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Structuring information for design problem solving

CIP-DATA KONINKLUKE BffiLIOTHEEK, DEN HAAG Vries, Aline Erica de Structuring information for design problem solving I Aline Erica de Vries. - Eindhoven : Eindhoven University of Technology Thesis Eindhoven. - With ref. ISBN 90-386-0014-3 Subject headings: design problem solving I information structures.

Structuring inforn1ation for design problen1 solving

PROEFSCHRIFf

ter verkrijging van de graad van doctor aan de Technische Universiteit Eindhoven, op gezag van de Rector Magnificus, prof.dr. J.H. van Lint, voor een commissie aangewezen door het College van Dekanen in het openbaar te verdedigen op dinsdag 13 september 1994 om 14.00 uur door

Aline Erica de Vries geboren te Amstelveen

druk: wibro dissertatiedrukkerij, helmond.

Dit pioefschrift is goedgekeurd door de promotoren: prof.dr. J.M. Pieters prof.dr.ir. M.F.Th. Bax eo-promotor: dr. A.J.M. de Jong

Aan mijn ouders

Acknowledgements

A number of people supported me in accomplishing this thesis. I would like to express my gratitude to: Ton de Jong for his expert guidance throughout the project. Both his interest and his criticism acted as an incentive to proceed with more determination. Joost van Andet for support of all kinds and for coming up with the idea of exploiting new media to present social science information to designers. Prof. dr. D.W. Vaags for his confidence in my execution of this project. Unfortunately, he died in its early stages. Prof.dr. J .M. Pieters and prof.dr.ir. M.F.Th. Bax for their valuable comments which gave rise to reflection on both theoretical and practical issues. Wouter van Joolingen and Melanie Njoo for reviewing the manuscript and for mutually sharing the ups and downs in the completion of a thesis. Joost Burger, Manfred van Gurchom, Guido Minnes, Laura Ouwehand, and Saskia Tan for helping me to overcome the many practical problems of doing research and to Erica Dodd for correcting my English. My colleagues at the Department of Philosophy and Social Sciences for their encouragements and, in particular, to Peter Verkerk and Anneloes Meinders for being invaluable roommates. Members of the Eindhoven Students Dance Society Footloose for providing a social environment in which I could take my mind off my work. And to Pascal for being with me.

Erica de V ries, Eindhoven, July 1994

Contents

1. Introduction and overview . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Overview of the thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Design processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Design methodology . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Generic design . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1 The design problem solver . . . . . . . . . . . . . . . . 2.3.2 Characteristics of design problems . . . . . . . . . . 2.3.3 Design task environment . . . . . . . . . . . . . . . . . 2.3.4 Design processes . . . . . . . . . . . . . . . . . . . . . . 2.4 Architectural design problem solving . . . . . . . . . . . . . 2.4.1 Descriptions of the architectural design process . 2.4.2 Comparing descriptions . . . . . . . . . . . . . . . . . . 2.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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.. 7 .. 9 . 10 . 11 . 11 . 14 . 15 . 16 . 17 . 21 . 26

3. Supporting design problem solving . . . . . . . . . . . . . . . . . . . . . 3.1 Computer-aided design: support tools . . . . . . . 3.2 Design information systems . . . . . . . . . . . . . 3.2.1 An information gathering framework . . . 3.2.2 Hypertext systems for design . . . . . . . . 3.2.3 Examples of hypertext systems . . . . . . . 3.3 Structuring information in hypertext systems . 3.3 .1 Types of structures . . . . . . . . . . . . . . . 3.3.2 Types of questions . . . . . . . . . . . . . . . 3.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . .

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27 27 29 30 31 32 33 34 36 37

4. Exploring effects of structure and form . . . . . . . . . . . . . . . . . .

4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . 4.1.1 Network versus hierarchical structures . 4.1.2 The form of infonnation . . . . . . . . . . 4.1.3 The current study . . . . . . . . . . . . . . . 4.2 Method. . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 Subjects . . . . . . . . . . . . . . . . . . . . . . 4.2.2 Experimental set-up . . . . . . . . . . .. . . 4.2.3 The information system . . . . . . . . . . . 4.2.4 Procedure . . . . . . . . . . . • . . . . . . . . 4.2.5 Analysis of the data . . . . . . . . . . . . . 4.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.1 General system use . . . . . . . . . . . . . . 4.3.2 Navigational characteristics . . . . . . . . 4.3.3 Exploration and design proposal . . . . . 4.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . .

