Object Modeling (2) Chapter 3 (2) Part 1: Modeling Concepts Object-Oriented Modeling and Design Byung-Hyun Ha

Lecture Outline  Introduction  Links and associations  Advanced link and association concepts  Generalization and inheritance  Remaining parts

Introduction  Class and objects  A class is abstraction or specification of a group of similar objects  e.g. Person vs. Joe, Mary, …  e.g. Every instance of our Vector has x, y, and length(). Person (Person) Joe Smith 24 (Person) Mary Sharp 52 name: string age: integer public class Vector { double x; double y; double length() { double len = Math.sqrt(x * x + y * y); return len; }

Introduction  Association vs. links  An association is abstraction or specification of a group of similar links  e.g. Has-capital Country name City name Has-capital (Country) Canada (City) Ottawa Has-capital (Country) France (City) Paris Has-capital (Country) Senegal (City) Dakar Has-capital

Introduction  Association vs. links (cont’)  e.g. Intersects Line name Point name Intersects 2+

Links and Associations (cont’)  Multiplicity specification  How many instances of one class may related to a single instance of an associated class  One or many  Optional  Numbers PlayboyGirl loves RomanticistGirl loves BoyGirl loves 1+3-5

Links and Associations  Multiplicity depends on problem  e.g. tax collection application  e.g. auto workers’ union  It exposes hidden assumption built into the model PersonCompany Works-for PersonCompany Works-for

Advanced Link and Association Concepts  Role  One end of association  Role name  A name that uniquely identifies one end of an association PersonCompany Works-for employeeemployer UserDirectory container contents owner authorized user

Advanced Link and Association Concepts  Role name  All role names on the far end of associations attached to a class must be unique  The role name is a derived attribute of the source class  Role name for n-ary association  Association of degree 3 or more cannot simply be traversed from one end to another as binary associations can ProjectLanguage Person

Advanced Link and Association Concepts  Link attributes  Properties of a link in an association FileUser Accessible by access permission /etc/termcap(read)John Doe /etc/termcap(read-write)Mary Brown /usr/doe/.login(read-write)John Doe

Advanced Link and Association Concepts  Link attributes for one-to-many association  e.g. works-for and manages Person name social security no. address Company name address Works-for salary job title Manages worker boss performance rating

Advanced Link and Association Concepts  Folding link attributes  It is possible to fold link attributes for one-to-one and one-to- many associations into the class opposite the “one” site  How is it possible and which one is preferred? Person name social security no. address Company name address Works-for salary job title Person name social security no. address salary job title Company name address Works-for

Advanced Link and Association Concepts  Link attributes for ternary association PitcherYear Team wins losses WL Harry EisenstatCleveland Indians Harry EisenstatDetroit Tigers Willis HudlinCleveland Indians Willis HudlinCleveland Indians Willis HudlinWashington Senators Willis HudlinSt. Louis Browns194001

Advanced Link and Association Concepts  Modeling an associations as a class  Each link becomes one instance of the class  It is useful when links can participate in associations with other objects or when links are subject to operations UserWorkstation Authorized on Authorization priority privileges start session Director home directory

Advanced Link and Association Concepts  Ordering  A special kind of constraint WindowScreen Visible-on {ordered}

Advanced Link and Association Concepts  Qualification  A qualified association relates two object classes and a qualifier  The qualifier distinguishes among the set of objects at the many end of an association DirectoryFile DirectoryFile file name

Advanced Link and Association Concepts  Examples  Ticker symbol of company in stock exchange  Company and office Stock exchange Company ticker symbol lists Stock exchange Company ticker symbol lists CompanyPerson office officerorganization

Advanced Link and Association Concepts  Aggregation  “Part-whole” or “a-part-of” relationship  Used for components and assembly Existence of a part depends on existence of whole  Tightly coupled form of association extra semantics Transitivity If A is part of B and B is part of C, then A is part of C Antisymmetric If A is part of B, then B is not part of A Propagation of properties e.g. location of a door handle is obtained from the door; door obtains its properties from the car, … DocumentParagraphSentence

Generalization and Inheritance  Generalization  The relationship between a class and one or more refined version of it superclass and subclass  “is-a” relationship  Transitive ancestor and descendant An instance of a subclass is simultaneously an instance of all its ancestor classes Equipment name manufacturer weight cost PumpTank flow ratevolume …

Generalization and Inheritance  Examples  Fig and 3.24  Some guidelines  Do not nest subclasses too deeply  “An inheritance hierarchy that is two or three levels deep is certainly acceptable; ten levels deep is probably excessive; five or six levels may or may not proper”  Inheritance, generalization, and specialization  Different viewpoints of the same relationship  A subclass is a special case of its superclass  Don’t borrow a class using inheritance, when the new class is not really a special case of the original class!

Remaining Parts  Grouping constructs  Module and sheet  A sample object model  Fig. 3.25: object model for window system  Practical tips  …

Homework  HW7  Exercise 3.6 (p. 50)  HW8: extend E3.6 a.Modify the class diagram in Figure E3.6 (p. 51) so as to handle unary minus and functions (e.g., sqrt(x) for calculating square root of x) with arbitrary number of arguments. b.Prepare an instance diagram for the class diagram you made for the expression -(B + sqrt(B*B – 4*A*C))/(4*A*A).