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Organizing Data Chapter 5
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Data Hierachy
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Table = Entities X Attributes Entities = Records Attributes = Fields
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Files vs. Databases In the 70’s and early 80’s Information Systems used files to store data “Traditional Approach” In the mid-80’s “The Database Approach” became the standard Traditional Appoach –Data redundancy –Application dependent on data format and vice versa.
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Traditional Approach
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Database Approach MIS DBMS
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Hierarchical Models
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(E-R) Entity-Relatonship Diagrams
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Network Model
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Relational Model Find the name and hire date of the manager working on the sales manual project
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Schemas Schema - A description of the database Subschema – describes a subset of the database and which users have access to this subset
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Data Definition Language Defines the data in a Database Describes relationships between different data Provides a Logical view of the data Used to describe Schemas and Subschemas
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Data Dictionary Entry A more detailed description of the data in a database Specifies data types and ranges Assists programmers in understanding the data
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Logical vs. Physical Access Paths Database Management Systems concentrate on Physical access to the underlying tables –Concurrency control –Query’s –Creating/deleting tables MIS systems are often software packages that (Logically) interface with a DBMS –monthly reports –charts –automated inquiries
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