7.2 Design

2026 Syllabus Objectives

  • Design file/data structures, input formats, output formats and validation routines
  • Understand file/data structures including field length, field name, data type, coding of data (e.g., M for male, F for female)
  • Implement validation routines including range check, character check, length check, type check, format check, presence check, check digit
  • Design input formats including data capture forms
  • Design output formats including screen layouts and report layouts

File and Data Structures 📂

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When developing a new system, one of the critical first steps is to finalize the file structure. This is particularly important for systems that contain files such as databases.

Key Components of File Structure

The file structure needs to be determined before the system is created and tested. This involves making decisions about several important elements:

Field Name 🏷️

  • The identifier used to describe what data is stored in a particular field
  • Should be descriptive and meaningful
  • Example: CustomerName, DateOfBirth, PhoneNumber

Data Type 📊

  • Specifies what type of data is being stored in each field
  • Common data types include:
    • Text/String (for names, addresses)
    • Numeric (for quantities, prices)
    • Date/Time
    • Boolean (True/False)
  • Ensures that only appropriate data can be entered into each field

Field Length 📏

  • Determines the maximum number of characters that can be stored in a field
  • Must be carefully chosen to accommodate all valid data while preventing excessively long entries
  • Example: A postcode field might have a length of 8 characters

Key Field 🔑

  • A specific field within a file structure used to uniquely identify records
  • Also known as a primary key
  • Ensures that each record in the database can be distinguished from all others
  • Example: A customer ID number or student registration number

Data Coding 💾

  • Using abbreviated codes to represent data efficiently
  • Saves storage space and standardizes data entry
  • Examples:
    • Gender: M for male, F for female
    • Days: Mon, Tue, Wed, etc.
    • Status codes: A for active, I for inactive

Linking Data Files 🔗

  • Determining how different data files or tables will be connected
  • Uses key fields to establish relationships between tables
  • Essential for relational database design

Important: Once the file structure has been determined, it must be created and fully tested to make sure it is robust when the system actually goes live.

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