44129679 Dendral Expert System

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DendralDendralExpert System

:: Topic to Present :::: Topic to Present ::

Presented by

Junaid Khan

University of Peshawar

Pakistan

[email protected]



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???



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:



It was written in Lisp (programming

language), which was considered the

language of AI. ± (jhon McCarthy, 1958, MIT)



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«



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.





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..



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´.



Dendral«.

It consists of two sub-programs

Heuristic Dendral

Meta-Dendral.



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



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



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



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



³Derived systems´

Many systems were derived from Dendral,

including

MYCIN,

MOLGEN,

MACSYMA,

PROSPECTOR, XCON, and STEAMER.



Any Any

Questions??Questions??

??



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::



Hope you enjoyed!!!Hope you enjoyed!!!

Thank you!!!Thank you!!!

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44129679 Dendral Expert System

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