7M822 UML Class Diagrams advanced concepts 14 October 2010

7M822 UML Class Diagrams The class diagram provides a static structure of all the classes that exist within the system. Classes are arranged in hierarchies sharing common structure and behaviour and are associated with other classes. Class diagrams are used in: Analysis To build a conceptual domain model with semantic associations between concepts Design Structural model of a design in terms of class interfaces Implementation Source code documentation, exposing the implementation 2

7M822 An object is a thing that can be tangible or intangible. Examples tangible : bike, car, house intangible : order, account Objects An object has properties. Example a Customer has a name and address Customer Name Address 3

7M822 Property of object = attribute + value (Multiple) Objects Adacs: Customer Name = Adacs Address = Enschede Primo: Customer Name = Primo Address = Grave Multiple objects  unique identity 1247: Customer Custno = 1247 Name = Adacs Address = Enschede 9378: Customer Custno = 9378 Name = Primo Address = Grave 4

7M822 Link = connection between objects Connection between Objects 1247: Customer Custno = 1247 Name = Adacs Address = Enschede 345T7: Order Orderno = 345T7 dateReceived = 10/10/05 Price = U2: Order Orderno = 902U2 dateReceived = 07/04/05 Price =

7M822 Class class is abstract concept each object is instance of a class classes classify objects attribute has no values Class Customer Custno Name Address Order Orderno dateReceived Price Object analysis  than values to attributes 6

7M822 Attribute has no values Association is relation between classes Class Diagram Customer Custno Name Address Order Orderno dateReceived Price Link is instance of association 1 * 7

7M822 Class diagram A class diagram describes the type of objects in a system and the static relationships between them. Static relations: – Associations – Subtypes Static structure: – Attributes – Operations 8

7M822 Class – operations An operation is the implementation of a service that can be requested from any object of the class in order to affect behaviour. Operations are used to manipulate the attributes or to perform other actions. Operations are normally called functions, but they are inside a class and can be applied only to objects of that class. An operation is described with a return-type, a name and zero or more parameters. Together, the return-type, name, and parameters are called the signature of the operation. The signature describes everything needed to use the operation. 9

7M822 10

7M822 Class - associations Associations are structural relationships where instances (objects) of one class are connected to instances (objects) of another class. –an employee works for a company –a company has a number of offices An association is normally bidirectional, which means that if an object is associated with another object, both objects are aware of each other (navigation is bidirectional by default). Binary association connects exactly two classes. N-ary connects many classes. The most common association is just a connection between classes. 11

7M822 Association adornments: name, role The association has a name - the descriptive term, often a verb, for the association. Each association has two association ends; each end is attached to one of the classes in the association. An end can be explicitly named with a label. This label is called a role name (association ends are often called roles). PersonCompany employee employer works for PersonCompany employee employer  has employment for 12

7M822 Associations: multiplicity Multiplicity defines the number of objects associated with an instance of the association. –Default of 1 (1: 1) –0 or 1: 0..1 –Zero or more (0..infinite): * –1 or more (1..infinite): 1..* –n..m; range from n to m inclusive CarPerson transports passenger CarPerson transports passenger 5 CarPerson transports passenger * CarPerson transports passenger 1..* CarPerson transports passenger

7M822 14

7M822 Generalization A specialization / generalization relationship, in which objects of the specialized element (child) are substitutable for objects of the generalized element (parent). –Superclass – the generalization of another class, the child. –Subclass – the specialization of another class, the parent. Customer Corporate Customer Personal Customer 15

7M822 Generalization - characteristics Identify common features concerning behaviour and knowledge. Define these common features on a higher level in the inheritance hierarchy. The aim is at behaviour more than knowledge when combining classes. Generalization is a bottom-up process. A superclass includes all common properties of its subclasses. 16

7M822 Specialization - characteristics Define a new class which is a special appearance of an existing class. Specialization is a top-down process. A subclass can have attributes and operations that are specific for that sub-class. A subclass may redefine operations of its super-class 17

7M822 18

7M822 Constraints The basic constructs of association, attribute, and generalization do much to specify important constraints. They cannot indicate every constraint. These constraints still need to be captured; the class diagram is a good place to do that. The UML allows you to use anything to describe constraints. The only rule is that you put them inside braces { }. 19

7M822 20

7M822 Attribute analysis It is not always clear which attributes belongs to which classes by finding out the class attributes. An attribute is assigned to that class where it is certainly a feature. For example: a project leader has the attributes name, department and age. But what to do with the attributes project number, project duration, starting time, and budget? These attributes clarifies something about the relation between project leader and type of project. This often happens if a n:m relation refers to an association between two classes. In that case, we can define a new class, for instance project management. 21

7M822 Aggregation and Composition Aggregation is a special form of association that specifies a whole-part relationship between the aggregate (the whole) and a component (the part). Composition is a form of aggregation with strong ownership and coincident lifetime of the parts by the whole; parts with nonfixed multiplicity may be created after the composite itself, but once created they live and die with it; such parts can also be explicitly removed before the death of the composite. 22

