hageman@asgb.UUCP (George W. Hageman) (12/31/85)
The following is the documentation file for an inference engine
written in C. There will be three other submittals to net.souces
consisting of the source for a rule compiler, inference engine, and,
a weather prediction expert rule base including an animals expert.
Have fun....
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INFERENCE -- SOFTMAN ENTERPRIZES -- Dec. 30, 1985
INTRODUCTION:
The software contained in this distribution is copyright (C) by
George Hageman 1985 and is released into the public
domain with the following restrictions:
(1) This software is intended for non-commertial usage.
(2) I am held save from damages resulting from
its use, and
(3) The following concepts and legal jargon are agreed to
by the user of this software.
User-supported software concept:
IF you find use for this software
ANDIF it saves you some development time
THEN send me $10.00
ANDTHENHYP you will feel good!
This source code is provided on an "as is" basis without warranty
of any kind, expressed or implied, including but not limited to
the implied warranties of merchantability and fitness for a
particular purpose. The entire risk as to quality and
performance of this software is with you. Should the software
prove defective, you assume the entire cost of all necessary
repair, servicing, or correction. In no event will the author be
liable to you for any damages, including any lost profits, lost
savings, or other incidental or consequential damages arising out
of the use of inability to use this software. In short my
friends, I have done a reasonable amount of work in debugging
this software and I think it is pretty good but, as you know,
there is always some chance that a bug is still lurking around.
If you should happen to be lucky enough to find one, please let
me know so I can make an attempt to fix it.
The following is a short description of how to use the
inference engine and rule-compiler contained in this software
release. The source and object files for the rule compiler and
the inference engine are contained in the rcomp.lbr and infer.lbr
respectively. There are common files contained in each library.
These common files are header files which are used to define
common terms between the different sources. The most important
header file is the file named "expert.h" which not only contains
common definitions used between the rule compiler and the
inference engine, but has a short description of their usage as
well. This inference engine, and its associated rule compiler,
represents a significant time investment for me, so if you
believe in the shareware concept please remember my address.
George W. Hageman
P.O. Box 11234
Boulder, Colorado 80301
George W. Hageman --1--
INFERENCE -- SOFTMAN ENTERPRIZES -- Dec. 30, 1985
This software compiles using the Microsoft C Compiler Rev
3.0 using the make function which comes with the Microsoft Macro
Assembler Rev. 4.0. I have nothing but good things to say about
these two products and suggest that you consider their purchase
if you are into serious software development for the PC. This
software also compiles and runs under UNIX system V. Use the
UNIXSV flag in the makefile or use a -DUNIXSV when you compile
it.
George W. Hageman --2--
INFERENCE -- SOFTMAN ENTERPRIZES -- Dec. 30, 1985
INFERENCE ENGINES:
An inference engine is merely a program which attempts to
prove consequents given a certain set of antecedents and a set of
rules which define the TRUTH or FALSEness of each consequent in
terms of the antecedents. The consequents, antecedents and
rules for this inference engine are contained in a text file
which is compiled by the rule-compiler into a form the inference
engine can understand. Often these two functions are contained
in the same executeable, but I have decided to split them up to
make the inference engine as small as possible.
Rules are collections of ANTECEDENTS and CONSEQUENTS formed
into TRUTH statements. Each rule is an attempt state that "If
all of the antecedents for this particular RULE are TRUE, then
all of the consequents connected to this rule are TRUE. If one
or more of the antecedents for a RULE are FALSE, then it is
assumed that this rule cannot prove the TRUTH of the consequents,
but this does not necessarily prove the consequents FALSE since
some other rule may prove them TRUE." Rules must have at least
one ANTECEDENT and at least one CONSEQUENT to be considered
valid.
Each ANTECEDENT and CONSEQUENT is a simple statement
consisting of a leading KEYWORD, and a FOLLOWING STRING.
KEYWORDS tell the inference engine what the FOLLOWING STRING will
mean or what is to be done with it. The FOLLOWING STRINGs may be
either in upper or lower case and are either statements such as
"THE ANIMAL IS A BAT", or, a pathname to an executeable which
will be loaded and executed depending on what is defined by the
KEYWORD. Strings, except for the number of leading blanks, can be
considered equal only if they are identical. The reason for this
rule will become apparent later. An example of a pathname
FOLLOWING STRING is "/b1/hageman/expert/storm/gt_3200 data.fil".
