6. Requirements analysis
(Preece: Chapter 19)
This chapter deals with requirements analysis - how functional, data and usability requirements are gathered - and documented.
- Functional requirements
- What the system must do
- Data requirements
- Structure of the system and data that must be available for the system
- Usability requirements
- The acceptance level of user performance and satisfaction with the system
Functional requirements
Basic design tools : Dataflow diagram and data dictionary
Symbols for dataflow diagram
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The source or destination of data (outside the system - typically the user - or some external equipment.
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The process that operates on the data
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Dataflow between two processes or between datastore and process
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The datastore - data base. Stored data that will remain in the file (data base) permanently.
Tha dataflow diagram is hierarchical - one process can be described in more detail by a dataflow diagram.
Data requirements
Data requirements can be expressed using Entity - Relationship models (See course on data models (Tietomallit) or Object Models (See course on Object modelling - Oliomallintaminen)
Usability requirements
Usability requirements determine the acceptance level for the system.
The requirements can be expressed in terms of
- Learnability
- The time and effort required to reach a specified level of performance
- Throughput
- The speed of task execution and the errors made
- Flexibility
- The extent to which the system can accomodate changes to the tasks and environments
- Attitude
- The positive attitude of users towards the system
The requirements should be stated in concrete terms.
Some possible requirements could be
- Time to complete task
- Ratio of successes to failures
- Time spent on errors
- Number of commands used
- Time spent searching for help
- Number of good and bad features of the system
- .....