CS3773 Software Engineering

1. CS3773 Software Engineering Lecture 04 UML Class Diagram

2. Class and Object • Objects are discrete entities with well defined boundaries and encapsulate • States • Behaviors • Classes represent types of objects that share a set of features: attributes, operations, and relations • Classes describe key concepts involved in the problem domain • Classes are basic building blocks of OO system UTSA CS3773

3. UML Class Diagram Syntax • Elements of class diagram: • Class represented as a box containing three compartments • Name • Attributes • Operations • Relation represented as a line between two classes • Association • Generalization • Aggregation and composition UTSA CS3773

4. Class Diagram: Perspectives • UML class diagrams can be used in three distinct ways depending on the phase of system development: • Conceptual (Domain Models) • Requirements phase • The diagram represents the problem that the software should solve • Classes are real-world concepts in the system's environment • Not necessarily a direct mapping to how these will be implemented (although they may end up being classes in the software system) UTSA CS3773

5. Class Diagram: Perspectives • Design • The diagram is complete: both attributes and operations • The diagram depicts only the interfaces of software classes, but still avoids implementation details (information hiding) • Implementation • The diagram depicts interfaces and implementations of classes UTSA CS3773

6. Class • Classes are entities from the problem domain • Actors that interact with system • Any information that the system stores, analyzes, transforms, displays, etc. • Transient objects e.g., business transactions, phone conversations, etc. • Classes are named, usually, by short singular nouns • Syntax: A box with three compartments for names, attributes, and operations respectively UTSA CS3773

7. Class Diagram – An Example Class Diagram – An Example UTSA CS3773

8. Identifying Class • Classes are usually derived from the use cases for the scenarios currently under development • Brainstorm about all the entities that are relevant to the system • Noun Phrases • Go through the use cases and find all the noun phrases • Watch out for ambiguities and redundant concepts UTSA CS3773

9. Attribute • Attributes are simple data associated with a class e.g., integer, sets, dates • Attributes are properties of a class • Attributes are information that distinguishes one instance of the class from another instance • They are distinguishing characteristics of the objects • Syntax: name: type = default value UTSA CS3773

10. Operation • Operations are the responsibilities/services of an object in the class • Operations query or transform values of object's attributes, change state • A class's attributes and operations document the purpose of the class --- what information it maintains, and how that information can be manipulated • Syntax: name (parameters) : return-type UTSA CS3773

11. Static Attribute and Operation • Static attributes model data values shared by all objects of the class e.g., number of objects • Static operations are class-related operations not offered by instances of the class e.g., “create ()”, “search ()” • Syntax: underlined attribute or operation UTSA CS3773

12. Association • An association is a relationship between classes • An association is a name, usually short verb • Some people name every association • Others name associations only when such names will improve understanding e.g., avoid names like “is related to”, and “has” • An association represents different types of relationships e.g., data flow, requests, parts of compound class UTSA CS3773

13. Association Syntax • An association may have • An association name • Multiplicity • Role names • Qualifier • Association class • Navigability UTSA CS3773

14. Multiplicity • Multiplicities on associations give lower and upper bound on the number of instances of the local class that can be linked to one instance of the remote class • Syntax: 1, *, etc. at the association end. Examples: • * (zero or more) • 1 .. * (one or more) • 1 .. 40 (one to 40) • 5 (exactly 5) • If no multiplicity is specified, the default is 1 UTSA CS3773

15. Multiplicity • Multiplicities on classes indicate how many instances of the class can be at run time • Multiplicities constrain the number of objects • Syntax: 1, *, etc. at the top right corner of class UTSA CS3773

16. Role Name • Is a part of association • Describes how the object at the association end is viewed by the associated object • Is useful for specifying the context of the class • Syntax: name at the association end UTSA CS3773

17. Qualified Association • Qualified association is an association key that identifies the object at the other end of the association • Qualifier is a key or index used to identify one or fewer objects from set of many objects • Qualifier is often an attribute of the class at the other end of the association, and the attribute is recognized as uniquely identifying one or fewer objects of the class. • Syntax: name in box at the end of an association UTSA CS3773

18. Association Class • Association class allows to add attributes, operations to an association • The association contains more information • Syntax: class connected to the association by a dashed line • Constraint: only one instance of association class between any two associated objects UTSA CS3773

19. Generalization • Indicates an “is-a” relationship • All instances of the subclass are instances of the super class • A subclass inherits all attributes, operations and associations of the parent • The common attributes and operations are placed in the superclass; subclasses extend the attributes, operations, and associations as they need them • Syntax: open triangle at the superclass end of the association UTSA CS3773

20. Aggregation • Indicates a loose “has-a” relationship • The compound class is made up of its component classes • Represents the “whole-part” relationship, in which one object consists of the associated objects • The whole controls the relationship • The part services requests from the whole • Syntax: hollow diamond at the compound class end of the association UTSA CS3773

21. Aggregation Semantics • Whole can exist independently of the parts • Part can exist independently of the whole • Whole is incomplete if some of the parts are missing • It is possible to have shared ownership of the parts by several wholes UTSA CS3773

22. Composition • Composition is a particular kind of aggregation • Component classes are physically part of the compound class e.g., a car is composed of an engine, wheels, etc. • The component class dies if the compound class dies • Syntax: filled diamond at the compound class end of the association UTSA CS3773

23. Composition Semantics • Component belong to exactly one compound at a time • Compound is responsible for the creation and destruction of all its components • Compound may also release its components to other compounds • If the compound is destroyed, it must either destroy all its components, or give responsibility for them over to some other classes UTSA CS3773

24. Review of Class Diagram • Class is a set of discrete entities that share the same features • Class encapsulates data (attributes) and functions (operations: queries of modifiers) • Multiplicity constrains the number of objects participating in a relationship at any point in time • Relationship represents connections between classes • Association: role name, qualifier, association class, navigability • Generalization • Aggregation and composition UTSA CS3773

25. UML Object Diagram • Object is an instance of some class • Object diagram is a snapshot of the objects in a system • Object diagram represents all the instances of classes (objects) and their associations (links) at a point of time • Object diagram gives better feeling of problem by showing examples UTSA CS3773

26. UML Object Diagram Syntax • Object is a box with two compartments: object name and attributes • Objects name is underlined • Class name alone • Object name alone • Object name concatenated with the class name, separated by a colon • Name convention: starting with a lowercase letter • Relations among objects are represented as links UTSA CS3773

27. UML Object Diagram – An Example A: Book Ann: Patron : Book1 Jo: Patron : Book2 Tom: Patron : Book UTSA CS3773

28. Reading Assignments • UML 2 and The Unified Process • Chapter 7, “Objects and classes” • Chapter 8, “Finding analysis classes” • Chapter 9, “Relationships” • Chapter 18, “Refining analysis relationships” UTSA CS3773