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39 40 40 42 44 44 44 45 48 48 51 51 52 53 55

S. Matching purpose and structure . . . . . . . . . . . . . . . . . . . . . . .

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5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.1 Constraints in the design problem space . . . . . . . . . 5.1.2 Browsing andsearching ................ : . . . . 5.1.3 Research questions and predictions . . . . . . . . . . . . . 5.2 Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.1 Subjects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.2 The experimental set-:UP . . . . . . . . . . . . . . . . . . . . 5.2.3 The information system . . . . . . . . . . . . . . . . . . . . . 5.2.4 Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.5 Analysis of the data .·. . . . . . . . . . . . . . . . . . . . . . 5.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.1 Pretest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.2 Browse criterion test . . . . . . . . . . . . . . . . . . . . . . . 5.3.3 Search criterion test . . . . . . . . . . . . . . . . . . . . . . . 5.3.4 Count criterion test . . . . . . . . . . . . . . . . . . . . . . . . 5.3.5 Evaluating each task on the appropriate criterion test 5.3.6 Exploration . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . 5.4 Conclusions and discussion . . . . . . . . . . . . . . . . . . . . . . .

59 59 61 62 64 65 65 66 67 69 72 72 75 77 79 80 82 83

6. Design phases and task-adapted abstraction hierarchies . . . . . .

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6.1 Introduction . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . . . 6.1.1 Abstraction levels in the design problem space . . . . . 6.1.2 Problem solving: Reasoning from purpose to function and form . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1.3 Approaches in the presentation of information . . . . . 6.1.4 Research questions and predictions . . . . . . . . . . . . . 6.2 Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.1 Subjects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.2 Experimental set-up . . . . . . . . . . . . . . . . . . . . . . . 6.2.3 The information system . . . . . . . . . . . . . . . . . . . . . 6.2.4 Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.5 Analysis of the data . . . . . . . . . . . . . . . . . . . . . . . 6.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.1 System use .............................. 6.3.2 The enlargement of the initial problem space . . . . . . 6.3.3 Argumentation and aspects of the design proposals . . 6.4 Conclusions and discussion . . . . . . . . . . . . . . . . . . . . . . .

85 86

7. General discussion

87 88 91 93 93 93 94 97 98 101 101 103 106 108 111

7.1 Main results 7 .1.1 The structure of information . . . . . . . . . . . . . . . . . . 7 .1.2 Information gathering during design problem solving 7.2 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 Theoretical implications . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 .1 Construction of a design problem space . . . . . . . . . . 7.3.2 Design problem solving with information ........ 7.4 Directions for hypertext research . . . . . . . . . . . . . . . . . . . 7.5 Practical implications . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5.1 Design methods .......................... 7 .5.2 Educational purposes ................ ~ . . . . . . 7.5 .3 Recommendations for design information systems . .

111 113 115 117 119 119 120 122 123 123 124 124

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Appendix A Experimental structures . . . . . . . . . . . . . . . . . . . . . . . Appendix B Classification scheme . . . . . . . . . . . . . . . . . . . . . . . . . Samenvatting (summary in Dutch) . . . . . . . . . . . . . . . . . . . . . . . . . Resume (summary in French) ............................ Curriculum vitae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

127 137 141 143 147 151

1 Introduction and overview

This chapter introduces the central theme of this thesis: information gathering through the use of information systems during design processes. The scope of the situation of interest is delineated, and main research questions formulated. The chapter ends with an overview of the thesis.

1.1 Introduction Almost everything that surrounds us is the result of a design process. However, objects were not always designed before they were made. For example, people initially made their own fireplace adapted to their own needs, and later, craftsmen constructed cooking areas from experience. Nowadays, cooking devices are first designed and then manufactured before entering our homes. In this thesis, design processes will be described from a cognitive psychological viewpoint. Designing as the creation of an external representation of something to be made has been recognised as a cognitive task (Goel & Pirolli, 1992; Simon, 1981). Moreover, the design process as a problem solving process has become a subject of study in cognitive psychology. The particular discipline studied in this thesis is architectural design, which is often considered the most typical example of design (Schon, 1983). The designer of an object needs information, for example technical information. However, the example above shows that another type of information is also required. Whereas people made fireplaces adapted to their