Note that the strings denoting pathnames should be exactly as
they would be if the pathname were to be given at a terminal,
also, you may include parameters with any pathname. These
parameters are no different than the parameters that you would
use if you were initiating the executeable from the terminal
rather than via the inference engine. Under MS_DOS these path
names can either be upper or lower case, and for the UNIX
operating system, they must correspond to the exact path name.
George W. Hageman --3--
INFERENCE -- SOFTMAN ENTERPRIZES -- Dec. 30, 1985
QUICK AND DIRTY:
Impatient? Well here are some quick ways to get started
with the inference engine, leave all that reading till later!
ONE:
Use your text editor (WS in the Non-document mode only
Please) to create a quick rule file, or use the animals example
contained in this release. Skip to the next page if you want to
find out what the KEYWORDS are and how to use them.
TWO:
Compile the rules with the rule-compiler by typing..
rulecomp inputfile outputfile
where the inputfile is the filename of the file containing
your rules, and the outputfile is the file inwhich you want the
compiled rules to be written to. Caution, the rule compiler does
not check for the equivalence of the inputfile and outputfile
filenames, if they are identical you will probably have to type
in your rules again.
THREE:
Run the inference engine by typing ..
inference outputfile
answer the questions and go back to step ONE if you found an
error with your rules or you want to expand them.
George W. Hageman --4--
INFERENCE -- SOFTMAN ENTERPRIZES -- Dec. 30, 1985
KEYWORDS:
The following are the KEYWORDS which the rule compiler can
recognize, and a short description of what each means and how
each would be used. Note that the members of each group have
identical meaning and can therefore be substituted for each other
without effecting the sense of the rule. Latter examples will
attempt to demonstrate this fact.
IF, AND, ANDIF:
These KEYWORDS define the FOLLOWING STRING as an ANTECEDENT,
and the TRUTH sense of the string is TRUE if the string is
TRUE. These KEYWORDS can be used interchangeable without
effecting the sense of the rule being expressed.
Example:
IF the animal is a mammal
ANDIF the animal has hooves
AND the animal has horns
This is equivalent to:
AND the animal is a mammal
IF the animal has hooves
ANDIF the animal has horns
Note that since the antecedent part of a rule is essentially
a large AND statement, the order in which the individual
statements are arranged is a matter of esthetics only.
However, it may be more readable to the human, if a certain
order is maintained.
IFNOT, ANDNOT
These KEYWORDS are essentially identical to the above
KEYWORDS except that the sense of the statement is reversed.
That is to say that if the following string is TRUE then the
truth value of the statement is FALSE.
Example:
IFNOT the animal is a mammal
ANDNOT the animal has smooth skin
ANDNOT the animal breaths air
THEN animal is a fish
George W. Hageman --5--
INFERENCE -- SOFTMAN ENTERPRIZES -- Dec. 30, 1985
IFRUN, ANDRUN, ANDIFRUN
These KEYWORDS tell the inference engine that the FOLLOWING
STRING is to be used as a pathname to an executeable. This
executeable is to be loaded and run and the resultant TRUTH
value returned when the routine exits is the TRUTH value of
the ANTECEDENT statement. Like the AND, IF, ANDIF KEYWORDS
above, each of these may be substituted for any of the
others without effecting the sense of the rule statement.
Note that the full path name of the executeable is not
needed if the executeable file resides in the working
directory from which the inference engine was initiated.
Example:
IFRUN /b1/hageman/expert/gt3000
ANDRUN /b1/hageman/expert/sedir direction.dat
ANDIFRUN falling barompress
THEN sorry about the picnic
IFNOTRUN, ANDNOTRUN
These are used as the KEYWORDS above are used -- to initiate
the execution of an ANTECEDENT executeable file, except that
the truth value of the result is reversed as with the IFNOT,
ANDNOT and the ANDIFNOT KEYWORDS.
Example:
IFNOTRUN gt3000
ANDNOTRUN sedir direction.dat
ANDNOTRUN falling barompress
THEN how about a picnic?
