5. Design methods

(Preece: Chapters 17,18) 
This chapter deals with design methods suitable for the design of interactive systems - human centered desing. The basic principles of information system design are of course valid here. We take a look at traditional waterfall model of system development and also at some more user oriented principles 

The waterfall model of software development

Application description
General description of the purpose and the functions of the system to be designd
Requirements specification
Detailed description of the function the systems should perform
System design
Defining the software functions and software modules
The resulting implementation of the system
The waterfall model assumes that the design is fixed before entering to the next phase of design. Does not fit well in interactive systems. 

The Soft Systems Methodology

(Checkland : Systems Thinking Systems Practice, 1981) 
Checklands soft systems methodology emphasizes the role of a system in solving problems in the use situation - in the organization that will use the system. 

The problem situation
Find out the stakeholders of the situation
The problem situation expressed
Detailed description of different opinions about the problem - suggestions for solutions
Definitions of the system
Design on the software system
Conceptual model
Model of the resulting system - its basic concepts - abstract representation of the system
Comparison of 4 with 2
Is the design a solution?
Feasible and desirable changes
How the system changes the situation
Actions to improve the situation
The consequenses of implementing the system and taking it in use

Keywords in SSM = CATWOE

The Star Model

(Hartson and Hix: Developing User Interfaces, 1993) 
The design of interactive systems typically does not follow a specific order of steps.
The design can start in any step - followed by evaluation
Design emphasizes rapid prototyping
Alternating waves of analytic (top-down) and synthetic (bottom-up) design steps
Needs good software tools