LESSON05Jerry Kotuba

Object Oriented Methodologies 1

Agenda

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Solution I-C-E-03 & 04 Posted Take up the Class Diagrams

Class Diagrams Whole-to-part associations I-C-E-05

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SYST39409 - Object Oriented Methodologies

Generalization, Inheritance & Constraints

generalization path solid line with hollow

arrowhead pointing from subclass to superclass

indicate basis of generalization

name the path for the attribute being removed = called the discriminator

discriminator shows which property is abstracted by a generalization relationship

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SYST39409 - Object Oriented Methodologies

Constraints on Generalization

constraints on the subclasses

overlapping: descendent may be descended from more than one of the subclasses student can be both a

research and teaching assistant

disjoint: descendent may not be descended from more than one of the subclasses patient can not be both

out and residentJerry Kotuba

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SYST39409 - Object Oriented Methodologies

Constraints on Generalization

complete: all subclasses are listed only have out and

resident patients incomplete: all

subclasses are not listed more subclasses are

available can have casual, part-

time employees

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Whole-to-Part Associations

The UML provides ways to model two types of whole-to-part associations – aggregation and composition.

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Definitions

aggregate: In an aggregation, the class representing the whole.

aggregation: An association between classes representing a part-to-whole relationship in which the parts and the whole may exist independently and in which a single part may be associated with more than one whole at the same time.

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Definitions…cont’d

composite: In a composition, a class representing the whole.

composition: An association between classes representing a whole-to-part relationship in which the parts may belong to only one whole at a time and the whole does not exist without its parts.

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Example of an Aggregation

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Example of a Composition

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Aggregation and Composition

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Categories of Whole-to-Part Associations

There are three relationships that sometimes occur in an object model: Assemblies of parts Members of groups Containers and their contents

You may find these useful for making your model a better tool for understanding and communication.

The model can always be built without these. They do not really affect its use for system design, just for talking to the users.

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Assemblies of parts

Taking something apart into its components is a technique we humans often use to understand how something works.

Often we find it improves our understanding to model A product and its components A business consists of branches,

departments, etc. A country consists of states, provinces,

counties, boroughs, shires, towns, villages, cities, etc.

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Containers and their contents Container-Contents is a different and less

common relationship. In some situations we may find it helpful to

view a relationship as one of these, e.g., Truck or Aircraft and the Products or Shipments that

it carries An actual shipping container and the goods it holds A ship, bus or airplane and its passengers A building and the businesses it houses.

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Assemblies of parts Vs Containers and their contents

The essential difference between these relationships is that: With Assemblies of

parts, if you take the component away, the assembly (whole) probably won’t work any more Take a wheel off a

car Take a hand off a

clock Take a leg off a table.

A Container, however, is still a perfectly good Container, even without its Contents The jar is still OK even

without the “hunny.” And the Contents are

perfectly OK without the Container (although the “hunny”

might get all over one’s paws!)

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Collection-Member (members of groups)

Collection-Member is also a different and relatively uncommon relationship.

Sometimes we meet an actual collection: A library full of books An art gallery A stamp or jewelry

collection A fleet of trucks, ships or

aircraft

Other times it may help to use this to describe: A church, club or

regiment and its members

An inventory of furniture or equipment

A herd, mob, flock, school or skein of animals.

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Your Turn…

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Think about a book, which consists of a cover, table of contents, chapters and an index. Chapters in turn have pages, paragraphs and words. Show the special case of association between classes described here including the multiplicity.

Next class…

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Wrap-up Class Diagrams Test Review Return Assignment No 1 Quiz No 2

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Your turn…ICE-05

SLATE2

Jerry Kotuba