THEN, ANDTHEN, THENHYP, ANDTHENHYP
These KEYWORDS tell the inference engine that the FOLLOWING
STRING is a CONSEQUENT. If all of the immediately
proceeding ANTECEDENTS have a truth value of TRUE, then the
inference engine INFERS that the CONSEQUENT is TRUE. The
THEN KEYWORDS ending in "HYP" tell the inference engine that
the FOLLOWING STRING is an ending CONCLUSION and no further
processing or inferencing is required. The routine will
exit when one of the THENHYP or ANDTHENHYP CONSEQUENTS are
proven TRUE. Therefore, one should use the "HYP"
CONSEQUENT KEYWORDS with care.
Examples:
IF you have an aunt
ANDIF your aunt has a child
THEN you have a cousin
IF you have a cousin
THENHYP you have at least two relatives
George W. Hageman --6--
INFERENCE -- SOFTMAN ENTERPRIZES -- Dec. 30, 1985
THENRUN, ANDTHENRUN, THENRUNHYP, ANDTHENRUNHYP
These are similar to the THEN, ANDTHEN etc. KEYWORDS except
they perform the loading and execution of the FOLLOWING
STRING path name if they are proven TRUE. The value
returned by the executeable file loaded becomes the value
remembered for the CONSEQUENT. The truth value for a
CONSEQUENT proceeded with the KEYWORDS of THEN or ANDTHEN is
only remembered if it is proven TRUE. However, with the RUN
type of CONSEQUENT since it is initiated only when found to
be proven, the predicate value it returns is remembered even
if it is FALSE. This prevents the rerunning of CONSEQUENT
routines.
In this manner one can use rules to determine weather or not
a particular routine should be executed, then use the truth
value returned by the routine upon its exit in other rule
statements. An obvious use for such a function would be in
the field of diagnostics. Through a set of rules it could
be determined that a particular diagnostic should be run,
once the diagnostic has been run, further rules could use
the fact of whether the diagnostic test passed (TRUE) or
failed (FALSE) to make decisions about the further isolation
of the hardware failure.
Example:
!
IFNOTRUN isdev1
IFNOTRUN isdev2
IFNOTRUN isdev3
THENHYP there are no devices to run diagnostics on
!
! see note below for the following rule
!
IF isdev1
ANDIFRUN dev1diag
THENHYP device one is faulty
!
IFRUN isdev2
ANDIFRUN dev2diag
THENHYP device two is faulty
!
IFRUN isdev3
ANDIFRUN dev3diag
THENHYP device three is faulty
!
IFNOTRUN dev1diag
IFNOTRUN dev2diag
IFNOTRUN dev3diag
IFRUN isdev1
ANDRUN isdev2
THENRUN diag12
!
!
George W. Hageman --7--
INFERENCE -- SOFTMAN ENTERPRIZES -- Dec. 30, 1985
!
IFRUN diag12
THENHYP device two is suspect remove and re-run test
!
IFNOTRUN diag12
THENHYP device one is suspect, remove and re-run test
!
Note:
You have probably noticed that the FOLLOWING STRINGS
associated with the RUN KEYWORDS and the IF, AND etc.
KEYWORDS are interchangeable. This is due to fact that the
TRUTH of a string is kept as a pointer into the string
buffer, and therefore have no information concerning their
nature and only have meaning when used in conjunction with a
KEYWORD. If you are sure that the string "isdev1" will have
its truth determined earlier by running the routine
"isdev1", Then you may use it as a regular string in later
rules, however, if its truth has not been determined then
the inference engine will ask you for the truth of the
statement "isdev1" rather than running the routine. To be
sure use the "RUN" form for the strings which relate to
executeables, they will only be run once as it is, so you
don't really have to keep them straight.
Notice also that if the first rule is not proved by the
fact that isdev1 turns up being TRUE and therefore the
antecedent statement is FALSE due to the reverse sense of
the IFNOTRUN KEYWORD, then the others will not be run until
they are encountered in other rules containing them. So be
safe and use the RUN forms of the KEYWORDS if you intend the
execution of an object.
George W. Hageman --8--
INFERENCE -- SOFTMAN ENTERPRIZES -- Dec. 30, 1985
USAGE:
Ok, now that we know what all the key words are, how does
one go about using an inference engine, and more specifically how
does one use this inference engine and what for?
