2.3. Persistence Definition Language (PDL)

Because of the flexibility of both relational and object models, it is possible to map a given object model to many different relational models and to map a single relational model to many different object models.

WAF persistence uses a modeling and mapping language called Persistence Definition Language (PDL) to allow developers to describe their object model, their relational model, and how the two are mapped.

The metadata described in PDL allows the relational engine to efficiently persist changes to the object model and to construct efficient SQL queries for performing object-level reads. PDL also allows developers to define their own custom queries and SQL operations to do specialized querying and updating of the relational model.

For a listing of PDL terms, see Appendix D PDL Syntax. Examples of PDL usage can be found in Chapter 9 Persistence Tutorial.