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2 - Data Organization

M cheung william tan and carson woo 27 busi 335

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Unformatted text preview: pyright © 2009-10 Y.M. Cheung, William Tan and Carson Woo 28 Economic Relations between Access Methods between Access Methods Comparison of Access Methods Comparison of Access Methods Factor Storage Space Sequential Indexed Access Sequential Access No wasted No wasted space space for data, but extra space for index Very Fast Moderately fast Sequential Retrieval on Primary Key Random Impractical Retrieval on Primary Key Primary Key Adding New Requires Records rewriting file file BUSI 335 Direct (Random) Access Extra space may be needed to resolve conflict of addresses Impractical The basic economics of file processing are basic economics of file processing are largely determined by the activity ratio. activity What is the activity ratio? It is the number of accessed records divided by the number of records in the file. Moderately fast Very fast Requires maintenance of indexes indexes Very easy, except multiple keys with same address require extra work require extra work Copyright © 2009-10 Y.M. Cheung, William Tan and Carson Woo 29 The second economic consideration concerns response time concerns response time. BUSI 335 Economic Relations between Access Methods between Access Methods • Defines specific storage structures and data access characteristics of the database, and is therefore hardware dependent. It is the length of time the user must wait for the system to comp...
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