People usually use inference engines as part of what are
known as expert systems. Expert systems are a study associated
with a branch of software engineering known as Artificial
Intelligence (AI). (I am probably going to get some heat from
that statement). Expert systems are supposed to mimic the way
in which human experts deal with a particular physical or mental
problem. A clear example is an expert system which could
isolate a fault within a complex computer system as well as or
almost as well as its human counterpart. It is apparent that
the computer expert system would lack much of the tactile
resources the human expert would have, but the computer expert
could still be of great value when coupled with a novice computer
user. In this way the computer expert would rely on the human
to perform actions and observations the computer expert is
incapable of doing. The computer expert and the novice then
could form a team which might perform as well as the human expert
alone and at a probably much lower per/hour labor rate.
Unfortunately, in order to develop an expert system, one
must either be an expert in the area one wants to develop an
expert system for or have a ready access to one. Assuming that
you are or have found one, the following is a description of how
one would use the inference engine and the rule compiler to
produce an expert system. Fortunately one of the sticker tasks
of developing the inference engine has been done, and all you
have to do is develop the rule base, compile it with the rule
compiler and use the resultant compiled rule-base file as a
parameter when you initiate the inference engine. In reality
this is a much tougher job than developing the inference engine.
Expert systems generally consist of three parts, a
KNOWLEDGE BASE, HUMAN INTERFACE, and an INFERENCE ENGINE. The
following is a short description of each:
THE RULE or KNOWLEDGE BASE:
The rules consisting of ANTECEDENTS and CONSEQUENTS are
known as the "KNOWLEDGE BASE" of the expert system. An
additional part of the KNOWLEDGE BASE consists of the executeable
files and their shared data files. The way the "knowledge
engineer" puts these rules together determines how good and/or
effective the resultant expert system becomes. The KNOWLEDGE
BASE is the smarts of the expert system, and the basic data on
which the inference engine is to operate upon.
George W. Hageman --9--
INFERENCE -- SOFTMAN ENTERPRIZES -- Dec. 30, 1985
THE HUMAN INTERFACE:
The expert system needs a way to ask the human user about
the TRUTH or FALSENESS of the antecedents contained in the rule
base. This is contained as a part of the inference engine
associated with this release. These routines will ask the user
whether or not FOLLOWING STRINGS are TRUE or FALSE. Additional
human interfaces may be contained in the executeable files.
THE INFERENCE ENGINE:
The inference engine released with this software is known as
a backwards chaining inference engine. It works by identifying
consequents and attempting to find rules to prove that each
consequent is TRUE. Once a consequent is proved TRUE, it is
remembered as being TRUE. Each antecedent which is determined
either TRUE or FALSE is remembered so that the user does not have
to be asked more than once to verify a particular statement.
Remember that if a consequent is not proved TRUE, then it does
not necessarily mean that it is FALSE. For more information
consult the "inference.str" file which is a preliminary pseudo
code description of the inference engine. It is not correct
because I have not gone back and up dated it from the
implementation effort (Tom De Marco please forgive me) but, it is
close enough to provide a basis for understanding the code. I
suggest looking at the code to understand how this inference
engine works. I have also left in all of the debug statements
which I found helpful so by modifying the makefile to include the
DEBUG FLAGS, you can observe the inference engine working.
This inference engine attempts to prove all of the
consequents from the top of the rule base through to the bottom
in a linear way if possible. If however, an antecedent is really
a consequent of a rule, the inference engine will attempt to
prove that consequent even if it occurs later in the rule base.
In this sense, the inference engine will exhibit some forward
chaining characteristics.
There are several good books on the development of expert
systems, inference engines and the like. I have included a
bibliography which contain the books I consulted to build this
one.
George W. Hageman --10--
INFERENCE -- SOFTMAN ENTERPRIZES -- Dec. 30, 1985
BUILDING EXPERT SYSTEMS:
The builders of expert systems are sometimes known as
"knowledge engineers". As the name implies, they deal with the
manipulation and representation of knowledge leading to the
development of the Knowledge base the inference engine operates
upon. In order to develop the knowledge base the knowledge
engineer needs either to be an expert in the area for which the
expert system is to be developed or, have ready access to a human
expert in the field.
The inference engine in this distribution accepts knowledge
in many ways. The first of which are the rules as discussed
above which are relatively simple logical or predicate statements
about the TRUTH of well defined consequents. The other is the
somewhat complex knowledge representation as contained in the
executeable files which may be initiated by the inference engine.
