After numerous interviews, prototypes, data flow diagrams, data dictionary entries, and UML diagrams have been completed, Anna and Chip both start work on the entity-relationship model. “I’ll be responsible for creating the Microsoft Access table relationships,” Anna promises. Chip volunteers to complete an entity-relationship diagram. “Let’s compare the two diagrams for accuracy and consistency when we’re done,” Anna suggests, and so they do.

Figure shows the entity-relationship diagram for the computer inventory system. Visible Analyst calls each of the rectangles an entity. Each entity represents a database table of information stored in the system, corresponding to a data store on the data flow diagram or an entity class on a sequence or class diagram. Each of the diamond rectangles represents an associative entity representing a relationship between the data entities. A rectangle with an oval in it represents an associative entity that cannot exist without the connecting entity. These are usually repeating elements. Microsoft Visio uses rectangles to represent both an associative and an attributive entity.

1. Use Microsoft Visio or Visible Analyst to view the un normalized and first normal form entity relationship diagrams for the computer system. Double click on the entities to view the repository information (in both Microsoft Visio and Visible Analyst. In Microsoft Visio the repository entry is in an area on the bottom of the display. You may have to drag the border separating the diagram from the repository upward. Click the Columns entry in the Categories area on the left side of the repository to view the entity attributes). The diagram name is COMPUTER SYSTEM – UNNORMALIZED.

2. Use Microsoft Visio or Visible Analyst to view the entity-relationship diagram for the computer system. Double click on the entities to view the repository information (in both Microsoft Visio and Visible Analyst). The diagram name is COMPUTER.

3. Add the VENDOR entity to the diagram. The vendor warrants the computers, and the relationship between VENDOR and COMPUTER is that one VENDOR can warrant many COMPUTER(s). Add primary keys. Microsoft Visio will automatically create foreign keys. In Visible Analyst, select Key Synchronization from the Repository menu.

4. Add the MAINTENANCE entity to the diagram. Maintenance repairs are performed on computers, and the relationship between MAINTENANCE and COMPUTER(s) is such that one COMPUTER may have many MAINTENANCE records. Use the repository to define MAINTENANCE ORDER NUMBER. Set this attribute as the primary key for MAINTENANCE entity and generate the foreign key.

5. Describe the SOFTWARE CATEGORY entity in the repository. Include the elements found on the entity-relationship diagram below SOFTWARE CATEGORY in the Composition area.

6. Describe the MAINTENANCE entity in the repository. The elements are as follows:

a. MAINTENANCE ORDER NUMBER.

b. HARDWARE INVENTORY NUMBER.

c. MAINTENANCE DATE.

d. TYPE OF MAINTENANCE.

e. COST OF MAINTENANCE.

f. MAINTENANCE COVERED BYWARRANTY.

7. Describe the VENDOR entity. The elements are as follows:

a. VENDOR NUMBER.

b. VENDOR NAME.

c. STREET.

d. CITY.

e. STATE.

f. ZIP CODE.

g. TELEPHONE NUMBER.

h. DATE LAST ORDER SENT.

i. TOTALAMOUNT PURCHASED FROM VENDOR.

j. TOTAL NUMBER OF ORDERS SENT TO VENDOR.

8. Each computer may have more than one operating system, and each operating system may be installed on more than one computer. Add an associative entity called COMPUTER OPERATING SYSTEM between COMPUTER and OPERATING SYSTEM. Include the primary and foreign keys in the repository in either Microsoft Visio or Visible Analyst.