Chapter 55 Data Modelling - Introduction
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Transcript of Chapter 55 Data Modelling - Introduction
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Chapter 55 Data Modelling - Introduction
Compiled by Eddie MoorcroftSource: P M Heathcote A level ICT
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Traditional file approach• Most organisations began information
processing on a small scale, by computerising each department independently, one by one.
• Files of information relevant to one department were created and processed by dozens of separate programs.
• This led to many problems:-
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Problems with traditional approach:
• Data redundancy– The same data duplicated in many
different files.• Data inconsistency
– Data that is duplicated, and not updated when changed in all files
• Program-data dependence– The computer program requires the data
to be in a particular format, changing the format requires every program using that file to be changed.
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Problems with traditional approach - continued• Lack of flexibility
– In such a system, when information of a non-routine nature is needed, it may take weeks to assemble the data from various files.
• Data not shareable– If one department has data that was
required by another, it can be awkward to obtain it.
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The database approachThe database approach• A database is defined as:
“a collection on non-redundant data shareable between different applications”
• Thus, all data belonging to the entire organisation would be centralised in a common pool of data, accessible by all applications.
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Problems with the Database approach• Unproductive maintenance
– Programs still depend on the structure of data files, so if one department required to add an extra field, all programs would need to be altered.
• Lack of security– All the data in the database, even
confidential or sensitive data, is accessible by all applications.
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The Database Management System (DBMS)• This is a layer of software inserted
between the applications and the data, which attempts to solve the problems of “Unproductive maintenance” and “Lack of Security”
• Two features of DBMS are:– Program-data
independence– Restricted user access
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Diagram of DBMS System
CompanyDatabase
DatabaseManage-
mentSystem
Salesprograms
Purchasingprograms
Financeprograms
Payrollprograms
Personnelprograms
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Conceptual data model• A database is designed based on the
information it will hold. The requirements are defined in terms of:
• An entity– a thing of interest to an
organisation, about which the data is to be held – e.g. customer, employee, stock item, etc.
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Conceptual data model - continued
• An attribute– a property or characteristic of an
entity – e.g. attribute associated with a student are, surname, forename, date of birth, admission number etc.
• A relationship– the links or association between
two entities, e.g. between school and pupil, a school contains many pupils, but a pupil only goes to one school.
Joe Bloggs,25/03/83,012345
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Entity-relationship diagrams
Employee Company cardrives
(One to One)
Ward Patientsholds(One to Many)
CD Album Singersfeatures
(Many to Many)