Physical data independence

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  • Data Model: A set of concepts to describe the structure of a database, and certain constraints that the database should obey. Data Model Operations: Operations for specifying database retrievals and updates by referring to the concepts of the data model. Operations on the data model may include basic operations and user-defined operations.

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  • A crucial property of a relational DBMS is that it provides physical data independence. This allows physical structures such as indexes to change seamlessly without affecting the output of the query; but such changes do impact efficiency. Thus, together with the capabilities of the execution engine and the optimizer, the physical database design determines how efficiently a query is executed on a DBMS. The first generation of relational execution engines were relatively simple, targeted at OLTP, making index selection less of a problem.

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  • The minimum number of Cs that can be associated with one A is 1. I know this because the existence of the C to A relationship is mandatory. The maximum number of Cs that can be associated with one A is unlimited (or many). I know this because the cardinality of the C to A relationship is 1-M.

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  • Câu 1: A problem soling technique that decomposes a system its component parts while focusing on the business problem independent of technology is: a. Cause-and-effect analysis. b. System design. c. Joint application design(JAD). d. Systems analysis. Câu 2: A database is an organized collection of ____ related data. a. None of the others answers. b. logically. c. not. d. physically.

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