Designing the inputs, outputs, processing, data storage and user interface of a system, and the design tools used: data flow diagrams, system flowcharts, entity relationship diagrams and the data dictionary.

What this dot point is asking

CCEA wants you to describe what is specified during the design stage, the inputs, outputs, processing, data storage and user interface, and to recognise the design tools used to document them: data flow diagrams, system flowcharts, entity relationship diagrams and the data dictionary. Design turns the requirements specification into a blueprint a developer can build from.

What gets designed

The elements a designer specifies are:

• Outputs. The reports, screens and documents the system produces, with their layout, content and format.
• Inputs. The data entering the system, its source, format and the screens or forms that capture it, including validation.
• Processing. The logic that turns inputs into outputs, including calculations, decisions and rules.
• Data storage. The files or database tables, their fields and the relationships between them.
• User interface. The menus, navigation, screen design and on-screen prompts the user sees.

The design tools

Each tool documents a different facet of the design, and together they form the design specification. A DFD gives the big picture of data movement; a flowchart drills into the logic of one process; an ERD captures the data structure; and the data dictionary pins down the precise definition of each field.

The data dictionary in detail

The data dictionary is metadata, data about the data. For each field it records the name, data type (for example integer, text, date, Boolean), length or size, valid range or format, the validation rule, and a short description. Because every designer, programmer and database builder reads the same dictionary, everyone uses identical field names, types and rules, which removes inconsistency and makes later maintenance far easier.

Why design before building

A complete design lets developers build with few surprises, lets testers write tests from the specified behaviour, and gives a reference for maintenance. Skipping design and coding straight from a vague requirement leads to rework, inconsistent data and features that do not match what users need.

Try this

Q1. Name the design tool that shows how data moves between processes, data stores and external entities. [1 mark]

• Cue. A data flow diagram (DFD).

Q2. List three pieces of information a data dictionary records about a field. [3 marks]

• Cue. Field name; data type; length or size; valid range or format; validation rule; description (any three).

Q3. Explain why designers often design the outputs of a system before the inputs. [2 marks]

• Cue. The required outputs determine what data must be captured and processed, so designing outputs first keeps the system focused on user needs and avoids capturing unused data.