Chapter 2 · Data Organisation & Control
Hours: 4 · Difficulty: ★★☆☆☆ · Bridge to: Elective 2A Databases
Data is useful only when you can find it again and trust that it has not been corrupted. This chapter teaches you how raw data is structured (organisation) and how errors are prevented and detected (control).
Chapter contents
| # | Topic | Approx. study time |
|---|---|---|
| 2.1 | Hierarchy of data | 30 min |
| 2.2 | Sequential vs direct access | 45 min |
| 2.3 | Validation, verification & parity | 60 min |
Learning outcomes
- Identify data, records, fields, files and databases in the hierarchical organisation of data.
- Explain how records can be organised, stored and retrieved.
- State the advantages, disadvantages and applications of direct access and sequential access.
- Discuss the need for data control.
- Describe how errors can be detected by validation and parity checking, and prevented by verification and validation.
Why this chapter matters
- Foundation for Elective 2A — every term here recurs in databases.
- Form fields in SBA — you will design validation rules for your own system.
- Easy marks in Paper 1 — these short questions reliably appear in Section A.
Self-test before moving on
After this chapter you should be able to answer:
- List the 5 levels of the data hierarchy (smallest → largest).
- Give one situation where sequential access is faster than direct access.
- Distinguish a range check (validation) from a double-entry check (verification).
- Explain how even parity detects a 1-bit error.
➡️ Start with: 2.1 Hierarchy of data