Requirements Analysis, Part II
Tom Kelliher, CS 319
Nov. 6, 2000
Requirements analysis, part I.
- Method-based analysis.
- System contexts.
- Human, social, organizational contexts.
Application of a structured method to analysis process. Aided via CASE
``Set of steps,'' but no one method is applicable to all classes of systems.
Structured method components:
- Process model: Method activities. Presented as set of step, but in
actuality is an iterative process.
- System modelling notations: dataflow, entity-relational, OO, etc.
- Rules within models (entities must have names) and between models
(flows within a dataflow model must be represented with an
- Design guidelines to promote good design. ``An object should have no
more than five sub-objects.''
- Report templates defining how information collected during analysis
phase is presented.
The VORD method of requirements analysis:
Other methods: OO analysis, dataflow-based methods.
- Viewpoint identification: Discovering viewpoints which receive system
services and identifying specific services provided. Brainstorming to
determine viewpoints, services, data inputs, non-functional requirements,
control events, and exceptions.
- Viewpoint structuring: Grouping related viewpoints into a hierarchy.
Common services are provided at higher levels in the hierarchy. Lower
level viewpoints inherit.
- Viewpoint documentation: Refining viewpoints and services.
- Viewpoint system mapping: translation to OOD.
- What are the boundaries of the system? Interactions with what other
systems? Other systems: the ``environment.''
Usually clear-cut if the new system is replacing an existing system.
Not always: Consider whether to continue using a legacy database.
- Once initial boundaries have been set, perform initial analysis to
determine dependencies (simple block diagram of dataflow).
- Expand the simple model into a richer environmental model. Nail down
- Social and organizational forces may shape the system boundaries.
- People are resourceful; they become frustrated by systems which
impose particular ways of working.
- These factors affect all viewpoints. There is no systematic means
for deriving requirements for these factors.
Consider a system to allow senior management access to information,
bypassing middle managers. Consider the social and organizational factors
influencing the viewpoints.
- The study of people's work practices. Used to generate
- Impact upon requirements analysis. Consider an imperfect system
(railroad paradox): A service isn't good so users complain about and find
alternative services. Analysts then examine the system, determine that it
isn't being used, and decide it isn't necessary.
- Another example: Collision alert warning in air traffic control
system. Switched off due to warning's nuisance. A good idea, poorly
implemented. Simple-minded analysis would have it removed from the system.
- Ethnography and prototyping.
Start the VORD process for an online library catalog system. Identify
viewpoints, services, data inputs, non-functional requirements, control
events, and exceptions.
Thomas P. Kelliher
Thu Nov 2 14:21:14 EST 2000