UML Class Diagrams advanced concepts

1. UML Class Diagrams advanced concepts 14 October 2010

2. 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

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

4. (Multiple) Objects Property of object = attribute + value 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

5. Connection between Objects Link = connection between objects 1247: Customer Custno = 1247 Name = Adacs Address = Enschede 345T7: Order Orderno = 345T7 dateReceived = 10/10/05 Price = 1987 902U2: Order Orderno = 902U2 dateReceived = 07/04/05 Price = 3789

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

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

8. 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

9. 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.

11. 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.

12. employee employer Person Company works for employee employer Person Company  has employment for 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).

13. transports Car Person passenger transports 5 Car Person passenger transports * Car Person passenger transports 1..* Car Person passenger transports 2..5 Car Person passenger 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

15. 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

16. 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.

17. 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

19. 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 { }.

21. 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.

22. 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.

23. Aggregation and Composition: example

24. 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.

25. Object diagram: example

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

27. 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.

28. Advanced Class Features

29. 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.

30. 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.

31. 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.

32. 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.

33. Advanced Class Concepts : Abstract cont.

34. 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.

35. Window as Abstract Class

36. 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.

37. Lollipop notation for Interfaces

38. 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}

39. Aggregation and Composition once more, cont.

40. Aggregation and Composition: Example

41. Alternative notation for Composition

42. 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.

43. Derived Associations and Attributes example

44. 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.

45. Relations and Constraints

46. subdirectory 0..* • 0..* Directory File 0..1 parent Reflexive Associations • A class has an association to itself. • Example: A directory may contain other directories.

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

48. Constraints

49. References • Sommerville, Ian (2001) Software Engineering, 6th edition http://www.software-engin.com • Grady Booch, James Rumbaugh, Ivar Jacobson (2005) The Unified Modeling Language User Guide, 2nd edition • Martin Fowler (2000, 2004) Object-Oriented Software Engineering, 2nd edition; 3rd edition

50. 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?