1. A method of utilizing a schema for defining a join relationship, the schema being utilized for merging a database part table with a database table by a database application executing on a computer system, comprising: receiving, in the database application, target table metadata associated with a database part in a plurality of relationship elements in the schema, the database part comprising a target table; receiving, in the database application, source table metadata associated with a database comprising a source table to be joined with the target table in the plurality of relationship elements in the schema, the source table metadata describing a relationship to a class of tables existing outside of the target table; receiving, in the database application, join type metadata in the plurality of relationship elements in the schema, the join type metadata defining how data in the target table is to be merged with data in the source table; and in response to receiving the target table metadata and the source table metadata, merging the target and source tables utilizing the join type metadata.