In fact, the inference engine and the rule_compiler each can be
one of these executeable files so you can have recursive expert
systems if you have a mind to! You can even use another
executeable to produce a text file of rules, which then can be
operated on by the rule-compiler and then fed to another
inference engine producing self-modifying or learning expert
system. So even though the inference engine is only 12K and the
rule compiler 10K these are sufficient enough to produce rather
powerful expert systems.
To develop the knowledge base the knowledge engineer first
must under stand the limitations which are acceptable to the
expert system user. For example, if the user of an animal
identification expert system is not concerned with whether the
expert can differentiate between a snake and a lizard or is
not interested in reptiles at all, then the expert system can be
simplified by leaving out this knowledge. Once the boundaries
of an expert system are well known, the expert system designer
can concentrate on how to define the particulars. This software
release contains two examples of simple expert systems. The
first is the more or less classical animal identification expert,
and the second is a weather predictor expert which demonstrates
the usage of the IFRUN, ANDTHENRUN, etc. KEYWORDS.
George W. Hageman --11--
INFERENCE -- SOFTMAN ENTERPRIZES -- Dec. 30, 1985
ANIMALS:
This is a simple expert which can differentiate between only
certain types of animals -- Mammals and Birds. And among these
two groups it can only tell you that the animal you are thinking
about is either a Giraffe, Zebra, Cheeta, Tiger, Penguin,
albatross, Duck, and so on. The example has been limited to
these few identifications in order to greatly simplify the
development effort and to help demonstrate the strategy of
developing the rules associated with this simple expert system.
The strategy associated with the development of a consistent
set of rules which will identify a particular animal given
certain physical characteristics to work with is DIVIDE AND
CONQUER. The idea being to use rules which build a decision
tree where each branch of the tree is formed by a rule which can
decide which direction to go at that junction. Since we are
obviously dealing with birds and mammals then we can build our
root branch or the grossest division as a rule which can
differentiate between birds and mammals. Like:
!
IF animal gives milk
ANDIF animal has hair
THEN animal is mammal
!
IFNOT animal is mammal
THEN animal is bird
!
.
.
Notice that if the animal is not a mammal we automatically
assume that it is a bird since this is the domain of our expert
system -- it does not consider any other type of animal as a
possibility. If we were to include perhaps reptiles then the
following might be used instead:
!
IF animal gives milk
ANDIF animal has hair
THEN animal is mammal
!
IFNOT animal is mammal
AND animal has feathers
AND animal lays eggs
THEN animal is bird
!
IFNOT animal is mammal
IFNOT animal is bird
THEN animal is reptile
!
George W. Hageman --12--
INFERENCE -- SOFTMAN ENTERPRIZES -- Dec. 30, 1985
Again the last category is the default and needs no further
definitions because it is within the limitations of the expert
system.
Further refinement of the decision tree associated with the
animals expert should build on the knowledge gained by earlier
branching. So one should use the knowledge that the animal has
been identified as a bird to further define the animal. An
example of the further definition of the type of mammal follows:
!
IF animal is mammal
ANDIF animal eats meat
ANDIF animal eats little vegetation
THEN animal is carnivore
!
IFNOT animal is carnivore
ANDNOT animal eats little vegetation
THEN animal is vegetarian
!
Finer and finer branching is achieved by this divide and
conquer strategy until the leaves of the tree are reached, These
leaves are the actual hypothesis which end the search for a
particular animal.
.
.
!
IF animal is cat
AND animal has tan color
AND animal has stripes
THENHYP animal is tiger
!
IF animal is cat
AND animal has tan color
AND animal has spots
THENHYP animal is cheeta
!
.
.
Notice that "animal is cat" should be a THEN Consequent
somewhere or else the inference engine will simply ask you if the
"animal is cat" statement is TRUE or not -- which may not be
construed as a particularly intelligent thing for an expert
system to do. The intelligence represented by the expert system
is directly related to the intelligence you give it. However, it
is possible to get very confused when there are a large number of
rules for a particular expert system and mistakes in logic or the
development of circular logic occurs. The first will cause
incorrect conclusions to be drawn and the second will cause the
inference engine to crash. Circular logic causes the inference
engine to run out of stack space.
