Data Dictionary

A data dictionary is a structured repository of data elements in the system. It stores the descriptions of all DFD data elements, that is, details and definitions of data flows, data stores, data stored in data stores, and the processes.

A data dictionary improves the communication between the analyst and the user. It plays an important role in building a database. Most DBMSs have a data dictionary as a standard feature. For example, refer the following table −

Decision Trees

Decision trees are a method for defining complex relationships by describing decisions and avoiding the problems in communication. A decision tree is a diagram that shows alternative actions and conditions within a horizontal tree framework. Thus, it depicts which conditions to consider first, second, and so on.

Decision trees depict the relationship of each condition and their permissible actions. A square node indicates an action and a circle indicates a condition. It forces analysts to consider the sequence of decisions and identifies the actual decision that must be made.

The major limitation of a decision tree is that it lacks information in its format to describe what other combinations of conditions you can take for testing. It is a single representation of the relationships between conditions and actions.

For example, refer the following decision tree −

Decision Tables

Decision tables are a method of describing the complex logical relationship in a precise manner which is easily understandable.

• It is useful in situations where the resulting actions depend on the occurrence of one or several combinations of independent conditions.
• It is a matrix containing rows or columns for defining a problem and the actions.

Components of a Decision Table

• Condition Stub − It is in the upper left quadrant which lists all the conditions to be checked.
• Action Stub − It is in the lower left quadrant which outlines all the action to be carried out to meet such conditions.
• Condition Entry − It is in the upper right quadrant which provides answers to questions asked in the condition stub quadrant.
• Action Entry − It is in the lower right quadrant which indicates the appropriate action resulting from the answers to the conditions in the condition entry quadrant.

The entries in the decision table are given by Decision Rules which define the relationships between combinations of conditions and courses of action. In rules section,

• Y shows the existence of a condition.
• N represents the condition, which is not satisfied.
• A blank – against action states it is to be ignored.
• X (or a check mark will do) against action states it is to be carried out.

For example, refer the following table −