1. Information system analysis and design
Dr. Dina Tbaishat

2. Recap
Last two lectures we looked at DFDs as a graphical tool to look at what happens in a system
Today we shall look at data dictionaries and other tools used to analyse structured decisions ; these are: decision tables, decision trees and structured English)

3. Data Dictionaries Can be called meta data repository
Data dictionary provides a descriptive list of names, definitions, and attributes of data elements to be captured in an information system
This indeed helps programmers understand the system
Data dictionary is built for certain context, it associates context with elements of the structure
Used to develop and maintain a database

4. Data dictionary benefits:
Improved data quality
Improved documentation and control
Reduced data redundancy
Reuse of data
Consistency in data use
Easier data analysis
Improved decision making based on better data
Simpler programming

5. Field name
Data type
Other information
Customer ID
Auto-number
Primary key
Name
Text
Size: 15
Number
Size: 10

6. Decision Tables
Decision tables are used to model complicated programming logic. They can make it easy to see that all possible combinations of conditions have been considered; when conditions are missed, it is easy to see this.
In the top left corner the conditions are listed, they can be in the form of a question with a Yes or No answer or simply, given some alternative (ex: Male and Female)
In the bottom left part actions are listed
The combinations of responses are called rules (the columns)

7. If there are n conditions, there are 2n rules (columns), ex: 2 conditions  22 =2 x 2 = 4 rules)

8. Condition one Y N
Condition two
Action 1 X
Action 2
Action 3

10. Powerful presentation
Less errors
Decision tables are appropriate when the number of actions is large – they handle complexity better
Group related rules into single table and combine tables to achieve decisions
However, they have less graphical structure and not very easy to construct (compared to decision trees)
No indication is given about the sequence of actions

11. Decision Trees
A diagram that is read from left to right. The leftmost node in a decision tree is called the root node
The branches from a decision node to the right represent the set of decision alternatives that are available
One, and only one, of these alternatives can be selected
The small circles in the tree are called chance nodes

12. The number shown in parentheses on each branch of a chance node is the probability that the outcome shown on that branch will occur at the chance node
The right end of each path through the tree is called an endpoint

14. Structured English
Using English language with the syntax of programming, to represent the logic of the system
It can be kept in automated format
For beginners, it might take time to build
It also seems to be more formal than it is
An example is shown next:

15. Process Validate Customer Enter customer number Seek customer number in Customer file if customer number found then    create order record in Order file    go to process 1.2 else    display error message    ask user if he/she wants to create new customer record in Customer file    if yes then       go to process 1.3    else       terminate order entry process    endif endif