The Structure of the Deployment Descriptor
The deployment descriptor in EJB 2.0 has a major new section to support the new model of entity
persistence. It provides for the description of the relationships between entity objects. Here is a table
providing short descriptions of the major "top-level" elements of the EJB 2.0 deployment descriptor, and
what has changed that is relevant to EJB 2.0 persistence:
| Element |
Description |
| <enterprise-beans> |
This is the section where EJB components (session beans, message-
driven beans, and entity beans) are described. The description for
container-managed entity beans will include their container-
managed fields. If the entity uses the EJB 2.0 model of container-
managed persistence, it will also provide a name for the entity's
schema and the EJB QL queries for its finder and ejbSelect()
methods. |
| <relationships> |
The relationships section of the deployment descriptor
describes the relationships between entity beans using EJB 2.0,
that are described in this deployment descriptor. Each
relationship has two relationship roles, specifying the
multiplicity, role source, cmr field if necessary, type of role
collection if necessary, and cascade-delete if necessary. |
| <assembly-descriptor> |
The application assembly information describes how the EJB
component or components are composed into a larger
application unit. The EJB 2.0 specification introduces the
concept of unchecked methods, which helps to make fine-
grained entities practical for your object model. |
| <ejb-client-jar> |
The ejb-client-jar specifies an archive that contains the
Java class files necessary for a client program to use the EJB
components in this JAR. This section does not introduce
anything relevant to EJB 2.0 persistence. |
Of course, the entity element of the deployment descriptor changed to support the changes in EJB
2.0. The following diagram, produced using XMLSpy, shows the sub-elements of the deployment
descriptor's entity element:
The <local> and <local-home> elements have been added to support local interfaces, and the
<home> and <remote> elements have been made optional to handle the (likely) case that only local
interfaces are specified. The <abstract-schema-name> element has been added to support abstract
schemas in queries, and the <query> element has been added to specify EJB-QL syntax for
ejbSelect() and finder methods.
Likewise, here is the visualization for the <relationships> element:
We'll be looking at the deployment descriptor for relationships in great detail in the next chapter.
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