Consistent if a student changed his if phone number

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Unformatted text preview: nsistent If a student changed his If phone number, it may have been updated in one master file but not another. another. FILE VS. DATABASES Database Fact A Fact B Fact C Fact D Fact E Fact F Database Management System Enrollment Program Chapter 13-11 Financial Aid Program Grades Program The database approach The treats data as an organizational resource that should be used by and managed for the entire organization, not just a particular department. particular A database management system (DBMS) serves as the (DBMS) interface between the database and the various application programs. programs. IMPORTANCE AND ADVANTAGES OF IMPORTANCE DATABASE SYSTEMS DATABASE The importance of good data: Bad data leads to: Bad decisions Embarrassment Angry users Data Warehousing Institute estimates that dirty data costs $600 billion per year in unnecessary postage, marketing costs, and lost customer credibility. (Data scrubbing) Chapter 13-12 DATABASE SYSTEMS Logical and physical views of data In In file-oriented systems, programmers must know the physical location and layout of records used by a program. used They They must reference the location, length, and format of every field they utilize. every When data is used from several files, this process When becomes more complex. becomes Chapter 13-13 DATABASE SYSTEMS Database Database systems overcome this problem by separating the storage and use of data elements. elements. Two separate views of the data are provided: Logical view • How the user or programmer conceptually organizes and understands the data. Chapter 13-14 DATABASE SYSTEMS Database Database systems overcome this problem by separating the storage and use of data elements. elements. Two separate views of the data are provided: Logical view Physical view • How and where the data are physically arranged and stored. Chapter 13-15 Logical View—User B Logical View—User A Scholarship Distribution Enrollment by Class Sr. 33% Fr. 5% Soph. 24% Jr. 38% DBMS Operating System Database Chapter 13-16 The DBMS translates users’ logical views into instructions as to which data should be retrieved from the database. DATABASE SYSTEMS The The DBMS handles the link between the physical and logical views of the data. physical Allows Allows the user to access, query, and update data without reference to how or where it is physically stored. physically The user only needs to define the logical data The requirements. requirements. Chapter 13-17 DATABASE SYSTEMS Schemas A schema describes the logical structure of a schema database. database. There are three levels of schema. Conceptual level External level (subschema) Internal level Chapter 13-18 DATABASE SYSTEMS The The DBMS uses the mappings to translate a request by a user or program for data (expressed in logical names and relationships) into the indexes and addresses needed to physically access the data. data. Chapter 13-19 DATABASE SYSTEMS Accountants Accountants are frequently involved in developing conceptual- and external-level schema. schema. An employee’s access to data should be ’s limited to the subsch...
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