UML Class Diagram

Class Diagram⌘

Describes the structure of a system by showing the system's classes, their attributes, and the relationships among the classes.

Classifier⌘

• an abstract base class
• describes a set of instances that have features in common

Feature⌘

• declares a behavioral or structural characteristic of instances of classifiers
• structural feature describes a structure of an instance of a classifier (e.g. property)
• behavioral feature specifies an aspect of the behavior of classifier's instances (e.g. operation)

Property⌘

• Properties are Structural Features that represent:
  • the attributes of Classifiers (when a property is owned by a Classifier other than an Association)
  • the member Ends of Associations
  • the parts of Structured Classifiers.

Operation⌘

• a behavioral feature of a classifier, which specifies name, type, parameters, and constraints
• can have preconditions and postconditions
• can have a type (the type of the return parameter)
• example:

+ createWindow (location: Coordinates): Window

Class⌘

• describes a set of objects that share the same specifications of features (attributes and operations)
• is a special classifier
• an object is an instance of a class

Generalization⌘

• relationship between a more general classifier and a more specific classifier
• each instance of the specific classifier is also an indirect instance of the general classifier
• the specific classifier inherits the features of the more general classifier

Generalization Example⌘

Association⌘

• specifies a relationship between instances
• describes a set of tuples whose values refer to typed instances
• declares that there can be links between instances of the associated types

Multiplicity⌘

• specifies how many objects of the opposite class an object can be associated with
• is a range of the minimum and maximum values
• syntax: number or min..max

Multiplicity	Notation
zero	0 or 0..0
exactly one	1
zero or one	0..1
zero or more	0..* or *
one or more	1..*

Multiplicity example⌘

Multiplicity - order and uniqueness⌘

• Multiplicity defines a specification of order and uniqueness of the collection elements.
• This option can specify whether the values should be unique and/or ordered.
  • ordered: the collection of values is sequentially ordered (default: not ordered)
  • unique: each value in the collection of values must be unique (default: is unique)

Property = End or Attribute⌘

Navigability⌘

• specifies whether one object can be accessed directly from another

Aggregation⌘

• shows how something (whole) is composed of parts
• parts can exist separately - can be shared
• precise semantics of aggregation varies by application area and modeler :)

Composition⌘

• a strict form of aggregation
• the whole is the owner of its parts
• parts can not be shared
• the existence of its parts depends on the whole

Aggregation / Composition Example⌘

N-ary association⌘

• if an association has more than two end points (here: ternary association)
• Notation: a rhombus is used as a connection point

Association Class ⌘

• Association Class ia a model element that has both Association and Class properties.
• It not only connects a set of Classifiers but also defines a set of Features that belong to the Association itself.

Dependency ⌘

• a relationship that signifies that a model element(s) requires other model element(s) for their specification or implementation
• the complete semantics of the depending elements is dependent on the definition of the supplier element(s)
• the modification of the supplier may impact the client model elements
• the semantics of the client is not complete without the supplier
• the type of dependency can be specified by using a keyword or stereotype

Interface⌘

• is a kind of classifier that represents a declaration of a set of coherent public features and obligations
• an interface specifies a contract; any instance of a classifier that realizes the interface must satisfy that contract
• it is just declaration - so it is not instantiable

Provided Interface⌘

• an interface realized by a classifier is its provided interface
• represent the obligations that instances of that classifier have to satisfy

Required Interface⌘

• specify services that a classifier needs in order to perform its function

Interface Example⌘

Named Element⌘

• represents an element that may have a name and a visibility

Visibility Kind	Notation
public	+
private	-
protected	#
package	~

Package⌘

• used to group elements, and provides a namespace for the grouped elements
• qualified name:

package name::element name

Package Import, Access⌘

A package import is defined as a directed relationship that identifies a package whose members are to be imported by a namespace.

Two types:

• «import» for a public package import
  • transitive: if A imports B and B imports C then A indirectly imports C
• «access» for a private package import
  • intransitive

Package Import Example⌘

• elements in Types are imported to ShoppingCart, and then further imported to WebShop
• elements of Auxiliary are only accessed from ShoppingCart, and cannot be referenced from WebShop

Instance ⌘

• is a concrete instance in the modeled system
• instance = object

Comment⌘

• a textual annotation that can be attached to an element
• may contain information that is useful to a modeler
• can be attached to more than one element

Constraint⌘

• condition or restriction related to an element
• it must always be true
• can be in a formal (OCL) or in a human language
• syntax:

{ [name :] boolean expression }