Requirem ents for the evolution of a Cognitive Engineering discipline have been discussed. Those requirem ents arise in the presum ed disciplinary m atrix of Cognitive Engineering and include establishing a conception and exemplars. A conception is a technical expression of the ontology of the discipline (1.4). Since the ontology of Cognitive Engineering is understood to consist of cognitive design problem s, the conception is required to articulate a general form for this class of problem; it m ust be a technical expression of the general Cognitive Engineering design problem. Such a conception is proposed in this chapter^.
2.1 O rigin and locus of the problem
W hen a w orker interacts w ith an inform ation technology (a com puter, for convenience) to perform work, we can describe the w orker and com puter as a system em bedded in a 'dom ain' (Simon, 1969; Checkland, 1981). The goals of this '(interactive) w orksystem ' arise in the dom ain; the activities of the w orksystem seek to achieve those goals. The w orksystem adapts to its dom ain and, if it is well adapted, it will achieve its goals (Lewin, 1932; Simon, 1969; Shaw and Branford, 1977; Vicente, 1990).
^ The conception has been developed w ith John Long and earlier versions published (see Dowell and Long, 1988a,b, 1989). This chapter is a re-expression of its published form with additional explanations provided, its scope reduced, and its concepts given a limited revision.
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A pparent is a basic factoring of design concerns betw een those relating to the w orksystem and those relating to the domain. This factoring offers potentially significant advantages (Simon, 1969). First, it allows the sim plification of descriptions of w orksystem s w hich otherw ise m ight appear too complex for reasoning about. It m ay be possible to analyse or synthesise a w orksystem from requirem ents deriving from its purpose in the context of its dom ain, w ith only m inim al assum ptions about the inner environm ent of the worksystem . Simon (1969) even suggests: "Man view ed as a behaving system is quite simple. The complexity of his behaviour over tim e is largely a reflection of the complexity of the environm ent in w hich he finds himself." Second, the factoring m ay allow an economical dom ain description. In other w ords, the w orld needs only to be reasoned about to the extent th at its features form the object of intent of the worksystem : .". in very m any cases, w hether a system will achieve a particular goal depends on only a few characteristics of the outer environm ent" (Simon, 1969). A th ird basic advantage of the factoring is that because often quite different w orksystem s m ight achieve identical or sim ilar goals in a given dom ain (they are said to be functionally equivalent), a separate dom ain description helps reasoning about alternative designs.
To this point, design can be said to concern providing a w orksystem for a given dom ain to achieve specified goals. This m ost basic description makes plain, as it must^, the criteria for a successful design, viz: any worksystem w hich does achieve the specified goals in the given dom ain counts as an acceptable solution. Yet w orksystem s comm only operate in dom ains w here there are m ultiple and conflicting goals, and even w here all goals cannot be achieved. Moreover, the resources em ployed by the w orksystem in
achieving its goals m ust be considered. The concept of 'performance' expresses both the degree of goal achievem ent by the worksystem , and the cost of w orksystem resources used. So, m ore accurately, design m ight be said to concern providing for a given dom ain, a w orksystem having a desirable perform ance.
^ Checkland (1981) suggests that explicit problems must describe the conditions or criteria for their solution. Simon (1973) suggests that only well-structured problems describe such
criteria.
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We can represent these design concerns in terms of two related abstractions: the Cognitive Engineering design problem; and, the Software Engineering design problem. Each design problem expresses the general concern for providing a worksystem for a given dom ain having a desirable
performance. However the two problems differ in their scope. The
Cognitive Engineering design problem addresses the general concerns with regard to the worker, whilst the Software Engineering design problem addresses the general concerns w ith regard to the computer. Eigure 2.1 schematises those relationships.
Figure 2.1 The ontology of C ognitive Engineering.
The Cognitive Engineering
V
design problem The Software Engineering design problem Performance domain com puterSo, the origin and locus of the Cognitive Engineering design problem has been identified at a general level. To advance a conception of the Cognitive Engineering problem, a technical expression (1.4) of the worksystem and the domain is required.
2.2 The dom ain
The dom ain is a world in which work originates, is performed and has its consequences. It occurs in the intersection of organisations and technology. The domain is not 'the world' as consciously perceived and about which we may have common sense or physical theories; rather, it is an abstraction from that world. It is no more possible to point to some set of entities and
Chapter 2
A co n ception for C o g n itiv e E n g in eerin g
say "there is a domain", as it is to point to a w orker's activity and say "there is cognition." This section proposes concepts for expressing the dom ain and its relations w ith the worksystem.
