation by: invoking the linking function to retrieve any instances of the model entity that are related to the first instance of the model entity; executing the selected query operation against the retrieved instances of the model entity, and; returning, as a second query result, at least a second instance of the model entity that satisfies any conditions specified by the selected query operation.