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OMIS2000- Chapter Notes

Ring topology connects network components in a closed

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Unformatted text preview: ents data as they would be perceived by end users or business spets Physical view – shows how data are actually organized and structured on physical storage media How a DBMS solves the problem solves the problem of the traditional file environment: - Reduces data redundancy an inconsistency by minimizing isolated files in which the same data are repeated - Uncouples programs and data, enabling data to stand on their own - Access and availability are improved and program development and maintenance costs are reduced b/c end users can perform ad hoc queries of data in the database. - Enables the org to centrally manage data, their use, and security through a data dictionary. Relational DBMS – represent data as 2- D tables/files called relations. Fields in a relational database are also called columns. The actual info about a single entity that resides in a table is called a row. Rows are commonly referred to as records/tuples. Key field – unique identifier of an entity. Ex. SUPPLIER Supplier_Number Primary key – unique identifier for all the info in any row of the table and this primary key cannot be duplicated. OMIS 2000 Final Exam Gahtan 18 If an attribute appears in more than one table, it is a key field in one but a foreign key in the other. E.x. Supplier_Name is a key field for SUPPLIER but a foreign key for PARTS (page 182) In a relational database, three basic operations are used to develop useful sets of data: select, join, and project. Select – creates a subset consisting of all records in the file that meet stated criteria. Ex. in...
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