Common Mechanisms of UML

Advanced Classes 

Classifiers  Visibility  Scope  Multiplicity  Attributes  Operations  Template Classes  Standard Elements Common Modeling Techniques

Classifiers: 

A classifier is a mechanism that describes structural and behavioral features 

In general, the modeling elements that can have instances are called classifiers 

Class, Instance, Component, Node, Use case, Subsystem are classifiers 

Class: A set of attributes, operations, relationships and semantics 

Use case: Set of a sequence of actions, including variants, that a system performs that yields an observable result or value to a particular actor 

Datatype: A type whose values have no identity, including primitive built-in types (such as numbers anti strings), as well as enumeration types (such as Boolean) 

Component: Physical and replaceable part of a system that conforms to and provides the realization of a set of interfaces 

Node: A physical element that exists at run time and that represents a computational resource, generally having at least some memory anti often processing capability 

Subsystem: Grouping of elements of which some constitute a specification of the behavior offered by the other contained elements

Visibility: 

Public [+]: All outside classifiers that have visibility to the given classifier, can use this feature 

Protected [#]: All descendants of the classifier can use the feature 

Private [-]: The classifier alone can use the feature

Scope: 

The owner scope of a feature specifies whether the feature appears in each instance of the classifier or whether there is just a single instance of feature for all instances of the classifier. 

• Instance: Each instance holds its own value 
• Classifier: Just one value for all instances (static)

Multiplicity: 

Typically, there may be any number of instances of classes 

The number of instances a class may have is called multiplicity 

Attributes: 

The syntax of an attribute in the UML is: 

[visibility] name [multiplicity] [: type] [=initial-value] [{property-string}] 

There are three defined properties: 

• Changeable: There are no limitations on modifying the value of the attribute
• AddOnly: Additional value may be added for attributes that have a multiplicity > 1. Existing value may not be altered or removed 
• Frozen: The value of attribute may not be altered after an object is initialized

Operations: 

• The syntax of an operation in UML is 
• [visibility] name [(parameter-list)] [: return-type] [{property-string}] [direction] name: type [=default-value] 
• There are five defined properties: 

Leaf: May not be overridden  isQuery: Leave the state of subsystem unchanged  Sequential: Only one flow is in the object at a time  Guarded: Sequentializing all calls  Concurrent: Treating the operation as atomic

Template Classes: 

• These are similar to the template classes in C++ and Ada 
• Cannot use a template directly; first it should be instantiated

Standard Elements: 

The standard stereotypes that apply to classes are:

• Metaclass: A classifier whose objects are all classes 
• Powertype: A classifier whose objects are classes, which are the children of a given parent class 
• Stereotypes: A stereotype that may be applied to other elements 
• Utility: A class whose attributes and operations are all static scoped so that the clients of utility may not necessarily create instances to use the operations and attributes