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DendralDendralExpert System
:: Topic to Present :::: Topic to Present ::
Presented by
Junaid Khan
University of Peshawar
Pakistan
Junaid_upesh@yahoo.com
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Dendral was an influential pioneer project inartificial intelligence (AI) of the 1960s, and thecomputer software expert system that it
produced. The name Dendral is a portmanteaux of the term
"Dendritic Algorithm"
Its primary aim was to help organic chemists in
identifying unknown organic molecules, byanalyzing their mass spectra and usingknowledge of chemistry.
What is Dendral???What is Dendral???
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It was done at Stanford University by Edward
Feigenbaum, Bruce Buchanan, Joshua Lederberg (a(a
Nobel prize winner in genetics)Nobel prize winner in genetics), and Carl D jerassi. It
began in 1965 and spans approximately half the history
of AI research.
Inventors:Inventors:
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It was written in Lisp (programming
language), which was considered the
language of AI. ± (jhon McCarthy, 1958, MIT)
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It was basically developed at stanford for NASAto perform chemical analysis of Martian soil for space missions.
There was no scientific algorithm for mappingThere was no scientific algorithm for mappingthe mass spectrum into its molecular structure.the mass spectrum into its molecular structure.Feigenbaum¶s job was to incorporate theFeigenbaum¶s job was to incorporate the
expertise of Lederberg into a computer programexpertise of Lederberg into a computer programto make it perform at a human expert level.to make it perform at a human expert level.Such programs were later calledSuch programs were later called expert expert systemssystems..
History«
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Continued«.
For this in laboratory, the ³generate and test´
method was used;
± (possible hypothesis about molecular structure are
generated and tested by matching to actual data).
There was an early realization that experts use
certain heuristics to rule out certain options with
possible structures.
It seemed like a good idea to encode that
knowledge in a software system.
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The software program
Dendral is considered thefirst expert system because it automated the
decision-making process and problem-solving
behavior of organic chemists.
DENDR AL marked a major ³paradigm shift´ inDENDR AL marked a major ³paradigm shift´ in
AI: a shift from general AI: a shift from general--purpose, knowledgepurpose, knowledge--
sparse weak methods to domainsparse weak methods to domain--specific,specific,
knowledgeknowledge--intensive techniquesintensive techniques..
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The aim of the project was to develop aThe aim of the project was to develop acomputer program to attain the level of computer program to attain the level of
performance of an experienced human chemist.performance of an experienced human chemist.
The DENDR AL project originated theThe DENDR AL project originated the
fundamental idea of expert systemsfundamental idea of expert systems ± ±
knowl edge engi neeri ng knowl edge engi neeri ng , which encompassed, which encompassed
techniques of capturing, analysing andtechniques of capturing, analysing and
expressing in rules an expert¶s ³knowexpressing in rules an expert¶s ³know--how´.how´.
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Dendral«.
It consists of two sub-programs
Heuristic Dendral
Meta-Dendral.
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Heuristic
Dendral is a program that uses massspectra or other experimental data together with
knowledge base of chemistry, to produce a set
of possible chemical structures that may be
responsible for producing the data. A mass spectrum of a compound is produced
by a mass spectrometer, and is used to deterime
its molecular weight, the sum of the masses of
its atomic constituents. ± (Example on Board)(H2O)
Heuristic Dendral
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Heuristic Dendral would use this input mass and the
knowledge of atomic mass numbers and valence rules,
to determine the possible combinations of atomic
constituents whose mass would add up to 18.
As the weight increases and the molecules become
more complex, the number of possible compounds
increases drastically. Thus, a program that is able to
reduce this number of candidate solutions through the
process of hypothesis formation is essential.
Heuristic Dendral
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Using heuristics in the form of highUsing heuristics in the form of high--qualityquality
specific rules, rulesspecific rules, rules--of of--thumb , thethumb , the
DENDR AL team proved that computersDENDR AL team proved that computers
could equal an expert in narrow, wellcould equal an expert in narrow, well
defined, problem areasdefined, problem areas..
Heuristic Dendral
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Meta-Dendral is a knowledge acquisition system that
receives the set of possible chemical structures and
corresponding mass spectra as input, and proposes a
set of hypotheses to explain correlation between some of
the proposed structures and the mass spectrum. These
hypotheses would be fed back to Heuristic Dendral totest their applicability.
Thus, "Heuristic Dendral is a performance system and
Meta-D
endral is a learning system". The program isbased on two important features: the plan-generate-test
paradigm and knowledge engineering.
META-Dendral
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³Derived systems´
Many systems were derived from Dendral,
including
MYCIN,
MOLGEN,
MACSYMA,
PROSPECTOR, XCON, and STEAMER.
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Any Any
Questions??Questions??
??
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³MESSAGE´³MESSAGE´
³If you take a heuristic conclusion as certain,
you may be fooled and disappointed; but if you
neglect heuristic conclusions altogether you
will make no progress at all."
::Herbert Simon::
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Hope you enjoyed!!!Hope you enjoyed!!!
Thank you!!!Thank you!!!