2

Chapter 1

own needs, such as grilling meat, a designer of modern cooking devices has to take into account needs of others, i.e. the future user who wants to eat quickly, or the gourmet who likes to prepare refined sauces. The separation between designer and user means that information is required on human behaviour in general, and about needs associated with the object to be designed specifically. In this thesis, information gathering during the design process is studied. Moreover, it deals with gathering information on human behaviour provided by social science research. Research in design-related areas causes a steady growth of the body of information of potential relevance to design problems. However, several researchers observed that existing scientific, technical, and social knowledge is mostly unexploited by architectural designers (van Andel, 1988; Goodey & Matthew, 1971; Hamel, 1990; Newland, Powell, & Creed, 1987; Powell, 1987). Three types of explanations have been raised for the lack of information access by designers. Van Andel (1988) interprets the phenomenon as a communication gap between researchers (writers of design information) and designers. Researchers and designers differ in a number of respects. For example, whereas researchers aim at an accumulation of knowledge, designers focus on finding a solution to one particular problem. A second type of explanation focuses mainly on the designers. Among the proponents are Newland, Powell, and Creed (1987) and Powell (1987), who suggest that designers have a reluctance to consult written data, 'and instead rely on personal experience. Designers in this view are thought to have selective strategies for acquiring information. The third type of explanation relates to the characteristics of the information and the way it is presented. There is a growing body of information and specialist experience, and this information is hard to handle, widespread, diffuse and unorganised (Alexander, 1964). Proponents of this view have made some recommendations to alleviate the problem, e.g., on the applicability, clarity, and the use of visual material in information for designers (Goodey & Matthew, 1971; Hamel, 1990). In this thesis, design information systems are put forward as a solution to the problem. Computers could serve as a storage medium for large quantities of design information. Advantages of using the computer for design information are mentioned for design disciplines in general (Pirolli & Russell, 1990). However, specifically in architecture, computers can offer possibilities of dealing with the increased complexity of design problems and the exponential proliferation of information of relevance to the design process (Goumain &

Introduction and overview

3

Sharit, 1988). Information systems already exist for storing and retrieving design information such as catalogues of components and building standards (Broadbent, 1988). Nevertheless, there is also a large quantity of more complex information which has to be made accessible to designers, such as the growing collection of research results from the social sciences mentioned above. New techniques in information technology, such as hypertext systems, permit alternative ways of storing and retrieving information. Hypertext systems, which are discussed in more detail in Chapter 3, were especially designed to allow a variation of possibilities of structuring and presenting information. These new techniques also raise questions regarding the influence of information structure, and the way in which information systems will be used in the context of a specific task. These considerations have led to the following general research questions central to this thesis: •

What is the influence of the structure of information in a design information system on design problem solving?

•

How can information gathering in a design information system during design problem solving be characterised?

To answer these questions, more theoretical background on two main topics has to be given. First, more insight is needed into the nature of design processes. Second, the idea of supporting design processes with the help of computers has to be elaborated upon. Literature regarding both topics will be reviewed in the next two chapters. Thereafter, the research questions will be addressed through three empirical studies. So far, three restrictions for the study in this thesis have been introduced. First, the study of design processes in this thesis is restricted to one particular discipline: architecture. Furthermore, the particular type of information given as input to the design process comes from research in the social sciences. Finally, the type of computer support that is studied focuses on presenting information with the help of information systems. In particular, presentation aspects such as the structure of information are tackled, and the use of such an information system during the design process is examined. One restriction can be added to this list: the choice of subjects in the experiments. The experiments in this thesis have been performed with a particular group of subjects, namely advanced (3rd year and higher) students in architecture.

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Chapter 1

Advanced students have acquired experience with solving design problems in design projects throughout their earlier years of study. They have comparable backgrounds, design experience and design knowledge, and thus form a relatively homogeneous group. The subjects that participated in the studies in this thesis can be considered intermediates in solving design problems. Systematic research comparing different levels of design expertise is scarce (Teyken, 1988), and studies often involve only a few subjects (see for example Foz, 1972; Rowland, 1992). Regarding information gathering during design problem solving, intermediates are situated between beginners showing limited information gathering, and experts showing extensive information gathering (Christiaans, 1992; Rowland, 1992). However, as mentioned in the beginning of this chapter, even the information gathering of expert designers is considered non-optimal, neglecting some types of information (see also Hamel, 1990).

