7830TextAnswersCh8

7830TextAnswersCh8 - Chapter Eight Database Redesign...

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Chapter Eight Database Redesign Page 8-1 ANSWERS TO REVIEW QUESTIONS 8.1 Explain, one more time, the three ways that databases arise. Databases are created (1) from existing data, (2) form the development of new information systems, and (3) form the redesign of existing databases. 8.2 Describe why database redesign is necessary. Database design involves taking a set of requirements and creating from scratch a database design. Database redesign involves taking an existing database and making changes to the structure of that database to add requirements or improve performance. It is not so easy to build a database correctly the first time. Even if we can obtain all of the users’ requirements, the tasks of building a correct data model and of transforming that data model into a correct database design are difficult. During those stages, some aspects of the database will need to be redesigned. Also, inevitably, mistakes are made that must be corrected. When a new information system is installed, the users can behave in new ways. As the users behave in those new ways, they will want changes to the information system to accommodate their new behaviors. As those changes are made, the users will have more new behaviors, they will request more changes to the information system, and so forth in a never- ending cycle. 8.3 Explain the following statement in your own words: "Information systems and organizations create each other." How does this relate to database redesign? When a new information system is installed, the users can behave in new ways. As the users behave in those new ways, they will want changes to the information system to accommodate their new behaviors. As those changes are made, the users will have more new behaviors, they will request more changes to the information system, and so forth in a never- ending cycle. 8.4 Suppose that a table contains two nonkey columns: AdvisorName and AdvisorPhone. Further suppose that you suspect that AdvisorPhone Æ AdvisorName. Explain how to examine the data to determine if this supposition is true. Check the table to determine if each AdvisorPhone has only one value of AdvisorName. If the AdvisorPhone appears in the table more than once and the AdvisorName is not the same, AdvisorPhone does not determine AdvisorName. You can use a correlated subquery to determine this. 8.5 Write a subquery, other than one in this chapter, that is not a correlated subquery. We’ll use the View Ridge Gallery database for this example. For SQL Server: SELECT C.CustomerID FROM CUSTOMER C WHERE C. CustomerID IN (SELECT I.CustomerID FROM CUSTOMER_ARTIST_INT I WHERE I.ArtistID = 14);
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Chapter Eight Database Redesign Page 8-2 8.6 Explain the following statement: The processing of correlated subqueries is nested, whereas that of regular subqueries is not.
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This note was uploaded on 09/13/2009 for the course CS CS31 taught by Professor Camillo during the Spring '09 term at Grantham.

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7830TextAnswersCh8 - Chapter Eight Database Redesign...

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