Structured Analysis Lec 3 - tructured Systems Analysis:...

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Unformatted text preview: tructured Systems Analysis: tructured Systems Analysis: Structured Systems Analysis: Structured Systems Analysis: Transform Descriptions Transform Descriptions EGA/ERLJ IE 154 Objectives for Today r Know the need for Transform Descriptions r Know how to describe minispecs and policies r Draw and improve decision trees raw and improve decision tables r Draw and improve decision tables Introduction r We are looking at certain techniques which are used in the design of programs - particularly within the context of the design of software systems . r Remember that when we are talking here about rograms and software, we do not generally programs and software, we do not generally mean packaged software (the software you can buy in shops). r The larger part of the software in the world is custom-built , and typically the result of analysis and design methodologies. Diagram 1 Decomposition of DFDs r By a process of decomposition the system is first modeled in a structured and comprehensible form; and then that model is transformed into a set of transform descriptions . r Each of these transform descriptions is an lgorithm hether or not it describes a process algorithm - whether or not it describes a process which is going to be computerized. r Where a process is suitable for implementation in software, we now have a specification (minispecs) for that software component - ie: a specification for a (small) piece of program code. Review r A functional primitive is a bubble which: c Cannot be partitioned or leveled further, that is, it has no internal data flows, or c has a single input and a single output, or c is “suitable small” and can be described in a page or less Transform Descriptions r In the structured specification, the logic of processes is defined only at the functional primitive level. r Process logic or policy descriptions are done by making a minispec for each functional primitive. r Each minispec usually covers a single page of the description of the process Objectives for Today r Know the need for Transform Descriptions r Know how to describe minispecs and policies r Draw and improve decision trees raw and improve decision tables r Draw and improve decision tables How do we describe Minispecs? r A natural language such as English is imprecise, verbose, redundant, and full of implications and connotations. A natural language is not ideal for specification purposes. c “If the total value of a given sales order exceeds the threshold value of the given customer, the sales order is rejected, otherwise it is accepted” How do we describe Minispecs? r Programming languages on the other hand are much too strict or specific for the purpose of defining the policy or decisions in a process....
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Structured Analysis Lec 3 - tructured Systems Analysis:...

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