JSP is one of the two design methods described in this book that have emerged from ideas and experiences of Michael Jackson. It has been chosen as the second detailed example of a software design method for the following reasons. It has limited and define applications, which make it possible to describe it more concisely yet fully than most other design methods. Ever since its development in the early 1970s it has been widely used, and therefore has a historical claim to be discussed in depth.
It is an excellent example of the use of a compositional design strategy.
It is well documented and widely used. However, some of the attributes that make JSP so valuable for developing ideas about design also have the potential to mislead. Because of its limited domain of application,
JSP provides more prescriptive forms of design transformation than almost any other systematic design method, and this makes it possible to incorporate a greater degree of verification than is generally practicable with other methods. JSP is essentially a program design method. It is concerned with the design of systems that are realizable as a single sequential process; have well-defined input and output data streams. JSP is therefore particularly well-suited to developing systems that employ a pipe and- filter architectural style. Despite this, while historically it has often been viewed as primarily of interest to the data-processing community, its use is by no means restricted to such problems, as will be illustrated here by examples and in the discussion in the final section. Indeed, because it is a program design method, there is scope to employ it in larger system design practices: one such example is SSADM
JSP representation forms Since the forms of representation that are used in JSP have already been described in considerable detail the discussion of this section will be kept to a minimum.JSP is unusual as a design method, in that it uses only a single diagrammatical form in its transformations. where its use for describing the sequences involved in both static data structures and dynamic program behavior was demonstrated. It is used in JSP for modeling both the structures of the data objects of interest, and the functional structuring of the program( s) that manipulate them. as examples of Structure Diagrams being used in both these roles; the rules for drawing them are shown in the box below.
Jackson Structured Programming (JSP)
Because JSP is concerned with program design, it places a strong emphasis on the development of algorithms, and the detailed forms for these are usually better described through the use of text. So JSP also makes use of pseudo code forms for the later stages of design, with these being derived from the diagrammatical forms as a part of the design transformation process. Some rules for drawing Structure Diagrams
· sequence is represented by unmarked boxes
· selection is represented by boxes marked with circles
· iteration is represented by an asterisked box
· sequencing is from left to right
· the three forms may not be mixed in a sequence
· the last selection part should always be condition less (the ELSE clause).
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