solutions-04 - SOLUTIONS - CIS209 - INTERNAL - 2004...

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SOLUTIONS - CIS209 - INTERNAL - 2004 QUESTION 1 Part 1 Define the following terms (one or two sentences per term): a) Data [1] b) Database [1] c) Database Management System [1] d) Security [1] e) Integrity [1] f) Views. [1] Data: For end users, this constitutes all the different values connected with the various objects/entities that are of concern to them. Database: A shared collection of logically related data, and a description of this data, designed to meet the information need of an organization. Database Management System: A software system that enables users to define, create, maintain, and control access to databases. Security: The protection of the database from unauthorized users, which may involve passwords and access restrictions. Integrity: The maintenance of the validity and consistency of the database by use of particular constraints that are applied to the data. Views: These present only a subset of the database that is of particular interest to a user. Views can be customized, for example, field names may change, and they also provide a level of security preventing users from seeing certain data. Marking scheme: award 1 mark per correctly defined term. Part 2 Describe the concept of data independence in the three-level ANSI/SPARC architecture of database management system. Illustrate the concept with examples. [4] There are two kinds of data independence, namely logical and physical. The logical independence refers to the immunity of the external schemas to changes in the conceptual schema. Fore example changes such as the addition or removal of new entities, attributes or relationships, should be possible without having to change the external schema or to rewrite the application programs. CIS209 – IS52003A 2004 Internal Solutions 1
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The physical independence refers to the immunity of the conceptual schemas to changes in the internal schema. For example using different file organisations or storage structures, using different storage devices, modifying indexes should be possible without having to change the conceptual or external schemas. Marking scheme: award 2 marks for the description of data and physical independence. Part 3 Informally define each of the following concepts in the context of the relational data model: a) Relation [1] b) Intension [1] c) Cardinality . [1] a) Relation: is a table with columns and rows in which structured data is stored. b) Intension: is the structure of a relation plus the domains and the restrictions on possible values, which, in general, is fixed in time. c) Cardinality (of a relation): is the number of tuples in the relation. Marking scheme: award 1 mark per appropriate answer. Part 4 a) Describe in brief the approach taken to the handling of data in the early file-based systems. Discuss the disadvantages of this approach.
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This note was uploaded on 05/13/2010 for the course COMPRO CS401 taught by Professor Just during the Spring '10 term at Maharishi.

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solutions-04 - SOLUTIONS - CIS209 - INTERNAL - 2004...

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