Datastore

Description

A Datastore is an element used to define permanently stored data. A token of data that enters into a Datastore is stored permanently, updating tokens for data that already exists. A token of data that comes out of a Datastore is a copy of the original data.

Use Object Flow connectors to connect elements (such as Activities) to Datastores, as values and information are being passed between nodes. Selection and transformation behavior, together composing a sort of query, can be specified as to the nature of data access. For instance, selection behavior determines which objects are affected by the connection to the Datastore. Transformation behavior might then further specify the value of an attribute pertaining to a selected object.

To define the behavior of access to a Datastore, attach a note to the Object Flow connector. To do this, right-click on the Object Flow and select the Attach Note or Constraint context menu option. A dialog indicates other flows in the Activity diagram, to which you can attach the note (if the behavior applies to multiple flows). To comply with UML 2, preface behavior with the notation «selection» or «transformation».

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OMG UML Specification:

The OMG UML specification (UML Superstructure Specification, v2.1.1, p. 360) states:

A data store node is a central buffer node for non-transient information... A data store keeps all tokens that enter it, copying them when they are chosen to move downstream. Incoming tokens containing a particular object replace any tokens in the object node containing that object.