MIS 210 Fall 2004

Lecture 4:Data Modeling

Process Modeling

MIS 210Information Systems I

MIS 210 Fall 2004

Data Models

MIS 210 Fall 2004 Sylnovie Merchant, Ph. D.

Entity-Relationship Diagrams

• Data-oriented approach– uses the data and the relationships among data

to model requirements– purpose is to show the data used in the system– good for modeling data stores from a DFD

• A representation of organizational data.– Shows the rules about the meanings and

interrelationships among the data.

MIS 210 Fall 2004

E-R Diagrams

• Defined– A graphical representation of an E-R model.– E-R model

• a detailed, logical representation of the entities, associations, and data elements for an organization or business area.

MIS 210 Fall 2004

E-R Symbols

Entity

Attribute

Relationship

MIS 210 Fall 2004

Terminology• Entity

– a “thing” in the real world– has an independent existence

• Attribute(s)– One specific piece of information about a thing– a property of the entity – has a value (or value set or domain)

• Cardinality– the number of instances of an entity that are associated with

another entity– a single occurrence of an entity

MIS 210 Fall 2004

Data Entities

An Entity is a thing the users need to know (i.e, record) something about.

MIS 210 Fall 2004

Types of Things

MIS 210 Fall 2004

Types of Attributes

• Identifier (primary key / key attribute)– An attribute (or attributes) selected as the unique,

identifying characteristic for an entity.

• Foreign Key– An attribute (or attributes) in one database table

that is the primary key in another database table

MIS 210 Fall 2004

Attributes and Their Values

All videos/DVDs have the following attributes:

Product ID numberProduct NameProduct DescriptionCategory IDSupplier IDSerial Number

Each video/DVD has a value for each attribute:

1WoodstockConcertOtherWRNRBRDVD19925C1

MIS 210 Fall 2004

Relationships• Relationship

– Naturally occurring association among specific things

– Occur in two directions– Cardinality/multiplicity

MIS 210 Fall 2004

Relationships

• Degree of Relationship– number of entities that participate in that relationship

• Unary (recursive)– degree one– A relationship between instances of one entity.

• Binary – degree two– A relationship between instances of two entities

• Ternary– A relationship between instances of three entities

MIS 210 Fall 2004

Cardinality of Relationships

MIS 210 Fall 2004

Relationships and Cardinality

MIS 210 Fall 2004

Trucking….One Approach

Truck

carries

Shipment Warehouses

delivers to

stored at

Retail Stores

1

m

m

1

m

m

*Truck IDVolume Weight

*Shipment NumberShipment VolumeWeightDestination

Tripsmakes1 m

MIS 210 Fall 2004

Trucking….Another Approach

Truck

carries

Shipment Warehouses

delivers to

stored at

Retail Stores

1

m

m

1

m

m

Truck IDVolume Weight

Shipment NumberShipment VolumeWeightDestination

Tripsmakes1 m

MIS 210 Fall 2004

Data Dictionary

MIS 210 Fall 2004

Data Dictionary Defined

“…the data dictionary collects and coordinates specific data terms, and it confirms what each term means to different people in the organization.”

Kendall & Kendall

MIS 210 Fall 2004 Sylnovie Merchant, Ph. D.

Data Dictionary(aka, Project Repository)

• Repository for all primitive-level data structures and data elements within a system.

• Use information from DFDs or ERDs to create the DD

• DD details each of the data items, data flows, processes, etc. in a system

• For example: DD entry for data items would show characteristics such as size, type, description, ranges, etc.

MIS 210 Fall 2004

Process Models

MIS 210 Fall 2004

Process Modeling

• Focus on the internal structure and processes in the DFD

• Most popular models– Structured English– Decision Tables– Decision Trees

MIS 210 Fall 2004

Structured English

• Form of English used to specify the processes in a DFD

• Makes use of nouns and action verbs

• Similar to pseudocode

MIS 210 Fall 2004

Structured English ExampleEnd of Month Processing

DO FOR EACH INVENTORY ITEMCOUNT STOCK IN STOCK ROOM

ENTER COUNT ON INVENTORY SHEET

END DO

MIS 210 Fall 2004

Decision Tables • Lays out the logic of complex problems where

there are multiple actions based on multiple decisions.

• Four components– conditions– decision rules– actions– action entries

MIS 210 Fall 2004

Decision Tables

• The total possible number of decision rules represents the total possible combinations, or permutations, of the condition values

• For example, for yes or no values:number of decision rules = 2n

• For three conditions with yes or no valuesnumber of decision rules = 2n = 23 = 8

MIS 210 Fall 2004

Decision Tables

• For a range of values– example, age: 1=18 to 20, 2=21-30, 3=31-40, 4=41-50,

5=50 or over

– five (5) values for this condition

• What if there are a combination of different values– yes or no values

– five values

– total possible values = 2 x 5=10

MIS 210 Fall 2004

Decision Trees

• A graphical representation of a decision structure.

• Difficult to use for a complex situation.