INFO90002 Chap.4 Logical Design and Normalisation

Logical Design and Normalisation

Logical Design and Normalisation turns functional dependency, normal forms and lossless decomposition into executable reasoning. The chapter's practical target is to remove update anomalies while preserving meaning and joinability, so every explanation should connect syntax to program state, control flow and observable output.

Treat functional dependency as a precise program object, not a loose label.

Identify its value or responsibility before execution, then trace what can read it, change it or depend on it. This makes hidden state changes visible before they become debugging guesses.

Use normal forms to explain the program's next move. Work through one representative input by hand and name the branch, iteration or call that follows.

If the trace cannot be stated, the code may run by accident rather than by understood design.

Bring in lossless decomposition as the test of structure.

Compare normal, boundary and invalid inputs; state the expected behaviour first; then use the mismatch between expectation and result to localise the defect.

For the application — remove update anomalies while preserving meaning and joinability — write the smallest complete example that exposes the rule.

Explain why it works, what would break it and how the program should signal or recover from that failure.

Before running a Logical Design and Normalisation example, make a trace table with the important state before and after each operation. Include the value associated with functional dependency, the control decision governed by normal forms and the output or object affected by lossless decomposition.

The table turns an unexplained result into a sequence that can be tested one transition at a time.

Test three inputs: an ordinary case, a boundary case and an invalid case. State the expected result for each before execution, then compare it with what the program actually does.

A useful test of normal forms isolates one rule; a test that changes several conditions at once cannot tell you which condition caused the failure.

Practise explaining the solution without reading the code. For INFO90002, name the data representation, the control flow, the responsibility of each function or class and the reason the chosen design supports remove update anomalies while preserving meaning and joinability.

This rehearsal is especially important when a written test or interview asks why the program works rather than whether it produces one correct output.

A complete Logical Design and Normalisation response should make the task visible before the detail: identify what must be decided, define the relevant terms, connect the evidence to normal forms, and use lossless decomposition to test the result.

The final sentence should answer the question actually asked rather than merely repeat the topic.

The controlling limit is specific: Normalisation is not a mechanical ban on every repeated-looking value.

Keep that limit beside the worked example, because it separates a careful INFO90002 answer from one that sounds confident but claims more than the task or evidence supports.

For revision, retrieve functional dependency, normal forms and lossless decomposition without notes, explain their relationship aloud, then complete a changed version of the application: remove update anomalies while preserving meaning and joinability.

Record the first point at which your reasoning fails and repair that move before attempting another case.

What this chapter covers

• 01

  functional dependency

• 02

  normal forms

• 03

  lossless decomposition

• 04

  Applying functional dependency

• 05

  Limits of normal forms and lossless decomposition

Worked example: Logical Design and Normalisation

Key terms

normalisation

Normalisation decomposes relations according to functional dependencies to reduce redundancy and prevent insertion, update and deletion anomalies while preserving required information. In this chapter, use the concept when you remove update anomalies while preserving meaning and joinability.

conceptual, logical and physical design (the database development lifecycle)

Conceptual design models business entities and relationships independently of technology, logical design translates them into a data model and constraints, and physical design specifies storage, indexes and implementation details. In this chapter, use the concept when you remove update anomalies while preserving meaning and joinability.

DDL, DML and DCL (CREATE/DROP/ALTER vs SELECT/INSERT/UPDATE/DELETE vs GRANT/REVOKE)

DDL defines database structures with commands such as CREATE, ALTER and DROP; DML queries or changes data with SELECT, INSERT, UPDATE and DELETE; DCL manages privileges with GRANT and REVOKE. In this chapter, use the concept when you remove update anomalies while preserving meaning and joinability.

Logical Design and Normalisation FAQ

Exam move

Reconstruct the relationship among functional dependency, normal forms and lossless decomposition; complete the chapter application without notes; then test the result against this limit: Normalisation is not a mechanical ban on every repeated-looking value.

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