• Expert systems uses expert knowledge.
• Expert knowledge is not limited to books.
• It can also be privileged knowledge known only to
highly trained and experienced experts in a field.
• Such knowledge is primarily intuitive.
• Decisions are based on situation, judgement and
experience and it has a high probability of being
• Computerized systems can be used as a database
of experts decisions especially in engineering
Database of Information
Rule Based Programming
Justify its Reasoning
• Rule based programming means the use of
IF/THEN algorithmic structures to codify
the decision rules from the expert.
• Engineers can be used to develop expert
systems by using their expertise.
Areas of expertise of Expert Systems
• Engineering modeling
• Taxonomy and morphology
• Manufacturing methods
• Optimization Criteria
• Engineers learns the laws of nature and procedures
• Synthesis is the art of putting together a new
machine, structure, chemical process, electrical
circuit, or system.
• It is designer’s unique contribution to the art of
engineering and the basis of industrial civilization.
• Duplicating synthesis in an expert system is far
beyond our present knowledge of human thinking.
• Analysis is an essential component of design.
• It ensures that the design is feasible and will meet the
• Analysis can also be used to examine that the design is
feasible in a optimum way.
– Build engineering model of the physical model.
– Decide on the important failure modes.
• Will a roof beam fail from excessive yielding of the material, or
collapse by buckling, or shearing of the end fasteners ?
• What level of snow loading should be applied ?
• Will a highway carry enough vehicles, have an adequate life, be safe,
convenient, not require excessive maintenance, and permit snow
removal under extreme conditions ?
• Will an aircraft design have adequate life, reliability,
capacity, controllability, and so on ?
• Will a transmission line carry the required current; or
will an electrical motor provide the required power ?
• It requires engineering skill, experience,
intuition and judgement for such predictions.
• Modeling of uncertainty is a major element of
decision making for modeling.
• Poor judgement implies poor models.
Taxonomy and Morphology
• Engineering expertise is needed about the physical
• New designs usually imply new combinations of
• Advent of new element may not produce better designs
than existing ones.
– Proper knowledge about materials is a must.
• What is the best steel for both strength and corrosion resistance ?
• What is the best lubricant for long life, minimum noise, minimum
friction loss, and minimum maintenance ?
• Engineer must also be an expert on
manufacturing and building processes.
– How metal parts are formed, cut or cast ?
– How roads and buildings are constructed ?
– How microchips are produced, and so on.
• Maintenance - knowledge of maintenance
methods and testing procedures including special
skills in diagnostic procedures and use of sensors.
• Applications – expertise is also needed on the field
of application of the device or system being
• Tools – expertise on how to use the tools of the
trade (using computers, calculators, etc)
• Expertise on the criteria to select the best possible
• Engineers normally work with immediate criteria.
– Maximize or minimize the performance criteria.
• Minimum weight for an aircraft.
• Minimum cost of a lathe.
• Maximum capacity of a railway car, and so on.
• These can be achieved by analytical optimization or by
• Sometimes abstractions (deriving excitement, pleasure,
aesthetics, etc) can be objectives and they are usually
satisfied combining judgement and experience.
• Aesthetics :
– Ergonomics – human-machine interaction.
– Art of satisfying subtle human values.
• Risk judgement :
Examples : Super Expertise
• Why did you use ductile iron rather than steel for that part ?
– Ductile iron is cheaper than steel for a part that might be cast, and
it has excellent ductility for this service. Also it has worked well in
previous similar applications.
• Why did you not heat treat that steel to give a yield strength of 250,000
psi (172 MPa) instead of only 125,000 psi (86.2 MPa) ?
– I would like to have had the high yield strength that is possible with that
steel, but the ductility, impact strength, and resistance to crack growth are
too low at that hardness. So I had to sacrifice yield strength to achieve
them. The exact trade-off level that I chose is based on my experience in
this application – It is intuitive judgement.
• Why did you use three bearings instead of two, in order to support that
shaft in your gear box ?
– We have found in this kind of application that only two bearings results in
excessive shaft deflection with corresponding misalignment of the gear
teeth, and excessive wear and noise.
• Experts express their knowledge in the form
of rules for problem solving.
– IF the ‘traffic light’ is green
– THEN the action is go
– IF the ‘traffic light’ is red
– THEN the action is stop
Rules for knowledge representation
• Rule is an IF-THEN structure that relates the
information or facts in the IF part to some action
in the THEN part. A rule provides some
description of how to solve a problem.
• Any rule consist of two parts: the IF part, called
the antecedent (premise or condition) and the
THEN part called the consequent (conclusion or
• A rule can have multiple antecedents joined
by the keywords AND (conjunction), OR
(disjunction) or a combination of both.
– IF <antecedent 1> IF <antecedent 1>
AND <antecedent 2> OR <antecedent 2>
AND <antecedent n> OR <antecedent n>
THEN <consequent> THEN <consequent>
Rules can represent relations, recommendations,
directives, strategies and heuristics:
– IF the ‘fuel tank’ is empty
– THEN the car is dead
– IF the season is autumn
– AND the sky is cloudy
– AND the forecast is drizzle
– THEN the advice is ‘take an umbrella’
– IF the car is dead
– AND the ‘fuel tank’ is empty
– THEN the action is ‘refuel the tank’
– IF the car is dead
– THEN the action is ‘check the fuel tank
step 1 is complete
– IF the step 1 is complete
– AND the ‘fuel tank’ is full
– THEN the action is ‘check the battery’
step 2 is complete
– IF the spill is liquid
– AND the ‘spill pH’ < 6
– AND the ‘spill smell’ is vinegar
– THEN the ‘spill material’ is ‘acetic acid’
Development Team for Expert System
• Domain Expert
• Knowledge Engineer
• Project Manager
• Knowledge and skills for a specific domain.
• Expert has the greatest expertise in a given domain.
• His expertise is to be captured in the expert system.
• Expert should be able to communicate his or her knowledge, be
willing to participate in the expert system development and
commit a substantial amount of time to the project.
• The domain expert is the most important player in the
• Capable of designing, building and testing an expert system.
• He interviews the domain expert to find out how a particular
problem is solved.
• Finds out the reasoning methods the expert uses to handle facts
and rules and decides how to represent them in the expert
• Decides on development software/expert system shell.
• Testing, revising and integrating the expert system into the
• Responsible for actual programming of the
• Must be familiar with AI languages such as
LISP, PROLOG, etc and the application of
expert system shells.
• Must also know conventional programming
languages such as C, Pascal, Fortran and
• Project Manager is the leader and
coordinates the development of the expert
• End-user is the also called the user. Must
be comfortable with the expert system. The
inputs, outputs, etc.
LISP does not evaluate expressions as a sequence of
define x, a and b
y = ax + b
z = y*y + sin(y)
Instead the computer is presented with a function, which it
define x, a and b
(f2 (f1 x a b))
f1 and f2 are functions as follows.
f1 = (PLUS (TIMES a x) b)
f2 = (PLUS (TIMES f1 f1) (SIN f1))
Algebraic type expressions are not used
Functions are mostly operators that manipulate
Symbols can be used to represent physical
quantities or physical things and concepts.
(SETQ TOOLS (LIST : ‘HAMMER’,
‘SCREWDRIVER’, ‘SAW’, ‘WRENCH’)
Most widely used in artificial intelligence.
Started by Japanese.
Higher level language than others.
Specially designed for logic expressions