Assngment

ANSWERS TO REVIEW QUESTIONS 6

1. What are multivalued attributes, and how can they be handled within the database design?

As the name implies, multi-valued attributes may have many values. For example, a person's education may include a high school diploma, a 2-year college associate degree, a four-year college degree, a Master's degree, a Doctoral degree, and various professional certifications such as a Certified Public Accounting certificate or a Certified Data Processing Certificate.

There are some ways to handle multi-valued attributes, and some of those ways may not be preferred:

1. Each of the possible outcomes is kept as a separate attribute within the table. This solution is undesirable for several reasons. First, the table would generate many nulls for those who had minimal educational attainments (beceri, yetenek). Using the preceding example, a person with only a high school diploma would generate nulls for the 2-year college associate degree, the four-year college degree, the Master's degree, the Doctoral degree, and for each of the professional certifications. In addition, how many professional certification attributes should be maintained? If you store two professional certification attributes, you will generate a null for someone with only one professional certification and you'd generate two nulls for all persons without professional certifications. And suppose you have a person with five professional certifications? Would you create additional attributes, thus creating many more nulls in the table, or would you simply ignore the additional professional certifications, thereby losing information?

2. The educational attainments may be kept as a single field (variable-length string or character field). This solution is undesirable because it becomes difficult to query the table (ask a question). For example, even a simple question such as "how many employees have four-year college degrees?" requires string partitioning that is...