Practical Issues in Database Management: A Reference for the by Fabian Pascal

By Fabian Pascal

3 a long time in the past relational expertise positioned the database box on a legitimate, clinical origin for the 1st time. however the database industry--vendors, clients, specialists, and the alternate press--has primarily flouted its rules, focusing as a substitute on a "cookbook," product-specific process, with out conceptual realizing. the results were expensive: DBMS items, databases, improvement instruments, and purposes not just do not constantly practice as much as expectation or power, yet they could inspire the inaccurate questions and supply the incorrect solutions.

Practical matters in Database administration is an try and treatment this intractable and dear scenario. Written for database designers, programmers, managers, and clients, it addresses the center, mostly habitual matters and difficulties that practitioners--even the main skilled database professionals--seem to systematically misunderstand, specifically:

Unstructured facts and intricate information kinds company principles and integrity enforcement Keys Duplicates Normalization and denormalization Entity subtypes and supertypes info hierarchies and recursive queries Redundancy Quota queries lacking info

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5 Index Files When a table is stored on disk, it is often referred to as a file. In this case, each row of the table is referred to as a record , and each column is referred to as a field. ) Since disk access is typically slow, an important goal is to reduce the amount of disk accesses necessary to retrieve the desired data from a file. Sequential searching of the data, record-by-record, to find the desired information may require a large number of disk accesses and is very inefficient. The purpose of an index file is to provide direct (also called random) access to data in a database file.

Table 4-5. A table with redundant data City Los Angeles StreetName Hollywood Blvd Vine St ZipCode 95000 95000 However, we can split this table scheme into two schemes: {ZipCode,City} and: {ZipCode,StreetName} In this case, Table 4-5 gets split into two tables, Tables Table 4-6 and Table 4-7, and the redundancy is gone! Table 4-6. First table derived from Table 4-5 to eliminate redundancy 56 TEAM FLY PRESENTS ZipCode 95000 City Los Angeles Table 4-7. Second table derived from Table 4-5 to eliminate redundancy ZipCode 95000 95000 StreetName Hollywood Blvd Vine St Generally speaking, the design of a database may begin with an E/R diagram.

Partial decomposition of Table 4-12 ISBN PageCount 0-111-11111-1 0-111-22222-2 500 500 Table 4-14. 95 Now here is the problem. Looking at the second table, we have no indication that the original scheme required that PageCount determine Price. 50, as we've done in Table 4-15. Table 4-15. 50 59 TEAM FLY PRESENTS But putting the tables back together for a look at all of the data gives us Table 4-16, which reveals a violation of the requirement that PageCount determine Price. In fact, somebody at the publishing company is going to be very unhappy that the company is now selling a 500-page book below cost!

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