1. Objects and their attributes. The dom ain is a w orld w hich consists of objects. Objects are expressed by, and so identified by, their attributes which can be abstract (e.g., information and knowledge) or physical (e.g., energy and m atter). Letters are objects; their abstract attributes support the com m unication of messages etc; their physical attributes support the v isu a l/v e rb a l representation of inform ation via language.
2. H ierarchy of complexity. The attributes of objects emerge at different levels w ithin a hierarchy of complexity. For example, characters and their configuration on a page are physical attributes of the object 'a letter' which em erge at one level of complexity; the message of the letter is an abstract attribute w hich emerges at a higher level of complexity.
A ttributes of objects are related in two ways w ithin the hierarchy of
complexity. First, attributes at different levels are related wherein those at one level are completely subsum ed in those at a higher level. In particular, abstract attributes will occur at higher levels of complexity than physical attributes and will subsum e those lower level physical attributes. For exam ple, the abstract attributes of an object 'message' concerning the representation of its content by language subsum e the lower level physical attributes, such as the font of the characters expressing the language. As an alternative example, an industrial process, such as a steel rolling process in a foundry, is a set of objects whose abstract attributes will include the
process's efficiency. Efficiency subsumes physical attributes of the process, - its pow er consum ption, rate of output, dim ensions of the o u tp u t (the rolled steel), etc - em erging at a lower level of complexity.
Second, attributes of objects are related w ithin levels of complexity. There is a dependency betw een the attributes of an object em erging w ithin the same level of complexity. For example, the attributes of the industrial process of pow er consum ption and rate of o utput emerge at the same level and are in ter-d ep en d en t.
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3. A ttribute states and affordance. Attributes of dom ain objects have states, an d some attributes may change state. For example, the content and
characters (attributes) of a letter (object) m ay change state: the content w ith respect to m eaning and gram m ar etc; its characters w ith respect to size and font etc. Because of the relations betw een attributes, state changes of one attribute m ay produce state changes in other attributes, w hether w ithin the sam e level of complexity, or across different levels of complexity. For exam ple, changing the rate of o u tp u t of an industrial process (lower level attribute) will change both its pow er consum ption (same level attribute) and its efficiency (higher level attribute).
Objects w hose attribute states have the potential to be changed are said to have an affordance for w ork (see Gibson, 1977). Affordance is generally pluralistic in the sense that there m ay be m any, or even, infinite
transform ations of an object, according to the potential changes of state of its attributes.
4. G oals. W ork is the intentional transform ation of objects having an affordance. For exam ple, com pleting a tax return' and 'w riting to an acquaintance', are each examples of work w here an object (i.e., a 'letter') is intentionally transform ed by state changes m ade in their attributes (i.e., their content, form at and status). Further editing of those letters w ould produce additional state changes.
The intention of w ork is to transform an object to a particular state, a state w hich can be described as a goal. Because attributes are related within the hierarchy of complexity, achieving a goal will generally entail state changes of m any attributes w ithin the hierarchy of complexity. The requirem ent of each attribute state change can be expressed as a goal. So for example, the goal d em anding transform ation of a letter m aking its m essage more courteous, w ould be expressed by a set of goals possibly requiring state changes of sem antic attributes of the propositional structure of the text, and of syntactic attributes of the grammatical structure. Hence, goals can be expressed w ithin a hierarchical structure describing the relations betw een goals, for exam ple, their sequences.
In the case of the com puter-controlled steel rolling process, the process is an object w hose intended transform ation is expressed by a goal. For example.
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the goal m ay specify the elim ination of deviations of the process from a desired efficiency. As indicated earlier, efficiency will at least subsume the process attributes of pow er consum ption, rate of output, dim ensions of the o u tp u t (the rolled steel), etc. State changes in rate of o u tput will be related to those in pow er consum ption and efficiency. In this way, the goal of
correcting deviations from the desired efficiency supposes the related goals of setting pow er consum ption, rate of output, dim ensions of the o u tput etc. Hence, the goals can be expressed as a goal structure.
Goals allow us to more precisely identify and differentiate betw een
dom ains. This greater precision is helpful because the same objects m ight be associated w ith different dom ains. For example, the object 'book' may be associated w ith the dom ain of typesetting (where goals express required state changes of the book's layout attributes) and w ith the dom ain of authorship (where goals express required changes of the book's textual content). M oreover, by defining the dom ain by reference to goals ensures that the dom ain is delim ited as the object of intent of the worksystem. This is vital to ensuring that the boundary of the dom ain can be identified:
entities are only seen to be included in the dom ain if a relationship w ith the goals can be established.
