In computer science, persistence refers to the characteristic of data that outlives the execution of the program that created it. Without this capability, data only exists in RAM, and will be lost when the memory loses power, such as on computer shutdown.
Computer programming
In programming, persistence refers specifically to the ability to retain data structures between program executions, such as, for example, an image editing program saving complex selections or a word processor saving undo history.
This is achieved in practice by storing the data in non-volatile storage such as a file system or a relational database or an object database. Design patterns solving this problem are container based persistence, component based persistence and the Data Access Object model. When first introduced, the idea was that persistence should be an intrinsic property of the data, in contrast with the traditional approach where data is read and written to disk using imperative verbs in a programming language. This emphasis has largely disappeared, resulting in the use of persist as a transitive verb: On completion, the program persists the data. Examples of persistence are using Java serialization to store Java objects on disk or using Java EE to store Enterprise Java Beans in a relational database.
Persistence Services
Persistence services is when the workflow runtime engine semantics dictate that persistence should occur, the workflow runtime engine will call methods supplied by a persistence service to save state information about the workflow instance. Likewise when workflow runtime engine needs to restore a previously persisted workflow instance, it will call methods supplied by the persistence service to load this state information.
Reference:
http://en.wikipedia.org/wiki/Persistence_(computer_science)
