Module 4: Relationships

1. Module 4: Relationships CS6359.0T1: Module 4

2. Overview • Relationships • Dependency • Generalization • Association • Realization (See Module 2 for this) • Modeling Techniques CS6359.0T1: Module 4

3. Relationships and Associations different words, but more or less same concept • UML • Associations • Fusion • Relationships • OMT • Associations CS6359.0T1: Module 4

4. Window open() close() Relationships: 3 Kinds Event dependency generalization ConsoleWindow DialogBox Control association CS6359.0T1: Module 4

5. Dependency • A change in one thing may affect another. • “Uses” relationship. • May have a name, but not common. AudioClip name Microphone record(m:Microphone) start() stop() dependency One important use of dependency CS6359.0T1: Module 4

6. Generalization • Relationship between general thing (parent) and more specific thing (child) • Child “is-a-kind-of” parent. • Child inherits attributes and operations of parent. generalization Shape base class Rectangle Circle Polygon leaf class Square CS6359.0T1: Module 4

7. Professor Course Associations (UML) • Represent conceptual relationships between classes direction indicator:how to read relation name relationship name teaches 1..* * teacher class role names • Multiplicity • defines the number of objects associated with an instance of the association. • Default of 1; • Zero or more (*); • n..m; range from n to m inclusive CS6359.0T1: Module 4

8. teaches Associations - In Other OOAD Associations may be binary, ternary, or higher order binary association Professor Course Fusion Style Ternary association Language Project Person How are these represented in UML? CS6359.0T1: Module 4

9. Associations – A Question • How would you model the following situation? “You have two files, say Homework1 and MyPet, where Homework1 is accessible only by you, but MyPet is accessible by anybody.” You could create two classes, File and User. Homework1 and MyPet are files, and you are a user. Approach 1: Now, would you associate the file access right with File? Approach 2: Or, would you associate the file access right with User? CS6359.0T1: Module 4

10. Associations – Links UML has links and associations whose ideas originate largely from OMT and also from Fusion to a certain extent. • OMT has links • link is a physical or conceptual connection between object instances. E.g., MyPet “is-accessible-to” by any user. • OMT has association • describes a group of links with common structure and common semantics • Inherently bi-directional • Often implemented as pointers in programming languages In other advanced OOAD notations, such as RML (Requirements Modeling Language), relationships including associations are treated fully and uniformly as classes. And as such they can have links as instances. CS6359.0T1: Module 4

11. Worker +setSalary( s : Salary) +setDept( d : Dept) Associations – UML Links • link is a semantic connection among objects. • A link is an instance of an association. association class class association name Company * 1..* works for employee employer w : Worker assign(development) : Company link Anonymous object Named object CS6359.0T1: Module 4

12. Associations – Link Attributes • Link Attributes The most compelling reason for having links and attributes is for-many-to-many relationships File User link attribute access permission • UML Association Class 1..* File User * class class AccessRight access permission association class CS6359.0T1: Module 4

13. Associations- Aggregation • structural association representing “whole/part” relationship. • “has-a” relationship. whole part multiplicity 1..* Company Department association aggregation CS6359.0T1: Module 4

14. Modeling Techniques • Simple dependencies • Single inheritance • Structural relationships CS6359.0T1: Module 4

15. Modeling Simple Dependencies • The most common dependency between two classes is one where one class uses another as a parameter to an operation. Create dependency pointing from class with operation to parameter. Using relationship CourseSchedule addCourse(c : Course) removeCourse(c : Course Course Usually initial class diagrams will not have any significant number of dependencies in the beginning of analysis but will as more details are identified. CS6359.0T1: Module 4

16. Modeling Single Inheritance • Look for common responsibilities, attributes, and operations that are common to two (2) or more classes. • If necessary, create a new class to assign commonalities. • Specify that the more-specific classes inherit from the more-general. In UML, abstract classes and their operations would be italicized. But not in Rational Rose Security presentValue() history() abstract is-a-kind-of relationship CashAccount Stock Bond interestRate presentValue() presentValue() presentValue() PreferredStock CommonStock CS6359.0T1: Module 4

17. Modeling Single Inheritance (cont’d) • Abstract • Abstraction—the essential characteristics of a thing. • Abstract class—cannot be instantiated. • Abstract method—has no implementation defined (i.e., no method body). • Depicted in italics or with stereotypes. • Concrete • Not abstract. • Can have instances. CS6359.0T1: Module 4

18. Modeling Structural Relationships • Considering a bunch of classes and their association relationships 1 0..1 School Department has 1..* 1..* 1..* 1..* 5 assigned to 5 member * 1..* 1..* 1 chairperson * 1..* 4 3 attends teaches Student Course Instructor * * The model above is from Rational Rose. How did the composite symbol ( )get loaded versus the aggregation?Use the Role Detail and select aggregation and then the “by value” radio button. CS6359.0T1: Module 4

19. Modeling Structural Relationships Composite Aggregation Body Car Liver Heart Wheel Engine Composite is a stronger form of aggregation. Composite parts live and die with the whole. CS6359.0T1: Module 4

20. Modeling Structural Relationships • Specify an association to create a navigation path between two objects (in either direction). • Specify an association if two objects interact with each other beyond operation arguments. • Specify multiplicity; 1 is assumed.(Error in text on implicit default.) • Specify aggregation when one of the classes represents a whole over the other classes. • How do you know that objects of one class must interact with another class? • Review the scenarios that were derived from Use Cases. • CRC cards seem much less used in practice.. CS6359.0T1: Module 4

21. Hints & Tips • Modeling relationships • Use dependencies when relationship is not structural. • Use generalization with “is-a” relationship. • Don’t introduce cyclical generalizations. • Balance generalizations - Not too deep, not too wide. • Use associations where structural relationships exist. • Drawing a UML relationship • Use rectilinear or oblique lines consistently. • Avoid lines that cross. • Show only relationships necessary to understand a particular grouping of things. • Elide redundant associations. CS6359.0T1: Module 4

22. Summary • Relationships • Dependency • Generalization • Association -Links and Link Attributes -Aggregation • Modeling techniques • Simple dependencies • Single inheritance • Structural relationships CS6359.0T1: Module 4

23. Points To Ponder • Show that cyclical generalizations lead to symmetric relationships between two classes. Use a couple of examples. • Why are cyclical generalizations not desirable? • Show that associations do not lead to transitive relationships but aggregations do. Use a couple of examples. • Express compositions using FOL (first-order logic). • Show that two classes C1 and C2 can be such that C2 is a subclass of C2 but at the same time C2 is an aggregation of C1. Use a couple of examples. • Show that two association classes can be related to each other, for example, through an association. • Can you give a counter-example to the statement “Composite parts live and die with the whole”? Or when would the statement not hold? CS6359.0T1: Module 4