This is the eighth of nine sections :
1. Introduction
2. The cognitive processing element.
3. Ways of meeting the cognitive needs
4. Sequencers and the contextual overview in working storage.
5. Working storage : updating, and capacity.
6. Choosing how to meet the cognitive needs, and the implications for mental workload.
7. Learning and modes of processing.

Lisanne Bainbridge

This Section will focus on two main issues :
* the types of knowledge which a process operator has, and which therefore need to be represented,
* some (incomplete) suggestions for the nature of the underlying mechanisms which might be required.

8.1. Knowledge used in industrial process operation

The knowledge, about the environment and devices they are working with, which is used by process operators is a complex interplay of kinds and levels of detail.

8.1.1. Types of Knowledge.

I have found it useful (Bainbridge, 1988) to distinguish between the operators' knowledge of their own activities, in particular their working methods as described in this paper, and their knowledge of the environment and devices they are working with. However, it is possible to question this distinction. Evidently, something about processing having been done is conserved in some way, so that later processing on the same topic can be more effective. But it is not clear whether what is conserved is in the form of processing instructions or is a passive store of the results of processing. Bartlett (1954) and Neisser (1967) argue that remembering is a process, rather than simply a matter of accessing stored data.

A process operator does need to know at least about : the physical structure of the environment and devices, their positions, functions, and causal relations, and their behaviour and how to influence this behaviour (Bainbridge, 1988, 1993b). It may be easier in the abstract, when discussing these types of knowledge and representing them visually, to use a different type of diagram for each type of knowledge. But actually the process operators' mental representation must include the links from one type of knowledge to another, e.g. how physical positions affect causal relations which affect behaviour (given of course that the operator actually knows them). Figure 8.1.1 gives a small example of possible links between knowledge about physical structure, cause-effect relations, and the person's working method.

Figure 8.1.1 : Some of the links in the knowledge structure about a small part of a complex process (thick line = cause-effect relation). (This is adapted from a process control example in Bainbridge, 1991, Figure 3.)


8.1.2. Degrees of generality.

Section 3, part 3.1.2 suggested that the reference knowledge used by an experienced person is specifically organised to be compatible with the processing which accesses it. On the other hand, Section 7, part 7.2 above suggested that when people develop a new working method, as they seek relevant knowledge to use they may search through knowledge which is further and further removed from closeness to the particular problem. For an industrial process operator it is possible to suggest several degrees of distance of knowledge from their particular industrial process (Bainbridge, 1993b) :

1. Knowledge specifically referred to by an established working method (example in Figure 3.1.2). More detail about this is given below, in Section 8.2.1.

2. This direct reference knowledge may be underpinned by plant specific explanatory knowledge, such as the physical, causal and functional structure of the plant, mental models of plant behaviour in particular states, general sequences of events, or specific case stories.

3. This plant specific explanatory knowledge could be supported by industry specific knowledge. This could be engineering knowledge, for example what type of plant design is needed to make a particular chemical. Or it could be case stories. For example, operators in many chemical and nuclear plants exchange stories about unusual events in other plant.

4. This industry specific knowledge could be supported by general engineering explanatory knowledge, such as mental models of various categories of physical, functional and causal structures (e.g. general types of pumps, heat exchangers, cooling systems), and their behaviour or general scenarios.

5. This general engineering knowledge could be supported by general physical and chemical explanatory knowledge, such as about nuclear reactions or physical laws.

Items grouped together in this list are not necessarily all at the same distance from relevance to operating a plant. For example, some aspects of theoretical physics or chemistry may explain how the plant fundamentally works but may not be much use in operating it. But on the other hand, knowing the law relating pressure and volume might be directly relevant when thinking about an operating problem.

8.2. Aspects of the implications for mechanisms

Two of the many possible more speculative issues which are suggested by the nature of knowledge will be mentioned here : the possible modularity of working methods ('routines'), and the more fundamental constituents from which an element might be constructed.

8.2.1. Modularity of 'routines'

For each of the main cognitive needs, and the 'routines' for meeting them, which a process operator uses (see Section 3, part 3.2.3), it is possible to infer what knowledge is required in order to meet this need. Table 8.2 lists these inferences. Although this table shows inferences, rather than being based directly on data, some interesting points emerge. In particular, the knowledge bases appear to fall into two groups, those referred to by several of the main cognitive needs, and those which are referred by the processing ('routine') for only one of the main cognitive needs (Bainbridge, 1992).

