Class24_DesigningDatabases_LogicModeling

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File and Database Design;Logic Modeling

Class 24

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SDLCProject Identification

& Selection

Project Initiation

& Planning

Analysis

Logical Design

Physical Design***

Implementation

Maintenance

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Databases File Systems

Databases

Hierarchical Database Model

Network Database Model

Relational Database Model

Object Oriented Database Model

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File Systems Each new application is designed with

its own set of files.

Problems: Changes in files require changes to

programs.

Uncontrolled redundancy

Inconsistent data

Limited data sharing

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Database Approach Negatives

Need new, specialized

personnel Need for explicit

backups

Interference due to

shared data Organizational conflict

Postives

Minimal data redundancy

Consistent data Integration of data

Sharing of data

Data independence

Ease of applicationdevelopment

Reduced programmaintenance

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Designing a relational

database Create a table (file) for each entity type.

Choose a primary key for each table.

Choose appropriate data types and valuerestrictions for each field.

Create new tables to represent many-to-many relationships.

Add foreign keys to represent one-to-manyrelationships.

Define referential integrity constraints.

Evaluate schema quality and make necessaryimprovements.

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What were looking at Databases, Tables (files, entities),

Records, Fields (attributes)

How well define above in the DataDictionary

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Tables Each entity on your ER diagram will

become a table in your database.

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RecordsA row in the table.

A group of fields (or attributes) storedin adjacent memory locations andretrieved together as a unit.

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Fields May also be called an attribute or data

element.

All fields (or attributes on your ERdiagram) will be defined in the Data

Dictionary.

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Fields Name

Data type

Primary key(s)

Data integrity

Handling missing data Ownership

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Data Integrity Default value

Picture control

Range controls

Null Value controls

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Data Dictionary The repository of all data definitions for

all organizational applications.

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What well show in a DD: Table (file) (entity) name

All fields (attributes) within the table.

For each field: Name

Note if primary key

Definition/description of field Data type (page 352, or whether its

numeric or character plus the length)

TABLE PIG

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TABLE: PIG

PrimaryKey

Attribute

Name

Attribute Definition Attribute Type

* PigID The unique identifier

of the pig

5 numeric characters

PigName The name of the pig 15 alpha characters

PigWeight The weight, in pounds

and ounces of the pig

6 numeric characters, with 2

numbers after the decimal

PigGender The gender of the pig

either male or female

1 alpha character, M or F

are allowed

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Logic Modeling Knowing whats going on inside the

programs. What is the logic to create

the reports, calculated fields?

Well show logic modeling through use

of decision trees and decision tables.

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Decision TablesA matrix representation of the logic of a

decision, which specifies the possible

conditions for the decision and theresulting actions.

Condition stubs

Action stubs Rules

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Steps in creating Decision

tables: Name all conditions and the values each

condition can assume.

Name all possible actions that can occur. List all possible rules based on every possible

combination of conditions.

Define the actions for each rule. Simplify the decision table by removing

indifferent conditions.

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Examples!

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Decision TreesA graphical representation of a decision

situation in which decision situation

points (nodes) are connected togetherby arcs (one for each alternative on adecision) and terminate in ovals (the

action that is the result of all of thedecisions made on the path leading tothe oval

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Decision trees Often used for statistical reasons for

calculating probabilities and making

choices based on probabilities. Used more often for simpler

problems.

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Examples!