George W. Hageman --13--
INFERENCE -- SOFTMAN ENTERPRIZES -- Dec. 30, 1985
A circular argument is an argument which cannot be resolved
because its proof relies on another rule which in turn relies on
proving the first statement before it can be proved such as in:
!
IF the second one is true
THEN the first one is true
!
IF the first one is true
THEN the second one is true
!
Or to expand the concept:
!
IF the third one is true
THEN the first one is true
!
IF the first one is true
THEN the second one is true
!
IF the second one is true
THEN the third on is true
!
Usually, when the inference engine tells you that "Stack
overflow" has occurred -- this will be the problem.
Look at the animal file contained in this release, see how
the rules are built and as an exercise add another animal to be
differentiated like a platypus, and later add a whole class of
animals such as domestic farm animals, or even a division such as
reptiles or insects.
You will soon notice that your knowledge base will increase
very quickly with each set of animals you want your expert to
differentiate. With this growth of the knowledge base come real
difficulty in keeping the rules correct and non-circular. A
strategy for limiting the complexity for these rules is to use
the IFRUN or THENRUN capability of this inference engine to fire-
up a whole new inference engine which is an expert in one of the
major branches of animals. In this manner one only has to make
the major decisions associated with a class of animals and then
run the expert system which knows how to handle the specific
class of animals.
George W. Hageman --14--
INFERENCE -- SOFTMAN ENTERPRIZES -- Dec. 30, 1985
For example:
!
IF animal has feathers
AND animal lays eggs
THEN animal is bird
THENRUNHYP inference.exe birds.cmp
!
IFNOT animal is bird
AND animal has hair
AND animal gives milk
THEN animal is mammal
THENRUNHYP inference.exe mammals.cmp
!
The files "birds.cmp" and "mammals.cmp" are the resultant
compiled files from the text knowledge bases "birds" and
"mammals" which the knowledge engineer would need to produce.
But, as stated above, these files would represent expert systems
knowing only the limited area of birds or mammals and therefore
can be greatly simplified. NOTE: inference.exe returns a TRUE
value if it has proved anything while it ran, and FALSE if it
could not prove anything. With an IBM AT with 512 KBYTES of
memory I was able to load four copies of an inference engine
simultaneously. A good way to see how many your system can deal
with at the same time compile the following test:
!
IFRUN INFERENCE.EXE TEST.CMP
THENHYP I am done
!
If this file is named TEST, then compile it using the following:
rulecomp test test.cmp
Then, run the inference engine with the test.cmp file as follows:
inference test.cmp
Notice that when any routine cannot be run for some reason
or another, an attempt is made to tell you what went wrong -- out
of memory, can't find it, or some other reason, and the routine
will be assumed to have returned normally with a TRUE predicate
value. This is done so that the inference engine won't simply
die at some mysterious point. The "I infer that : I am done" at
the top was the last inference engine which could be loaded which
could run but could not spawn a new process, the next one down is
the last one which could spawn one, and any others below this
line plus this one will tell you the number of levels of the
inference engine you can run on your system.
George W. Hageman --15--
INFERENCE -- SOFTMAN ENTERPRIZES -- Dec. 30, 1985
THE WEATHER EXPERT:
The other expert system knowledge base included with this
release is a weather predicting expert. This expert system
demonstrates the use of executeable files to expand the
abilities of the inference engine to deal with other forms of
knowledge. Look a the source files for the weather expert,
notice how each member of this set of routines uses a common file
for the transfer of needed data. The need of a file for this
transfer of data is done because it was the only standard form of
data transmission which was not machine dependent according to
MS-DOS and UNIX operating systems. Specific methods for dealing
with this problem can be found for your machine which can greatly
speed up this cumbersome data transfer method -- but it works.
UNIX and the Microsoft C compiler allows a routine to exit
with a value which will be returned to the parent process. This
method is used to allow each executeable to return its TRUTH-
VALUE or PREDICATE-VALUE back to the inference engine. The
routine runRoutine(consequent) performs this task. If you look
at the file runrouti.c you can see that this is done with the
"exit(value) ;" statement. The values used to indicate the TRUTH
and FALSEness of the routine are "RETURN_ROUTINE_TRUE" and
"RETURN_ROUTINE_FALSE" as contained in the header file
"routine.h". This header file should be included in any routine
which returns a TRUE/FALSE value to the inference engine.
