Ensayo De Analisis

Teaching design principles in software engineering
Jocelyn Armarego & Geoffrey G Roy
School of Engineering Science Murdoch University, Australia The teaching of program design skills to novices is a core problem in software engineering education. This paper discusses the need to develop a good understanding of the fundamental computational principles and identifies some of the key designskills that should be developed by students. The paper proposes that a pseudocode based model has some useful properties in enabling these skills to develop through top down design and through progressive refinement. To demonstrate and test these ideas a pseudocode tool, P-Coder, has been developed. This tool provides both graphical and textual elements in an interactive tree structured model. Much ofthe semantics of a program can be developed graphically before it is necessary to introduce formal programming language syntax. P-Coder also provides capabilities to insert code segments, which, when combined with the visual model, enable complete (Java) programs to be created. P-Coder is not intended to be a production environment, but rather a tool for developing both knowledge ofcomputational concepts and skill in program design. A preliminary evaluation of student results shows a clear improvement and suggests the approach is worth pursuing. Keywords: programming, program visualisation, program design, algorithm design

Introduction
Design skills are fundamental to all Engineering disciplines; in fact it is an ability to design that is often used to characterise engineers fromother disciplines. In broad term we think of design skills being related to the ability to: • • • • abstract from specific cases to more general situations recognise patterns in both process and product apply systematic techniques to problem solving, and apply, and adapt, tools and technologies to new problems.

Learning design skills is, however, a non-trivial problem: there are no simple meansof teaching them and assessing their development in a totally objective way. Design remains, as perhaps it should, a part of the art that makes an engineer a designer. In this paper we focus on the design of software, and in particular the learning of design skills by novices, in this case students taking their first computing courses in an Engineering school. The development of software designskills in novices has been a vexing topic for many years. Early interest was sparked in the 1970s (e.g. Dijkstra (1972) and Wirth (1976)) with the advent of a structured approach to programming. This was followed by attempts to devise programming languages to support or complement the structured approach (eg Pascal). Other approaches developed at this time have also contributed to the support ofprogramming tasks and in developing design skills. More recently the evolution of programming languages (eg C, Visual Basic and Ada) towards O-O principles and the creation of Java are having a major impact on software design. However, although O-O principles have clear advantages when applied to the higher level architectural aspects of program design, they still build on computationalprinciples (sequence, iteration, selection and recursion) that exist in, and are essential to, all programming languages. The understanding of these basic principles is challenging for the novice software designer. The key problem areas can be summarised as: • difficulties in conceptualising the computational task and its solution, starting from an informal description of the design problem • confusionbetween (programming) language syntax and the computational process • difficulties in devising and understanding the required algorithm

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• lack of ability (skill, experience) to understand the flow of computation within a program • difficulties in using, and appreciating the advantages of, appropriate encapsulation and modularisation concepts, and • a general lack of...