File and Database Design;
Logic Modeling
Class 24
SDLC
Project Identification
& Selection
Project Initiation
& Planning
Analysis
Logical Design
Physical Design
***
Implementation
Maintenance
Databases
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File Systems
Databases
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Hierarchical Database Model
Network Database Model
Relational Database Model
Object Oriented Database Model
File Systems
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Each new application is designed with
its own set of files.
Problems:
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Changes in files require changes to
programs.
Uncontrolled redundancy
Inconsistent data
Limited data sharing
Database Approach
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Negatives
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Need new, specialized
personnel
Need for explicit
backups
Interference due to
shared data
Organizational conflict
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Postives
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Minimal data redundancy
Consistent data
Integration of data
Sharing of data
Data independence
Ease of application
development
Reduced program
maintenance
Designing a relational
database
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Create a table (file) for each entity type.
Choose a primary key for each table.
Choose appropriate data types and value
restrictions for each field.
Create new tables to represent many-to-many
relationships.
Add foreign keys to represent one-to-many
relationships.
Define referential integrity constraints.
Evaluate schema quality and make necessary
improvements.
What we’re looking at
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Databases, Tables (files, entities),
Records, Fields (attributes)
How we’ll define above in the Data
Dictionary
Tables
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Each entity on your ER diagram will
become a table in your database.
Records
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A row in the table.
A group of fields (or attributes) stored
in adjacent memory locations and
retrieved together as a unit.
Fields
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May also be called an attribute or data
element.
All fields (or attributes on your ER
diagram) will be defined in the Data
Dictionary.
Fields
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Name
Data type
Primary key(s)
Data integrity
Handling missing data
Ownership
Data Integrity
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Default value
Picture control
Range controls
Null Value controls
Data Dictionary
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The repository of all data definitions for
all organizational applications.
What we’ll show in a DD:
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Table (file) (entity) name
All fields (attributes) within the table.
For each field:
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Name
Note if primary key
Definition/description of field
Data type (page 352, or whether its
numeric or character plus the length)
TABLE: PIG
Primary
Key
*
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
Logic Modeling
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Knowing what’s going on inside the
programs. What is the logic to create
the reports, calculated fields?
We’ll show logic modeling through use
of decision trees and decision tables.
Decision Tables
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A matrix representation of the logic of a
decision, which specifies the possible
conditions for the decision and the
resulting actions.
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Condition stubs
Action stubs
Rules
Steps in creating Decision
tables:
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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”.
Examples!
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Decision Trees
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A graphical representation of a decision
situation in which decision situation
points (nodes) are connected together
by arcs (one for each alternative on a
decision) and terminate in ovals (the
action that is the result of all of the
decisions made on the path leading to
the oval
Decision trees
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Often used for statistical reasons – for
calculating probabilities and making
choices based on probabilities.
Used more often for “simpler”
problems.
Examples!
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