2-2-2 Object-Oriented Design

• • “is-a” relationship (specialization/generalization relationship)
  This is a relationship in which sections common to several classes are extracted to define a higher-level class. The higher-level class is called a superclass and the lower-level classes are called subclasses. Extracting the common sections from multiple subclasses is called generalization; conversely, refining a superclass is called specialization.

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Automobile is above Passenger automobile, Bus and Truck. Passenger automobile is above Sedan and Station wagon. A downward arrow on the left is Specialization; an upward arrow on the right is Generalization.

• • “part-of” relationship (aggregation/decomposition relationship)
  This is a relationship in which multiple lower-level classes are aggregated to compose a single higher-level class. The development of higher-level classes into lower-level classes is called decomposition, and the grouping of lower-level classes into higher-level classes is called aggregation.

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Automobile is above Chassis, Engine and Tire. Chassis is above Seat and Door. The left downward arrow is Decomposition and the right upward arrow is Aggregation.

• • “has-a” relationship
  This relationship means that a higher-level class holds a lower-level class. This relationship has almost the same meaning as the “part-of” relationship. However, they differ in that whereas the higher-level class is not possible in the “part-of” relationship

if even one lower-level class is missing, it is possible in the “has-a” relationship even if multiple lower-level classes are missing.

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Automobile has Child seat, Drink holder and Car navigation system below it.

• • Inheritance
  Attributes defined in an upper-level class can be passed (or inherited) to lower-level classes. Inheritance includes single inheritance from one superclass, and multiple inheritance from multiple superclasses. Inheritance does not exist in “part-of” relationships. The rewriting, by an inheriting lower-level class, of methods that are defined in a superclass is called override (redefinition). · 2 questions

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The Automobile class contains Model and engine displacement and has Bus (Capacity) and Truck (Load capacity) beneath it. A rightward arrow labelled Inheritance leads to Truck containing Model, engine displacement and load capacity.

• • Differential programming
  This is a programming technique in which a superclass is inherited, and only the portions differing from the superclass are defined in the subclasses.
• • Polymorphism
  This is the ability of actions (or behaviors) for a given message to differ according to the class (i.e., object). Polymorphism is implemented by override (redefinition) etc. · 2 questions

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Superclass Bank deposit (Interest calculation) receives Same Message. Its subclasses are Term deposits, calculated as compound interest, and Ordinary deposit, calculated as simple interest. The lower label is Action differs.

• • Delegation
  This is the ability to delegate processing to other classes (i.e., objects). · 1 question

• • Propagation
  This is the ability, when operations are applied to a given class (i.e., object), to automatically apply the operations to other related classes (i.e., objects).
• • Role
  It is possible to group multiple instances and define roles. Actions will change when roles differ, even for instances of the same class.

[Development phases in the object-orientated development model]

Object-oriented analysis	Object-oriented design		Object-oriented programming
	Architectural design	Class design

View original table · p. 289

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(i) OOA (Object-Oriented Analysis) This models the real world that is the target of development through object orientation (i.e., the integration of data and procedures). E-R diagrams and state transition diagrams are used in the modeling.

• • E-R diagram / ER model
  These are data models that represents the targeted work as entities and relationships among entities. They are used in data modeling, and others which represents the data structures used in work.

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Wholesaler connects by a right-pointing arrow to Product. Product connects to Customer with a line that has arrowheads at both ends.

• • One fact in one place
  This is a concept in data analysis that manages one fact (i.e., information) in one place. It checks whether the same data, used in multiple tasks, is managed

under different names. In a database, one fact in one place is achieved by performing normalization. (ii) OOD (Object-Oriented Design) The architectural design (i.e., global design) that equates to external design in the waterfall model and the class design (i.e., local design) that equates to internal design are carried out. (iii) OOP (Object Oriented Programming) Object orientation is more the concept of clearly defining methods of using classes than the concept of creating programs. In this phase, class libraries (i.e., libraries for preserving created classes) and packages are referenced in order to reuse existing classes. Programming languages used include Java and C++.

• • CORBA (COmmon Request Broker Architecture)
  This is a standard specification that enables message exchange among objects developed by using different programming languages in a distributed environment.
• • IDL (Interface Definition Language)
  This is a set of rules concerning interfaces for reusing created objects from other programming languages.

[Other languages]

• • ADL (Architecture Description Language)
  This is a language that describes the architecture (i.e., structure) of systems (i.e., software). UML can be considered a type of ADL.
• • DDL (Data Definition Language)
  This is a language that defines the logical structure and names of databases.