1.2 Overview of the thesis This thesis comprises two main parts: a theoretical part (Chapters 2 and 3) and an empirical part (Chapters 4, 5, and 6). In Chapter 2, theories on design processes are reviewed from three viewpoints. First, practitioners, in design disciplines themselves, have something to say about the way in" which they operate. Second, there has been considerable theorising on design processes in cognitive psychology, as will be shown in a section on generic design. Third, design processes can also be described by focusing on descriptions in the particular discipline of interest in this thesis: architectural design. The three perspectives contribute to an integrated view of design processes, which forms the theoretical framework for the empirical studies. In Chapter 3, several ways of supporting the design process by using computers are examined. Computers can be employed for supporting regular design activities, for example drawing or calculating. This type of support is briefly reviewed before turning to the type of support studied in this thesis: informational support. Factors pertaining to the success of information systems such as situational characteristics, contents and type of system are discussed, keeping in mind a design setting. Some empirical research concerning the structure of information- and the use of information systems is reviewed. Chapter 4 presents a first exploratory study into the use of an information system during the design process. Students performed a design

Introduction and overview

5

task, and an information system was at their disposal for consultation during the design process. The influence of structure (network versus hierarchy) and form (text-only versus text and pictures) on the use of the information system and on the resulting design proposal was studied. The objective of Chapter 5 is to investigate interactions between the particular purpose for using an information system during the design process and the structure in which the information is presented. Following the suggestions of Bransford, Franks, Morris, and Stein (1979), performance measures were related to the desired outcome for each of the purposes included in the study. In Chapter 6, the view that two design phases can be distinguished is adopted: problem structuring and problem solving. This third empirical study introduces the notion of abstraction hierarchies in the presentation of information. After a discussion of the role of abstraction levels in design information and design problem solving, an experiment is described which tests three separate organisations according to abstraction level for use during the two main phases in the design process. Finally, Chapter 7 presents the main results of the studies in this thesis. Theoretical and practical implications of the results are addressed.

2 Design processes

The aim of this chapter is to give a characterisation of design processes. This is done by drawing on three sources: design methodology, cognitive psychology, and more specifically, psychological descriptions ofarchitectural design processes.

2.1 Introduction Design is concerned with formulating a plan representing some artefact that, once it is made, will fulfil certain needs. This characterisation of the design activity comprises three key elements frequently encountered in descriptions of design. The first element is the idea of formulating a plan or model of something before it is made. The development of the representation of the artefact precedes the making of the artefact itself (Archer, 1984; Habraken, 1988). The second element is that the artefact has to fulfil needs. There is a discrepancy between the current state and some desired state in the world, and designing is a goal-directed activity aimed at imagining an artefact that will change the situation (Archer, 1969; Simon, 1981). The third element is the activity of formulating or designing a representation of the artefact as opposed to calculating a solution. This element has to do with designing as a creative activity. Arriving at a solution by calculation is not regarded as designing (Archer, 1984). The process of design aims at attaining goals. The product of a design activity is the external representation of the artefact or some future state of

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Chapter 2

affairs (Goel & Pirolli, 1992). An artefact may be a material object such as a house or a hospital, but it may also be a spatial arrangement of elements in a situation, e.g., houses in a neighbourhood (Boekholt, 1984), or some series of steps to be taken, e.g., a social welfare policy (Simon, 1981). Designing is the essential process in a number of disciplines, such as urban planning, architecture, industrial design, engineering design, instructional design, and software design. Design theories were developed on the basis of experience in these design disciplines. Theories wen~ developed in order to clarify the nature of the process for design practice and education and they provide a methodology of design. The resulting models of the design process are often prescriptive. They prescribe the way in which a design ought to be arrived at, rather than the process as it takes place in reality. The first section of this chapter gives a brief description of normative theories of design as can be found in design methodology. Cognitive psychology provides another approach to the study of design processes. Cognitive psychological theories propose a valuable contribution to normative design theories for two reasons. First, they yield more in-depth knowledge on design processes. Second, since theories developed from a cognitive psychological perspective aim at a description of the process, considerable effort is directed at empirical validation. Within cognitive psychology, designing is generally seen as problem solving. Problem solving research has known a shift from the study of symbolic tasks, such as cryptarithmetic, logic and chess to the study of more complex real-world tasks. Design problems have been taken as an example of real-world problems that can be studied within Newell and Simon's theory of human problem solving (Newell & Simon, .1972). Section 2.3 concentrates on a psychological description of design processes. The third section centres around theories in the specific discipline studied in this thesis: architectural design. Three theories will be described in more detail. Two theories, Akin's (1986) and Hamel's (1990), represent the descriptive approach. But first, Boekholt's (1984) characterisation of the design process will be discussed as a representative of the more prescriptive approach. His theory, although from the architectural discipline, incorporates cognitive psychological notions. Nevertheless, Boekholt did not carry out empirical studies to validate his theory. Although prescriptive and descriptive design theories represent a different approach, the distinction is not rigorous. It is reasonable to assume a correspondence between the subjective, ideological view of designers and the objective general view of scientists

