Knowledge Creation and Retrieval in Program Design: A Comparison of Novice and intermediate Student Programmers

Abstract

Program design, from initial idea to executable code, was studied in a group of novice (first programming course) and a group of intermediate (second course) student programmers. The approach of the intermediate students could usually be described as forward and top-down design, but the behavior of the novices could not be so easily captured.Top-down design depends on both the expertise of the programmer and the difficulty of the problem. When faced with a difficult problem, even the expert has to build up a solution from simple pieces. In the approach adopted here, top-down design is based on the refinement of a known solution or schema that is retrieved and expanded at progressively greater levels of detail. If the expert knows all the required abstract and detailed schemas, then the design shows a pattern of top-down and forward expansion at all levels. When a schema cannot be retrieved and has to be created, top-down design breaks down and is replaced by bottom-up design. At the extreme, a rank novice has to create all the required plans, and design then shows consistent bottom-up and backward solution development.Separating plan retrieval from plan creation has three important conse-

A Review of Australasian Investigations into Problem Solving and the Novice Programmer

“…For example, experts and novices can be distinguished by how they undertake comprehension (Brooks, 1983) or generation (Rist, 1995). During program generation an expert can rely on a tacit body of programming plans developed through solving past problems (Soloway, 1986) while a novice has traditionally been expected to conceive and apply plans, with varying degrees of success (Rist, 1991). The distinction of expertise by use of strategy is suggested by Bailie (1991, p. 277): "one feature clearly distinguishing the novice from the expert programmer is the ability to plan."…”

“…Johnson (1986) gave a description of the inner workings of PROUST and also, for perhaps the first time, released a catalogue of goals and related plans. During the 1990s investigations by Australian researcher Rist (1991;1995) revealed how novices expound and apply plans. But in general, the idea of the schema/plan was not used by instructors, until the rise of the object paradigm, which brought with it a new sense of reuse and a new term to computing: patterns.…”

Program structure and design

“…Code is often added to a program one plan chunk at a time (Detienne, 1995;Rist, 1990Rist, , 1991. Novices are forced to do this because they code each line as soon as it is designed, so the actions in the plan appear one at a time, backward from the goal.…”

“…Novices are forced to do this because they code each line as soon as it is designed, so the actions in the plan appear one at a time, backward from the goal. Experts can retrieve a complete plan schema as a single chunk, or plan a solution mentally before writing any code; in these cases, the code appears in linear order from the first to the last action (Davies, 1991;Rist, 1989Rist, , 1991. For languages in which the plan structure is clear, such as Pascal, code tends to be added in plan chunks.…”

“…If code is written when the concrete structure is generated, then the observable behaviour this strategy generates is overall forward coding in plan chunks, but backward coding within a chunk: Design is forward globally, but "everywhere backward locally !" If a schema is retrieved, then it can be coded forward through the stored linear structure, and design will be generally forward with some chunks showing forward and some backward in generation order; this was the pattern of coding reported in Rist (1989Rist ( ), 1991.…”