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# Configuring an EIS Descriptor as a Root or Composite Type

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You can designate an EIS descriptor as root (see "EIS Root Descriptors") or composite (see "EIS Composite Descriptors").

When you designate an EIS descriptor as a root, you tell the TopLink runtime that the EIS descriptor's reference class is a parent classš–no other class will reference it by way of a composite object mapping or composite collection mapping. Using an EIS root descriptor, you can configure all supported mappings and you can configure the descriptor with EIS interactions (see "Using EIS Interactions"). However, if you configure the EIS root descriptor with a composite object mapping or composite collection mapping, the reference descriptor you define must be an EIS composite descriptor; it cannot be another EIS root descriptor.

When you designate an EIS descriptor as a composite (the default), you tell the TopLink runtime that the EIS descriptor's reference class may be referenced by a composite object or composite collection mapping (see Configuring an EIS Composite Object Mapping and Configuring an EIS Composite Collection Mapping). Using an EIS composite descriptor, you can configure all supported mappings, but you cannot configure it with EIS interactions.

You can configure inheritance for a descriptor designated as a composite (see "Configuring Inheritance for a Child (Branch or Leaf) Class Descriptor"), however, in this case, all the descriptors in the inheritance tree must be aggregates. Aggregate and class descriptors cannot exist in the same inheritance tree. For more information, see "Aggregate and Composite Descriptors and Inheritance".

If you configure a descriptor as a composite using TopLink Workbench, you cannot configure the descriptor with EJB information (see "Configuring a Descriptor With EJB Information").

For more information, see the following:

- "Descriptors and Aggregation"

- "Composite and Reference EIS Mappings"