Design processes

9

(Thomas & Carroll, 1979). Therefore, both approaches are represented in Section 2.4.

2.2 Design methodology Whereas design processes have been described in specific fields, attempts have also been made to develop a design methodology independent of a specific field. In design methodology, the act of designing is seen as being independent of the specific discipline or the character of the specific artefact that is designed. The first conference on design methods took place in 1962 (Jones & Thornley, 1963) and is generally seen as the beginning of a design methodology. Design methodology aimed at seeking out and establishing systematic methods of problem solving in design. Systematic design methods were developed in response to the increasing complexity of design problems. The goal of systematic design was to reduce the amount of design error, redesign and delay, and to create room for more imaginative design (Jones, 1963). Three stages are commonly identified in the design process (e.g., in Jones, 1963; Lawson, 1990; Zeisel, 1984). These stages are: • • •

Analysis Synthesis Evaluation

Analysis is associated with an exploration and decomposition of the problem. Analysis also involves looking at available information, listing objectives and requirements, and identifying the interconnections among components of the problem. Synthesis is concerned with attempts to solve subproblems in isolation, and to combine them to form a complete design. During evaluation, the suggested solution or solutions should be judged to see whether they fulfil the requirements stated at the outset. A number of specific design methods are associated with each stage. Jones (1980) gives an extensive overview of methods that could be used in each of the three stages. During the analysis stage, methods aimed at exploring the design situation can be useful. Examples of such methods are stating objectives, literature searches and interview techniques. Methods of searching for ideas, such as brainstorming, can also be used in this stage. In the synthesis stage, methods of exploring interdependencies within the design

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Chapter 2

problem come into play. For example, interaction matrices and interaction nets permit the depiction of the interactions between different components of a design. Finally, methods of evaluation consist of checklists, selecting criteria and ranking and weighing. In most prescriptive theories, the order of analysis, synthesis, and evaluation is fixed. This is called a waterfall model because each phase must be finished before turning to the next, and once a phase is finished one cannot go back to that phase. However, most pres~riptive models of the design process tolerate going back to a former stage by providing return loops in their models (Jones, 1980; Lawson, 1990). In this view, analysis, synthesis, and evaluation activities appear throughout the design process, and it is their relative importance that is used in demarcating stages. In disciplines such as software design, the stages in the design process may be even more flexible and intertwined with the actual making of the artefact. For instance, in software design, development of a program can take place by rapid prototyping and making incremental improvements (de Hoog, de Jong, & de Vries, 1994). In most disciplines however, such a strategy would involve too many risks. Systematic design methods are developed and taught in order to avoid those risks associated with design errors (van den Kroonenberg & Siers, 1992; Roozenburg & Eekels, 1991).

2.3 Generic design In this section, attention is paid to design processes from a cognitive psychological perspective. Within cognitive psychology, efforts are directed towards a model that generalises across design tasks in different disciplines. This study is referred to as generic design, and is based on the idea that important similarities exist between different design disciplines on the one hand, whereas on the other hand there are significant differences between design disciplines and non-design disciplines (Goel & Pirolli, 1992). A prevailing framework for the psychological study of design is the information processing theory of human problem solving (Newell & Simon, 1972). The theory stresses the features of the structure of the information processing system (the problem solver) and the task environment in which problem solving takes place. However, if design problems are a special category of problems, a theory of generic design should also demonstrate the particular characteristics of these problems and describe the processes needed to solve them. Therefore, generic design should describe the nature of four aspects:

Design processes • • • •

The The The The

11

cognitive system, i.e., the design problem solver characteristics of design problems environment in which design problem solving takes place design processes themselves

The next four subsections deal with each of these aspects in more detail.

