Architecting and designing : UML 2.0 Lite : UML models : UML class diagrams : Persistence
  
Persistence
Persistence describes a classes ability to exist. A persistent class is one that exists through runtime. It can be viewed as a table-like structure that can hold data and maintain information. Only classes designated as persistent are mapped to entities in an Entity Relation (ER) data model diagram.
A transitory class is one that only exists temporarily during runtime. It is not mapped to an entity in an ER diagram.
See also
UML class diagrams