Systems

Problems and Exercises

Consider the E-R diagram in Figure 7-20. Based on this E-R diagram, answer the following questions:

a. How many EMPLOYEES can work on a project?

In this entity, an employee can only work on one-to-many projects

b. What is the degree of the Used on relationship?

It has a binary relationship degree

c. Do any associative entities appear in this diagram? If so, name them.

No. There are no associative entities.

d. How else could the attribute Skill be modeled?

The attribute skill could be modeled either as attributive or weak entity. Since only one-to-one and many-to-many are allowed to have associative attribute, this one cannot be modeled.

.

e. What attributes might be attached to the Works on relationship?

The only many-to-many relationship, since works on has no attribute, does not require to be shown as an associative entity.

f. Could TOOL be modeled as an associative entity? Why or why not?

The tool could be in be modeled in associative way as it falls in an associative entity because at the intersection of mandatory binary relationships between project, tool, and city, depending on the meaning of task. The tool has its own keys that are independent to the project keys (project, city and tool). For this reason, the tool can be modeled. However if the tool was modeled as an associative entity, some of important information would be lost.

16. The owner of two pizza parlors located in adjacent towns wants to computerize and integrate sales transactions and inventory management within and between both stores. The point-of-sale component must be easy to use and flexible enough to accommodate a variety of pricing strategies and coupons. The inventory management, which will be linked to the point-of-sale component, must also be easy to use and fast. The systems at each store need to be linked so that sales and inventory levels can be determined instantly for each store and for both stores combined. The owner...