Cognitive need	Knowledge referred to
identify	stimulus : identity. stimulus : hypotheses about identity, with test information. state : response required. operating procedures.
infer/ review present state	symptom : hypotheses about cause, with test information. dynamic models. scenarios.
review/ predict events	scenarios.
predict state	dynamic models.
review/ predict task goals	product targets. plant constraints.
evaluate state	product targets. plant constraints.
review action availability and effects	action : effect. dynamic models.
choose best action	effect required : actions with this effect. criteria for choice. operating procedures.
identify need for enabling action	action : required preconditions.
plan future activities	criteria for optimise/ compromise.

Table 8.2 : The knowledge referred to in meeting each of the main cognitive needs (adapted from Bainbridge, 1992, Table 4 ).(16K)
(a : b = a associated with b)


Knowledge bases accessed by several of the cognitive needs.
There are four groups of knowledge which are referred to for several purposes :
* dynamic models of the plant,
* scenarios of events,
* product targets and plant constraints, i.e. the criteria to which the operator is working,
* operating procedures, the formally defined overt working methods.
These types of knowledge tend to be taught in the more formal and verbal off-the-job training of operators.

Knowledge bases used during only one aspect of processing.
The following types of knowledge pairings are each used by only one main cognitive need, i.e. main 'routine'.

stimulus	identity, or hypothesis about identity
symptom	underlying cause, or hypothesis
state	response required
effect required	actions with this effect
action	effect
action	required preconditions

In each of these cases, the knowledge is of specific associations (e.g. this particular pattern on the interface means that is happening on the plant), not of general principles which could generate this answer. In many cases an operator can only acquire this type of associative knowledge by direct experience of operating the process.

It is interesting that each of the associative types of knowledge is used by only one of the main cognitive needs. If a particular group of if-then associations are specific to a particular main 'routine', this could support the notion that the main 'routines' are independent modules of processing. They appear to be independent, in the sense that processing within them is self-sufficient, in at least two ways :
* the working storage they contain is only available to processing within this 'routine' (Section 5, part 5.3).
* they may refer to a knowledge base which is used only by this 'routine'.

The three interdependent networks in a 'routine' (discussed in Section 3, part 3.2.1), i.e. the linked elements, the cross references in working storage, and the references to compatible knowledge, could give a strong and stable organisation which is difficult to disrupt. This might also provide an explanation for perceptual set.

8.2.2. More fundamental constituents

Several types of knowledge constituent appear to recur, to be used as basic building blocks in both the processing element and in knowledge representations, e.g. Figure 8.1.1. These are constituents such as : associations, attribute-value descriptors (e.g. the meta-knowledge for the 'routines'), conditionals, part-whole groupings of items (e.g. processing elements linked together to make a 'routine'),and is-a category groupings of items (e.g. grouping together working methods with similar outcomes). Both part-whole and category forms of item grouping can occur in several versions, see Bainbridge (1993a).

This could suggest that, however many types of cognitive element there might be, for processing and for knowledge representation, they are all different configurations built up from the same more fundamental constituents. To sort this out properly, it would be necessary to identify all the possible types of part-whole and category relation, and to check whether they could all occur both in processing and in knowledge representation.

If there are these more fundamental constituents, then cognitive processing might be organised in at least four levels, each with different properties :
* the basic constituents of any type of cognitive element,
* the processing elements,
* 'routines' consisting of elements. These 'routines' meet the cognitive needs, and have associated meta-knowledge about their properties, as well as local working storage and knowledge,
* 'sequencers' consisting mainly of conditional elements. These sequence the main cognitive needs, and maintain the overview which provides the context for decisions about what to do and how to do it.
This paper has suggested that both 'routines' and 'sequencers' might be emergent properties of the cognitive processing element.

Summary of main points in Section 8

* Process operators need knowledge about many different aspects of the environment, for example physical and causal knowledge, and the links between these different aspects. The knowledge used in devising new working methods, or for explanation, may be at several degrees of distance from direct relevance in operating the plant.
* Some types of associative knowledge may be specific to a particular cognitive need.
* 'Routines' might be independent processing modules, as they contain local working storage, and refer to unique knowledge.
* Knowledge stores might be constructed from a few basic types of element.
* Different types of cognitive element might be different configurations of the same more fundamental constituents, such as attribute-value descriptors, conditionals, part-whole groupings, and category groupings.
* Behaviour may be organised in at least four levels, each with different properties : constituents, elements, 'routines' and 'sequencers'.

©1998 Lisanne Bainbridge