2.3.1

The design problem solver

The design problem solver can be viewed as a cognitive system, as proposed by Newell and Simon (1972) to model the human problem solver in general. The human problem solver is an information processing system. The characteristics of such an information processing system are the existence of a set of elements (symbols), relations between these elements (symbol structures), a memory capable of storing and retaining symbol structures (short-term and long-term), and a processor that consists of information processes that act upon symbol structures. The relation with the environment is assured by receptors and effectors. This general structure of the information processing system is the same across tasks and problem solvers. The basic information processes, such as encoding, manipulation, and recall of information are assumed to be essentially similar across tasks. Human information processing is also subject to a number of constraints, such as limitations of short-term memory, access times for external memory, and serial processing (Newell & Simon, 1972). A theory of generic design should take into account these possibilities and limitations of human information processing.

2.3.2

Characteristics of design problems

Design problems are complex problems. For a typical design problem, the solution has to meet a set of requirements, and interactions exist between these requirements (Alexander, 1964; Lawson, 1990). Another salient aspect of design problems is that there is no right or wrong solution but only better or worse solutions (Wade, 1977). Furthermore, requirements in a design problem often involve a variety of disciplines. The amount of information relevant in solving a design problem is large (Lawson, 1990). These features coincide with two main distinctions made in problem solving research in

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Chapter 2

general: problems are said to be more or less well-structured, and to involve more or less domain knowledge. These two distinctions applied to design problems characterise the latter specifically as being ill-structured and as involving a large body of domain knowledge (de Vries, 1990; Goel & Pirolli, 1992). Ill-structured problems The distinction between well-structured and ill-s~ructured problems is frequently mentioned in the literature. Ill-structured problems are defined as lacking some or all characteristics of well-structured problems (Simon, 1973). These characteristics are related to the contents of a problem space. The problem space is taken to be the fundamental organisation for all goaloriented symbolic activity (Laird, Newell, & Rosenbloom, 1987). The problem space of a well-structured problem contains representations of:

• • •

All possible states (initial state, intermediate states, goal state) All possible or considerable transitions between states All knowledge about the problem

For well-structured problems the number of states that may be reached or considered in the course of problem solving is limited and can be represented in the problem space. The same can be said about the number· of possible transitions from one state to another. Therefore, the problem space for a wellstructured problem (in principle) can be enumerated. However, design problems have been placed towards the ill-structured end of the continuum because there is no finite problem space in which all possible states and transitions between states can be represented. Furthermore, it is difficult to decide on the limits of relevant information. The difficulty of establishing the body of knowledge that might bear on· a design problem means that the problem space cannot be delineated. In addition, Simon (1973) lists three other chara 0), whereas the number of materialisation statements decreases. It should be noted that the pretest reports contained more materialisations, e.g., prototypic objects like sand play area, slide etc. These objects were named to a lesser extent in the postte~t. The opposite was true for abstract concepts. The number of abstract concepts increased as a result of using the system. The figure also shows that the large size increase in the browse - network condition is almost equally distributed over all three abstraction levels.

Matching purpose and structure

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Number of elements (postlest - pretest) 6 5 4 3 2

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1 0 -1 -2 -3

• Network

-4

o

Hierarchy

Ill

Mixed

-5

a

b

Browse

c

a

b Search

c

a

b

c

Count

Figure 5.2 Changes in the number of elements in the problem space as a function of structure, task and abstraction level (a=abstract concept, b=performance requirement, c = materialisation).

5.3.3

Search criterion test

The search criterion test tested the subjects' knowledge of specific topics. The subjects in the search condition are expected to answer more topics on the search criterion test (maximum is 12) because they specifically searched for information on these topics. In addition, they are expected to be able to tell more about each topic, resulting in a higher total search score. Table 5.4 shows the number of topics answered with at least one relevant statement, and the search score (total number of relevant statements over all topics) 1• Multivariate analysis of variance revealed a main effect of task (F(4, 160) 5.27, p