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Database Concepts and Entity Relationship Modelling

What a database is and why one is used

  • 3 things to know
  • A2 Unit 1

Overview

Database management system, data redundancy and data inconsistency.

What you need to know

Answer each one before you reveal it.

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Key term

What is a database management system?

Key term

What is a schema?

Key term

How does a database control who may see what?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is a database?

    Model answer

    A database is an organised, persistent collection of related data held so that more than one application can use it, with the structure of the data defined separately from the programs that read and write it.

  2. 2

    What is a database management system?

    Model answer

    A database management system is the software that creates and maintains the structure of a database, enforces its rules, controls who may see and change what, and processes queries and updates on behalf of applications.

  3. 3

    Why is storing data in application files a poor arrangement?

    Model answer

    Each application defines its own file layout, so the same fact is stored separately by each of them. Storage is wasted, an update applied to one file and not another leaves them contradicting each other, and no application can answer a question that spans two of the files.

  4. 4

    What is data redundancy?

    Model answer

    Data redundancy is the storage of the same item of data in more than one place. Redundancy wastes space and, more importantly, creates the opportunity for the copies to disagree.

  5. 5

    What is data inconsistency?

    Model answer

    Data inconsistency is the state in which two stored copies of the same fact disagree, because one was updated and the other was not. Redundancy is the cause and inconsistency is the consequence.

  6. 6

    What is meant by data integrity?

    Model answer

    Data integrity is the accuracy and internal consistency of the stored data over its whole life, maintained by validation on entry, by rules linking one table to another, and by controls that prevent unauthorised or partial change.

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Software and the Development Environment
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