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# Historical Sessions

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By default, a session represents a view of the most current version of objects, and when you execute a query in that session, it returns the most current version of selected objects.

If your data source maintains past versions of objects, you can configure TopLink to access this historical data so that you can express read queries conditional on how your objects are changing over time. You can also do the following:

- Make series of queries relative to any point in time–not just the time of the first query.

- Provide read consistency so that a series of read operations or report queries all execute as if at the same time.

- Use the `mergeClone` method to provide deep recovery of an object by passing in a past version of it.

In addition, you can express query selection criteria as either of the following:

- A condition at a past time: for example, "employees who used to...".

- A change over time: for example, "employees who recently...".

For more information, see the following:

- "Historical Session Limitations"

- "Configuring Historical Sessions"

- "Acquiring a Historical Session"

- "Historical Queries".