
 
theoretical framework for building expert systems in 
psychiatry, and for future research.  
We believe medical expert system development 
in general faces a number of challenges in relation to 
the domains of conceptual modelling, 
implementation, and social and organisational 
aspects. The main problems of the previous 
approaches(e.g. INTERNIS-1/ CADUCEUS 
(Wolfram, 1995); (Miller, 1984); CADIAG-1 and 
CADIAG-2 (Adlassnig and Kolarzs, 1986); 
Parsimonious Covering Theory (Reggia and Peng, 
1987); A Process Model of Diagnostic Reasoning 
(Stausberg and Person, 1999) to development of 
medical expert systems include: failure to develop 
conceptual models that capture the depth of the 
domain; difficulties in developing a sufficiently 
large knowledgebase; and failure to take into 
consideration the social and organisational issues 
related to operational aspects of the implemented 
system. The authors have discussed these aspects in 
a separate paper (including the limitations of the 
previous approaches), and have proposed a 
development framework in order to overcome these 
challenges (Fernando et al., 2011). The very first 
step towards developing a successful medical expert 
system is developing a conceptual model that 
captures the depth and the complexity of clinical 
reasoning in specialised medical domains. This 
paper and the previous one attempt to achieve this 
first step, specifically in the field of psychiatry. 
2 KNOWLEDGEBASE MODEL 
The key to successful clinical inference is the 
structure of the knowledgebase. Whilst there are 
approaches in which the knowledgebase is 
independent from the inference process (e.g. 
CLASSIKA (Gappa et al., 1993), PROTÉGÉ (Tu et 
al., 1995), such approaches are deemed unsuitable 
for a highly specialised knowledge domain such as 
psychiatry, in which the inference mechanism is 
dependent on the knowledgebase structure from the 
clinician’s perspective. 
The knowledgebase encompasses three domains: 
diagnostic knowledge; etiological knowledge; and 
the treatment knowledge, which may be organized 
as a hierarchy as described in Figure-1. The 
diagnostic domain of the knowledgebase consists of 
layers representing respectively individual 
symptoms, and clinical phenomena, in which 
symptoms combine to form unique clinical 
phenomena. The etiological domain of the 
knowledgebase consists of layers representing 
respectively model concepts, and explanatory 
models, which can be derived from a number of 
etiological theories in psychiatry including ego-
psychology (Freud 1923); self-psychology (Kohut, 
2009); object-relations theory (Ogden, 1983); 
attachment theory (Bowlby, 1969); cognitive 
schema therapy model (Young et al., 2003); and 
Interpersonal Therapy Model (Weissman et al., 
2000). Each explanatory model consists of a unique 
combination of model concepts. Each clinical 
phenomenon is related to one or more model 
concepts, thus bridging the diagnostic domain and 
the etiological domain of the knowledgebase. The 
treatment domain consists of layers representing 
respectively treatment components, and individual 
treatments. Each treatment comprises a unique 
combination of treatment components. Figure-2 
explains the knowledgebase model using an 
example, in which the two symptoms “low self-
confidence” and “oversensitivity to criticism” along 
with several other symptoms form the clinical 
phenomenon “Low self-esteem”. Next, this clinical 
phenomenon is related to the model concept, 
“Cognitive schema of defective self” in the 
etiological knowledge domain. One explanatory 
model is shown in the next layer of the etiological 
knowledgebase, and it is made up of three model 
concepts: “Predisposing events”, “Cognitive schema 
of defective self” and “Precipitating events”. This 
explanatory model is related to the treatment 
component “Cognitive Re-structuring” in the 
treatment knowledge domain, which happens to be a 
part of the treatment “Cognitive Behaviour 
Therapy”. The clinical basis of this structure of the 
knowledgebase is not within the scope of this paper 
and is covered elsewhere (Fernando et al., 2011). 
Clinical phenomena are made up of a 
constellation of symptoms, and arguably play a more 
critical role in clinical reasoning in psychiatry 
compared to other branches of medicine. They are 
directly related to phenomenological concepts in 
psychiatry, and can be considered as core clinical 
features or recurrent themes in clinical scenarios. 
Diagnostic inference based on clinical phenomena is 
considered to have more reliability and validity 
compared to that based on symptoms, since each 
clinical phenomenon is a unique constellation of a 
number of clinical symptoms. 
The main components of the diagnostic 
knowledgebase and their relations are defined as 
follows. 
={
,
,…,
} is the set of all symptoms. 
ℎ={
,
,…,
} is the set of all clinical 
phenomena. 
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