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Lawrence ChungCS6359.0T1: Module 41 Module 4: Relationships

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Lawrence ChungCS6359.0T1: Module 42 Overview Relationships Dependency Generalization Association Realization (See Module 2 for this) Modeling Techniques

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Lawrence ChungCS6359.0T1: Module 43 Relationships and Associations UML Associations Fusion Relationships OMT Associations different words, but more or less same concept

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Lawrence ChungCS6359.0T1: Module 44 Relationships: 3 Kinds Window open() close() ConsoleWindowDialogBoxControl Event association dependency generalization

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Lawrence ChungCS6359.0T1: Module 45 AudioClip Dependency A change in one thing may affect another. Uses relationship. May have a name, but not common. record(m:Microphone) start() stop() Microphone name dependency One important use of dependency

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Lawrence ChungCS6359.0T1: Module 46 Generalization Relationship between general thing (parent) and more specific thing (child) Child is-a-kind-of parent. Child inherits attributes and operations of parent. Rectangle Square PolygonCircle Shape base class leaf class generalization

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Lawrence ChungCS6359.0T1: Module 47 Associations (UML) ProfessorCourse teaches relationship name direction indicator: how to read relation name teacherclass 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 1..* * Represent conceptual relationships between classes

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Lawrence ChungCS6359.0T1: Module 48 Associations - In Other OOAD ProfessorCourse teaches Fusion Style binary association Ternary association Project Language Person Associations may be binary, ternary, or higher order How are these represented in UML?

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Lawrence ChungCS6359.0T1: Module 49 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?

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Lawrence ChungCS6359.0T1: Module 410 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.

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Lawrence ChungCS6359.0T1: Module 411 Associations UML Links link is a semantic connection among objects. A link is an instance of an association. Company 1..* * employee employer : Company assign(development) w : Worker link Named object Anonymous object class association class Worker +setSalary( s : Salary) +setDept( d : Dept) works for association name

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Lawrence ChungCS6359.0T1: Module 412 Associations Link Attributes Link Attributes The most compelling reason for having links and attributes is for-many-to- many relationships FileUser access permission FileUser access permission UML Association Class AccessRight * 1..* link attribute association class class

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Lawrence ChungCS6359.0T1: Module 413 Associations - Aggregation Company Department 1..* association multiplicity aggregation part whole - structural association representing whole/part relationship. - has-a relationship.

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Lawrence ChungCS6359.0T1: Module 414 Modeling Techniques Simple dependencies Single inheritance Structural relationships

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Lawrence ChungCS6359.0T1: Module 415 Modeling Simple Dependencies 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. Using relationship 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.

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Lawrence ChungCS6359.0T1: Module 416 Modeling Single Inheritance In UML, abstract classes and their operations would be italicized. But not in Rational Rose CashAccount presentValue() interestRate Security presentValue() history() Bond presentValue() Stock presentValue() PreferredStock CommonStock abstract is-a-kind-of relationship 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.

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Lawrence ChungCS6359.0T1: Module 417 Modeling Single Inheritance (contd) Abstract Abstractionthe essential characteristics of a thing. Abstract classcannot be instantiated. Abstract methodhas no implementation defined (i.e., no method body). Depicted in italics or with stereotypes. Concrete Not abstract. Can have instances.

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Lawrence ChungCS6359.0T1: Module 418 Modeling Structural Relationships 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. School InstructorCourse Department Student * 1..* 1 has member * * attends * 1..* teaches 1..* 0..1 1chairperson assigned to Considering a bunch of classes and their association relationships

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Lawrence ChungCS6359.0T1: Module 419 Modeling Structural Relationships Composite is a stronger form of aggregation. Composite parts live and die with the whole. Liver Body Heart Wheel Car Engine Composite Aggregation

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Lawrence ChungCS6359.0T1: Module 420 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..

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Lawrence ChungCS6359.0T1: Module 421 Hints & Tips Modeling relationships Use dependencies when relationship is not structural. Use generalization with is-a relationship. Dont 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.

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Lawrence ChungCS6359.0T1: Module 422 Summary Relationships Dependency Generalization Association -Links and Link Attributes -Aggregation Modeling techniques Simple dependencies Single inheritance Structural relationships

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Lawrence ChungCS6359.0T1: Module 423 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?