Chapter Twelve

Abstract Class A class that has no direct instances, but whose descendants may have direct instances. See also Concrete class.
Abstract operation Defines the form or protocol of the operation, but not its implementation.
Activation The time period during which an object performs an operation.
Actor An external entity that interacts with the system (similar to an external entity in data flow diagramming). See also Use-case.
Aggregation A part-of relationship between a component object and an aggregate object. See also Composition.
Association A relationship between object classes. See also Association role.
Association class An association that has attributes or operations of its own, or that participates in relationships with other classes.
Association role The end of an association which connects it to a class. See also Multiplicity.
Asynchronous message A message in which the sender does not have to wait for the recipient to handle the message. See also Sequence diagram, Simple message, Synchronous message.
Behavior Represents how an object acts and reacts.
Class See also Object class.
Class diagram Shows the static structure of an object-oriented model: the object classes, their internal structure, and the relationships in which they participate.
Class-scope attribute An attribute of a class that specifies a value common to an entire class, rather than a specific value for an instance.
Component diagram Shows the software components or modules and their dependencies. See also Package.
Composition A part object that belongs to only one whole object and lives and dies with the whole. See also Aggregation.
Concrete class A class that can have direct instances. See also Abstract class.
Constructor operation An operation that creates a new instance of a class. See also Abstract operation, Query operation, Update operation.
Encapsulation The technique of hiding the internal implementation details of an object from its external view.
Event Something that takes place at a certain point in time; a noteworthy occurrence that triggers a state transition.
Method The implementation of an operation.
Multiple classification Shows that an object is an instance of more than one class.
Multiplicity Indicates how many objects participate in a given relationship.
Object An entity that has a well-defined role in the application domain and has state, behavior, and identity. See also Object class, Object diagram.
Object class (class) A set of objects that share a common structure and a common behavior. See also Abstract class, Concrete class.
Object diagram A graph of instances that are compatible with a given class diagram.
Operation A function or a service that is provided by all the instances of a class. See also Abstract operation, Constructor operation, Method, Polymorphism, Query operation, Update operation.
Overriding The process of replacing a method inherited from a superclass by a more specific implementation of that method in a subclass.
Package A set of cohesive, tightly coupled classes representing a subsystem. See also Component diagram.
Polymorphism The same operation may apply to two or more classes in different ways.
Query operation An operation that accesses the state of an object but does not alter the state. See also Abstract operation, Constructor operation, Update operation.
Sequence diagram Depicts the interactions among objects during a certain period of time.
Service See Method.
Simple message A message that transfers control from the sender to the recipient without describing the details of the communication. See also Asynchronous message, Sequence diagram, Synchronous message.
State Encompasses an object‚s properties (attributes and relationships) and the values those properties have. See also Behavior.
State diagram A model of the states of an object and the events that cause the object to change from one state to another.
State transition Changes in the attributes of an object or in the links an object has with other objects. .
Synchronous message A type of message in which the caller has to wait for the receiving object to finish executing the called operation before it can resume execution itself. See also Asynchronous message, Sequence diagram, Simple message.
Update operation An operation that alters the state of an object. See also Abstract operation, Constructor operation, Query operation.
Use case A complete sequence of related actions initiated by an actor, it represents a specific way of using the system.
Use-case diagram A diagram that depicts the use cases and actors for a system.

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