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# Projects and Sequencing

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An essential part of maintaining object identity (see "Cache Type and Object Identity") is sequencing: managing the assignment of unique values to distinguish one instance from another.

Projects have different sequencing requirements, depending on their types:

- For relational projects, you typically obtain object identifier values from a separate sequence table (or database object) dedicated to managing object identifier values (see "Understanding Sequencing in Relational Projects").

- For EIS projects, you typically use a returning policy (see "Configuring Returning Policy") to obtain object identifier values managed by the EIS data source.

- For XML projects, because you are simply performing transformations between objects and XML documents, sequencing is not an issue.

To configure sequencing, you must configure:

- How to obtain sequence values (see "Configuring how to Obtain Sequence Values"), and

- Where to write sequence values when an instance of a descriptor's reference class is created (see "Configuring Where to Write Sequence Values")

Depending on the type of sequencing you use and the architecture of your application, you may consider using a sequence connection pool. For more information, see "Sequence Connection Pools".