Ch 5: Data Modeling

Structure Models

• Describes the data and information structures inherent in a business process(es).

• Create a blueprint for the development of a relational database to support the collection,

• aggregation, and communication of process information

• Tools for documenting, implementing databases, planning, and discussing.

Data Models:

• Graphic representations of the conceptual contents of databases; data models support communication about database contents between users and designers of the database.

Model of logical database structures must be able to describe:

1. The entities or things in the domain of interest

2. The relationship among those things

3. The cardinalities that describe how many instances of one entity can be related to another

4. The attitudes or characteristics of the entities and relationships

Unified Modeling Language Class Diagrams

• Object Management Group maintains and publishes the specification for the UML

  • Consortium of computer industry members

Class Diagrams:

• one type of diagram within UML that describe the logical structure of a database system. 

Classes

• Separately identifiable collection of things (objects) about which the organization wants to collect and store information represented by a rectangle with three compartments.

• Typically implemented as tables in a relational database where individual instances of objects are represented as rows 

Associations

• Depicts relationship between two classes with verbs or verb phrases

  • ex.) customers (class) participate in sales (class)

  • ex.) professors (class) teach courses (class)

• When the business purpose of the association is not clear, the association can be named by placing the text name on the line.

Multiplicities

• Describe the minimum and maximum number of times instances in one class can be associated with instances in another class represented by pair of numbers placed on opposite side of the association

• Maximum values describe the nature of the relationship between classes

Attributes

• Data elements (columns) that describe the instances (rows) in a class.

• The full specification of attributes would include data type, default value, constraints, and other descriptive information

Primary Key:

• An attribute or a combination of attributes that uniquely identifies an instance of a class in a data model or a specific row in a table. ex.) student ID

Foreign Keys:

• Attribute that allows database tables to be linked together; foreign keys are the primary keys of other tables placed in the current table to support the link between the two tables.