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Glossary Page



An entity with a well-defined boundary and identity that encapsulates state and behavior. State is represented by attributes and relationships, behavior is represented by operations, methods and State Machines. An Object is an instance of a Class.

See also: class, instance

object diagram

A diagram that encompasses objects and their relationships at a point in time. An Object diagram can be considered as a special case of a Class diagram or Communication diagram.

See also: class diagram, communication diagram

object flow

A sub type of the State flow or transition. It implies the passing of an object instance between elements at run-time.

object flow state

A state in an Activity graph that represents the passing of an object from the output of actions in one State to the input of actions in another State.

object lifeline

A line in a Sequence diagram that represents the existence of an object over a period of time.

See also: sequence diagram

Object Management Group (OMG)

The standards body responsible for the UML specification and management. Their website is - follow the links to the UML pages.


A relationship that indicates that a Collaboration represents a classifier. An Occurrence connector is drawn from the collaboration to the classifier.


A service that can be requested from an object to effect behavior. An operation has a signature, which could restrict the actual parameters that are possible.