5. Q u ality . The desired transform ation of an object dem anded by goals will generally be of a multiplicity of attribute state changes - both w ithin and across levels of complexity. Consequently, there m ay be alternative
outcom es (transforms) which w ould satisfy the goals equally (letters w ith different styles, for example); here, each outcom e w ould represent a different com prom ise in attribute state changes of the object. By the same m easure, there m ay also be outcomes at variance w ith the goals. The concept of quality describes the variance of actual outcome w ith the goal.
This concept of quality brings us to a point w here the conception of the dom ain relates directly to the conception of the worksystem . Goals, as desired transform ations of dom ain objects, are reflected in the intentional behaviours of the worksystem , both w orker and com puter. The
achievem ent of those goals by the w orksystem is expressed as quality, a principal com ponent of system perform ance.
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2.3 The interactive w orksystem
Concepts of the interactive worksystem , and in particular of the worker, are p roposed in this section; the implications for the Cognitive Engineering design problem are discussed.
2.3.1 D efining the w orksystem
1. W orksystem b o u n d ary . W orkers are able to perform w ork and their behaviours are said to be intentional, or purposeful. Com puters, and m achines m ore generally, are designed to perform w ork and their behaviours are said to be intended, or purposiveh The worksystem is a system w hose boundary encloses all cognitive and com puter behaviours w hose purpose is to achieve goals in a given domain. For example, the behaviours of a w orker and control system m anaging a process constitute a w orksystem whose goal is to achieve a desired efficiency of the process. The w orksystem m ay achieve this goal, m odifying attribute states of the process, for example, by m odifying its input states. Critically, it is only by defining the dom ain th at the boundary of the worksystem can be established: w orkers m ay exhibit many contiguous behaviours, and only by specifying the dom ain of concern, m ight the boundary of the w orksystem enclosing all behaviours relevant to achieving the goals in the dom ain be correctly
identified^.
The concept of the w orksystem boundary is significant for the conception of the Cognitive Engineering design problem , because it delim its the scope of the problem to design concerns associated only w ith those aspects of the w orker and com puter seen to be included w ithin the boundary.
2. Goal assignm ent. The w orker and com puter are constituted w ithin the w orksystem by the definition of the common goals they address. Those
^ This appears consistent w ith Searle's argument that mental states but not programs have intentionality (Searle, 1980).
^ McShane, Dockrell and W ells (1992) point out that the computational theory of mind underlying C ognitive Science does not itself address the issue of "how it is that the symbols m anipulated com putationally have m eaning external to them selves, that is h ow they are grounded in terms of the objects and events of the everyday world." Bounding the worksystem w ith respect to the dom ain is an attempt to address this issue.
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goals can be decom posed, and in the decom position, subsidiary goals
assigned to either the w orker or the com puter. For example, replacem ent of a m is-spelled w ord required in a docum ent is a goal which can be expressed as a set of goals of necessary and related attribute state changes. In particular, the text field for the correctly spelled w ord dem ands an attribute state
change in the text spacing of the docum ent. Specifying that state change may be a goal assigned to the worker, as in the case of early wordprocessors, or it m ay be a goal assigned to the com puter, as in the 'w rap-round' behaviours of m o dern w ordprocessors.
The differential assignm ent of goals is significant for the conception of the C ognitive Engineering design problem because that assignm ent
differentiates design decisions concerning the w orker and com puter, respectively.
3. W orksystem behaviours and structures. The w orksystem is characterised th ro u g h the related concepts of structure and behaviour. The distinction betw een these concepts is m ost easily recognised by considering the 'functional equivalence' of different w orksystem s (2.1). Functionally
equivalent w orksystem s are systems w hich express the sam e behaviour and are therefore able to perform the same w ork and achieve the same goals in a given dom ain (Simon, 1969; Cum mins, 1983). Behaviours are abstract and physical. A bstract behaviours are generally the acquisition, storage,
transform ation and com m unication of inform ation. They represent and process inform ation concerning; dom ain objects and their attributes, attribute relations and attribute states, and goals. Physical behaviours express abstract behaviours through action.
If tw o w orksystem s having the same behaviour are functionally equivalent, the question arises as to w hat is different about those two worksystems? The difference lies in their respective structures^ ,2. The structures of the
w orksystem are the invariant^ architecture, both abstract (i.e., mental and
^ Sim on describes functionally equivalent system s as having the same behaviours but p ossessing different "mechanisms" (Simon, 1969, pg 148).
2 The distinction between behaviour <ind structure can be recognised in much of the discourse