7-1 © Prentice Hall, 2007 Week 5: Conceptual Data Modeling Object-Oriented Systems Analysis and...

7-1© Prentice Hall, 2007

Week 5:Week 5:Conceptual Data ModelingConceptual Data Modeling

Object-Oriented Systems Analysis and Design

Joey F. George, Dinesh Batra,

Joseph S. Valacich, Jeffrey A. Hoffer

Week 5 7-2© Prentice Hall, 2007

Chapter ObjectivesChapter Objectives

After studying this chapter you should be able to:– Determine how to develop conceptual

data models from use cases.– Understand UML notations for

conceptual data modeling.– Explain relationship characteristics such

as degree and multiplicity.


Chapter Objectives Chapter Objectives (Continued)(Continued)

After studying this chapter you should be able to:– Describe data relationships such as

association, aggregation, and generalization.

– Describe different kinds of attributes such as identifier, multivalued, and derived.


What Is a Conceptual Data What Is a Conceptual Data Model?Model?

A detailed model that shows the overall structure of organizational data; it is independent of any database management system or other implementation considerations.

Represented by UML class diagrams


Use cases are key inputs to conceptual data modeling.


Conceptual model sets the stage for more detailed model, and ultimately system design


Conceptual Data Model ElementsConceptual Data Model ElementsClassesAttributesIdentifiersAssociations, aggregations, compositionsGeneralizationsTime dimensionsIntegrity rulesSecurity controls


What Is an Object?What Is an Object?

An entity that encapsulates data and behavior

Examples: product, employee, order, line item

Class – a set of objects that share the same attributes, operations, relationships, and semantics (abstract)

Instance – a single object (concrete)


Class

Instances


UML Class symbol has three parts:

1) Name2) List of attributes3) List of operations


What is an Attribute?What is an Attribute?

A named property of a class that describes a range of values that instances of the attribute may hold


Types of AttributesTypes of AttributesSimple attributes – contain single data item

Identifiers – connect unique key value

Multivalued attributes – contain multiple values simultaneously

Composite attributes – group of related attributes


Stereotypes in Class DiagramsStereotypes in Class Diagrams

Stereotype – a construct that extends the UML vocabulary

Identifier stereotype <<PK>> for primary key

Multivalued stereotype <<multivalued>>


Primary key is a unique identifier; no two Student instances will have the same studentId value.


Identifiers and KeysIdentifiers and Keys

Identifier – an attribute or combination of attributes that is selected as the unique characteristic for a class

Candidate key – an attribute or combination of attributes that uniquely identifies each object of a class

Primary key – a candidate key that is selected as the unique identifier of the class


Multivalued attribute can contain multiple values; a student may have several phone numbers


Composite attributes have multiple sections (subattributes).They are treated as separate classes in conceptual data models.


What Is a Relationship?What Is a Relationship?

A semantic connection between objects of one or more classes

In UML, represented as a line connecting two or more class boxes (or connecting one class to itself)


What Is Relationship Degree?What Is Relationship Degree?The number of classes that participate in a

relationship

Main degrees:– Unary – a relationship between objects of the

same class– Binary – a relationship between objects of two

different classes– Ternary – a relationship between objects of

three different classes


This is a binary relationship, which indicates that an employee works in a department.


Roles identify the purpose of each class in the relationship.


Unary relationships exist between instances of the same class


Note: a ternary relationship is not the same as three binary relationships. It is a relationship that links three separate classes simultaneously.


What Is Relationship Multiplicity?What Is Relationship Multiplicity?

The range of the number of objects in Class A that can or must be associated with each object of Class B.

A multiplicity is made up of:– A minimum cardinality – the minimum number

of Class A objects possible– A maximum cardinality – the maximum

number of Class A objects possible


Relationship MultiplyRelationship Multiply

Relationships can be:

– One – to – one

– One – to – many

– Many – to – many


Multiplicity notation is: min..max

This shows that one movie can be stocked as any number of videotapes, or none at all


Fixed cardinality involves an actual number instead of the generic n

This indicates that the maximum number of sections an instructor can teach is 6


Roles make it clearer to see which should be on the one side and which should be on the many side of the relationship.


What Is an Associative Class?What Is an Associative Class?

A many-to-many association that the data modeler chooses to model as a class

Particularly useful if the association contains attributes of its own

Represented as a class connected to an association with a dotted line


A Certificate represents a relationship between an employee and a course, and has an attribute pertaining to that relationship


Sometimes associative classes have their own relationships with other classes.


Types of AssociationsTypes of Associations• Association – no object is subordinate to any other.

• Aggregation – one class represents the whole, and the other represents the part, but it is a loose coupling.

• Composition – an aggregation with a tight coupling. The whole and the part cannot exist without each other.


Closed diamond indicates composition(course line item cannot exist without course registration)

Open diamond indicates aggregation(A player is part of a team, but could also exist without being part of a team)


What Is a Composite Structure What Is a Composite Structure Diagram?Diagram?

A diagram that shows how a whole is made up of its parts, especially in cases where the whole has a large number of interating parts

Useful to reduce clutter in diagrams with many associations

Introduced in UML 2


What Is Generalization?What Is Generalization?

A superclass – subclass relationship in which one class forms a broader category in which the other class is a sub-category

Inheritance – A subclass will inherit all the attributes and operations of its superclass; an instance of the subclass contains all the same information (plus more) as an instance of the superclass.

Inheritance is an “is-a” relationship


Multiple inheritance is complicated and not supported by all object-oriented programming languages.


RecapRecap

After studying this chapter we learned to:– Develop data models from use cases.– Use UML notation for conceptual modeling.– Understand relationship multiplicity and

degree.– Work with aggregation, composition, and

generalization.– Work with identifier, multivalued, and derived

attributes.

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