Chapter 5. Requirements analysis
-. Requirements analysis is a difficult process for a number of reasons :
(1) Stakeholders often don't really know what they want from the computer system
except in the nost general terms.
(2) Stakeholders in a system naturally express requirrements in their own terms and
with implicit knowledge of their own work.
(3) Different stakeholders have different requirements and they may express these
in quite different ways.
(4) Analysis takes place in an organizational context. Political factors may influence
the requirements of the system.
(5) The economic and business environment in which the analysis takes place is
-. The analyst's understanding of the requirements improves with each round of the
cycle. The process activities are :
(1) Domain understanding
(2) Requirements collection
(4) Conflict resolution
(6) Requirements validation
5.1 Viewpoint-oriented analysis
-. For any medium-sized or large system, there are usually different types of end-users,
-. Viewpoints are implicitly recognized in analysis methods such as SRD and SADT.
-. A viewpoint may be considered as :
(1) A data source or sink
(2) A representation framework
(3) A receiver of services
-. The advantages of external viewpoint are :
(1) In the majority of inteeractive systems, it in natural to think of end-users as
receivers of system services.
(2) Because they are external to the system, viewpoints are a natural way to
structure the requirements elicitation process.
(3) It is relatively easy to decide if some agent is or is not a valid viewpoint.
(4) Viewpoints and services are a useful way of structuring non-functional
5.2 Method-based analysis
-. Structured methods usually include some or all of the following :
+. A process model
+. System modelling notations
+. Rules applied to the system model
+. Design guidelines
+. Report templates
-. Objected-oriented analysis and data-flow based nethods are fairly widely used.
-. The reason for this is that structured methods based on computational models are
-. The first three stages of the VORD method are concerned with viewpoint and service
identification, viewpoint structuring and documentation.
5.3 System contexts
-. Once some decisions on the boundaries of the system have been made, part of the
analysis activity is to define that context and the dependencies which a system has
on its environment. Normally, producing a simple block diagram is the first step in this
-. The definition of a system context is not, of course, a value-free judgement.
5.4 Social and organizational factors
-. Factors which might affect the requirements for this sytem are :
(1) The manager's status.
(2) The manager's responsibilities.
-. The social analysis is based on a technique called ethnography, whereby
a sociologist spends a considerable amount of time in the working environment.
-. Railroad paradox
: A service isn't good so users complain about it. They find alternatives to the
service (e.g. cars) so it isn't used much. In response to the complaints, analysts
examine how the system is used, find it isn't popular so decide that it isn't