Software Engineering-Comparison of Design notation


We presented a number of different techniques for representing a procedural design. A comparison must be predicated on the premise that any notation for component-level design, if used correctly, can be an invaluable aid in the design process; conversely, even the best notation, if poorly applied, adds little to understanding. With this thought in mind, we examine criteria that may be applied to compare design notation.

Design notation should lead to a procedural representation that is easy to understand and review. In addition, the notation should enhance "code to" ability so that code does, in fact, become a natural by-product of design. Finally, the design representation must be easily maintainable so that design always represents the program correctly.

The following attributes of design notation have been established in the context of the general characteristics described previously:

Modularity. Design notation should support the development of modular software and provide a means for interface specification.

Overall simplicity. Design notation should be relatively simple to learn, relatively easy to use, and generally easy to read.

Ease of editing. The procedural design may require modification as the software process proceeds. The ease with which a design representation can be edited can help facilitate each software engineering task.

Machine readability. Notation that can be input directly into a computer-based development system offers significant benefits.

Maintainability. Software maintenance is the most costly phase of the software life cycle. Maintenance of the software configuration nearly always means maintenance of the procedural design representation.

Structure enforcement. The benefits of a design approach that uses structured programming concepts have already been discussed. Design notation that enforces the use of only the structured constructs promotes good design practice.

Automatic processing. A procedural design contains information that can be processed to give the designer new or better insights into the correctness and quality of a design. Such insight can be enhanced with reports provided via software design tools.

Data representation. The ability to represent local and global data is an essential element of component-level design. Ideally, design notation should represent such data directly.

Logic verification. Automatic verification of design logic is a goal that is paramount during software testing. Notation that enhances the ability to verify logic greatly improves testing adequacy.

"Code-to" ability. The software engineering task that follows component-level design is code generation. Notation that may be converted easily to source code reduces effort and error.

A natural question that arises in any discussion of design notation is: "What notation is really the best, given the attributes noted above?" Any answer to this question is admittedly subjective and open to debate. However, it appears that program design language offers the best combination of characteristics. PDL may be embedded directly into source listings, improving documentation and making design maintenance less difficult. Editing can be accomplished with any text editor or word-processing system, automatic processors already exist, and the potential for "automatic code generation" is good.
However, it does not follow that other design notation is necessarily inferior to PDL or is "not good" in specific attributes. The pictorial nature of flowcharts and box diagrams provide a perspective on control flow that many designers prefer. The precise tabular content of decision tables is an excellent tool for table-driven applications.
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