7M822 Aggregation and Composition: example 23

7M822 Object diagram An object diagram is a diagram that shows a set of objects and their relationships at a point in time; object diagrams address the static design view or static process view of a system. An object diagram is shown as a class, and the name is underscored, although an object’s name can be shown optionally preceding the class name as: objectname: classname. The object does not have to be named, in which case only the classname is shown underscored. 24

7M822 Object diagram: example 25

7M822 Association Navigation Navigation across an association is, unless otherwise specified, bidirectional. Sometimes, you will want to limit navigation to just one direction. 26

7M822 Dependency Relationship A dependency exits between two elements if changes to the definition of one element (the supplier) may causes changes to the other (the client). With classes: one class sends a message to another; one class has another as part of its data; one class mentions another as a parameter to an operation. 27

7M822 Advanced Class Features 28

7M822 Advanced Class Concepts : Visibility Visibility – class members (attributes, operations) may be specified as: {we have feature f, an attribute or operation that is defined on an object O of class C } + : public {f is public  f is visible to any object and f is inherited by the subclasses of C.} # : protected (f is protected  f is visible only to objects of class C and to objects of C’s subclasses and f is inherited by the subclasses of C.} - : private {f is private  f is visible only to O and f is not inherited by the subclasses of C.} Restricting visibility is the same as restricting accessibility. 29

7M822 Advanced Class Concepts : Scope Individual member data (= attributes) may have: –Class scope : a single copy of an attribute is shared by all instances of a class. –Instance scope : each instance of a class would have its own copy of the attribute. 30

7M822 Class object Objects are abstractions of real-world entities. Objects encapsulate state and represent information. Object’s state is protected. Objects have responsibility. Objects interact by interfaces. 31

7M822 Advanced Class Concepts : Abstract An operation is abstract if it has no implementation. A abstract class cannot have any direct instances. Abstract classes only occur in the context of an inheritance hierarchy. Abstract operations and classes are specified by writing its name in italics. 32

7M822 Advanced Class Concepts : Abstract cont. 33

7M822 Interfaces and Abstract Classes One can vary the interfaces of classes independent of the implementation. A pure interface is a class with no implementation and, therefore has operation declarations but no method bodies an fields. Interfaces are often declared through abstract classes. 34

7M822 Window as Abstract Class 35

7M822 Interfaces and Abstract Class Sub classing is not only the way to do this. For instance Java provides an interface construct, and the compiler checks that the implementing class provides implementations of all the interface’s operations. 36

7M822 Lollipop notation for Interfaces 37

7M822 Aggregation and Composition once more Aggregation is a special form of association that specifies a whole-part relationship between the aggregate (the whole) and a component (the part); aggregation is the part-of relationship. { it is a special form of association in which a collection of objects, each having an independent existence, is associated with an single object} {unfilled diamond} Composition is a form of aggregation with strong ownership and coincident lifetime of the parts by the whole; the part object may belong to only one whole – the parts are usually expected to live and die with the whole. {usually, any deletion of the whole is considered to cascade to the parts}{filled diamond} 38

7M822 Aggregation and Composition once more, cont. 39

7M822 Aggregation and Composition: Example 40

7M822 Alternative notation for Composition 41

7M822 Derived Associations and Attributes Derived associations and attributes can be calculated fro other associations and attributes, respectively, on a class diagram. –For example, an age attribute of a Person can be derived if you know that Person’s date of birth. 42

7M822 Derived Associations and Attributes example 43

7M822 Qualified Associations The qualifier specifies how a specific object at the many end of the association is identified, and may be seen as a kind of key separating all the objects in the association. 44

7M822 Relations and Constraints 45

7M822 Reflexive Associations A class has an association to itself. Example: A directory may contain other directories. DirectoryFile 0..1 parent subdirectory 0..* 10..* 46

7M822 Exclusive-Or Associations Using an eclusive-or (xor) association constraint one can enforce that certain facts exclude each other. 47

7M822 Constraints ConstraintApplies to symbol Meaning complete generalization Specifies that all children in the generalization have been specified and that no additional children are permitted disjoint generalization Specifies that objects of the given parent may have no more than of the given children as a type incomplete generalization Specifies that not all children in the generalization have been specified and that additional children are permitted overlapping generalization Specifies that objects of the given parent may have more than one of the given children as a type xor association Specifies that, over a set of associations, exactly one is manifest for each associated object. 48

7M822 References Sommerville, Ian (2001) Software Engineering, 6 th edition Grady Booch, James Rumbaugh, Ivar Jacobson (2005) The Unified Modeling Language User Guide, 2 nd edition Martin Fowler (2000, 2004 ) Object-Oriented Software Engineering, 2 nd edition; 3 rd edition 49

7M822 Question ? Consider the class Patient and the subtyping of this class into the classes MalePatient and FemalePatient. - how looks the according class diagram, and - which constraint(s) could be mentioned? 50