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' 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.x, preface the behavior with the notation «selection» or «transformation».

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• Activity Diagram
• Activity
• SysML Activity Toolbox
• Object Flow
  

OMG UML Specification:

The OMG Unified Modeling Language specification, (v2.5.1, p.399) states:

A DataStoreNode is a CentralBufferNode that holds its object tokens persistently while its activity is executing. When an offer for an object token held by a DataStoreNode is accepted by a downstream object node, the offered token is removed from the DataStoreNode, per the usual CentralBufferNode semantics. However, a copy is made of the removed object token, with the same value, and this is immediately placed back onto the DataStoreNode. Thus, the values held by a DataStoreNode appear to persist for the duration of each execution of its containing activity, even as tokens move downstream from the node. When a DataStoreNode accepts an object token, if that token contains an object with the same identity as an object contained in a token already held by the node, then the duplicate object token shall not be placed on the DataStoreNode. Unlike a regular CentralBufferNode, a DataStoreNode contains objects uniquely.