Systems Analysis Course

• Home
• 1.What is a System
  • Introduction
  • Parts of a System
• 2.System Lifecycle
  • Project Management
  • Project Lifecycle
  • Check Understanding
  • SDLC Comparison
  • Exercise
• 3.Feasibility Study
  • Sections
  • Exercise
• 4.CostBenefit Analysis
• 5.System Investigation
  • Introduction
  • Methods
  • Identify method
  • Exercise
• 6.Data Flow Diagrams
  • Introduction
  • Video
  • Definitions
  • Steps to create
  • Exercises
• 7.Relational Diagrams
  • Terminology
  • Examples
  • Exercise
  • Using a DFD level1
• 8.Data Dictionary
• 9.Design Specification
• 10.Creating a Test Plan

 

 

Lesson 8 - Data Dictionary - ERD Attributes

Remember an Entity is a real-world thing (customer, products, books) that need to represented in a system. Entities have attributes which are elements that define a particular entity.

The top or first level ERD identifies the entities and their relationships, it is a useful tool in describing the application domain and is used as a base document to determine further detail.

The next step is to identify the attributes of those entities, this may be done in conjunction with the User Requirement Specification (URS), if one exists, and/or by structured interviews with the project sponsors and users.

Several methods exist for showing attributes on an ERD - we will use a table form (similar to Access) relationships view.

One or more of the attributes of an entity is defined as the PRIMARY KEY. To guarantee uniqueness numbers are normally used for primary key attributes. Therefore in the example above the primary key for the STUDENT entity would be IDNumber.

 

---

 

Exercise 9 - Using the ERD below for the Rapid Results system, work out the attibutes required on each entity.

---

 

How do we know that a lesson is for a pupil? One of the attributes of the entity 'Pupil' will be the 'Pupil number'. This unique number identifies the 'Pupil' and is the primary key of the entity. When a lesson is booked for that pupil an occurrence of the 'lesson' entity is created. So that it is possible to tell which Pupil is having the lesson the 'Pupil number' is inserted into the occurrence of the 'lesson' entity. This is known as a FOREIGN Key.

When the attributes have been identified the information about each Entity and its attibutes need to be documented in a DATA DICTIONARY. You create a table for each entity and then list each attribute. Each attribute must have a unique name. The relationship, desciption and purpose of each attribute must be explained. If the attribute is a Primary or Foreign key this should be identified in Key Type. You need to work out the length of data required in each field and also the format of the data.

 

---

 

Exercise 10 - Using the attributes you identified in exercise 9 create a Data Dictionary for the Rapid Results ERD.

 

Copyright JK Nichols 2009