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Databases

Logical and physical data models

  • 3 things to know
  • A2 Unit 1

Overview

Logical data model, physical data model and conceptual data model.

What you need to know

Answer each one before you reveal it.

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Key term

Why should a date be stored as a date rather than as text?

Key term

What is a logical data model?

Key term

State the difference between a logical and a physical data model.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is a logical data model?

    Model answer

    A logical data model describes what data the system must hold and how it is related, expressed as entities, attributes and relationships. A logical model is independent of any particular database product, operating system or storage arrangement.

  2. 2

    What is a physical data model?

    Model answer

    A physical data model describes how the logical model will actually be implemented in a chosen database management system, naming tables and columns, fixing data types and sizes, and specifying keys, indexes and storage.

  3. 3

    State the difference between a logical and a physical data model.

    Model answer

    A logical model states what must be stored and how it relates, in terms a user could check; a physical model states how it will be stored in a named product, in terms a developer will implement.

  4. 4

    Why is a logical model produced before a physical one?

    Model answer

    Producing the logical model first forces the structure to be agreed with the users while it is still cheap to change, and keeps design decisions about the business separate from decisions about technology, which may be revisited later.

  5. 5

    Give three things a physical model specifies that a logical model does not.

    Model answer

    A physical model specifies the data type and size of every column, the indexes to be created, and the physical file or tablespace arrangement, together with the exact table and column names allowed by the chosen product.

  6. 6

    What is a conceptual data model?

    Model answer

    A conceptual data model is the highest level view, identifying the main entities of an organisation and the relationships between them without attributes or keys, and is used to agree scope before detailed analysis begins.

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