The strategy for using this method of expanding the
knowledge base is essentially the same as that for the animal
type expert system, except that it is noticed that the simple
form of the knowledge base does not have the capability to
perform some of the functions needed. Cases where complex
questions or the manipulation of data are necessary must resort
to the use of executeable files which can deal with them. Such
is the case for the weather predicting expert system.
The weather expert must deal with such data as barometric
pressure, wind direction, and the current rate of change of the
barometric pressure. Additional data such as cloud conditions
can be handled by the predicate functions of the inference
engine. Again the strategy is to divide and conquer by
determining which information needs to be gathered by the
executeable portion of the expert system, what routines must be
used to convert this data into a form which is usable by the
inference engine i.e. TRUE or FALSE, and, what information can
be gathered directly by the inference engine. Once these
decisions are made then a decision tree can be built in a similar
manner to the one built for the animal expert but also
incorporating the executeable files where appropriate. Look at
the file "weather" and at each of the source files for the
executeable portion of the weather expert.
George W. Hageman --16--
INFERENCE -- SOFTMAN ENTERPRIZES -- Dec. 30, 1985
Notice that there is a "main" routine (even though all of
the programs are stand-a-lone programs and are have the name
"main"). This routine is in the file "MESSAGE1.C", and provides
the data entry for all of the data needed by the expert system.
The routine explains to the user what is needed, checks for
reasonable responses, and writes the data to a disk file for
later use by the other routines associated with this system.
These other routines, when initiated, have the task of reading
the disk file produced by the "MESSAGE1.EXE" executeable, check
for some conditions, and return "ROUTINE_RETURN_TRUE", if the
conditions are met and "ROUTINE_RETURN_FALSE" if they are not.
In this manner the knowledge engineer can make expert
systems of a higher complexity and usefulness than would
otherwise be possible.
CONCLUSION:
I hope that this short definition of the inference engine is
enough to get you started into the fascinating field of AI.
There are some useful additions the enthusiastic programmer could
make to the inference engine to both enhance its usefulness and
its ability to assist in the debugging of knowledge basses. A
"Why" function which shows the complete logical path which lead
to the question being asked, showing each statement as being
known or unknown and if known what its predicate value is, would
be very helpful. Further, the addition of different KEYWORDS
such as an OR function, might expand the usefulness of the
inference engine. I may include these in my next release of this
software but If you have made such an addition -- I will include
them in the next release and refund your $10.00 if you have been
so good as to send it to me.
Good luck and if you have any questions or would like to
discuss this concept please drop me a line.
Thanks,
George W. Hageman
George W. Hageman --17--
INFERENCE -- SOFTMAN ENTERPRIZES -- Dec. 30, 1985
BIBLIOGRAPHY:
The following books and articles were helpful in the
development of this inference engine.
MVP-FORTH EXPERT SYSTEM TOOLKIT, Jack Park, Mountain View
Press, Inc. P.O. Box 4656 Mountain View, CA 94040 Phone: (415)-
961-4130.
MVP-FORTH EXPERT-2 TUTORIAL, Mitch Derick and Linda Derick,
Mountain View Press.
INSIDE F83, C. H. Ting, OFFETE ENTERPRISES, INC. Available
from Moutain View Press.
Expert Systems and the Weather, Jack Park, Dr. Dobb's
Journal, April 1984, pp. 24-28.
Programming in Prolog, William F. Clocksin and Christopher
S. Mellish, Springer-Verlag
LISP, Patrick H. Winston and Berthold Klaus and Paul Horn,
Addison Weseley.
A special thankyou to Jack Park and the MVP-FORTH EXPERT
SYSTEM TOOLKIT. Many of the ideas in this document and the
development environment afforded by FORTH were the starting point
for many of the ideas developed in this inference engine. If you
are into FORTH this is an excellent source of information on the
subject.
George W. Hageman --18--
---------------------- Cut Here --------------------------------
George Hageman ( ...bmcg!asgb!benish!hageman )
Happy New Year!greg@unlv.UUCP (Greg Wohletz) (01/04/86)
Followup-To: In article <831@asgb.UUCP> hageman@asgb.UUCP (George W. Hageman) writes: >The following is the documentation file for an inference engine >written in C. There will be three other submittals to net.souces >consisting of the source for a rule compiler, inference engine, and, >a weather prediction expert rule base including an animals expert. > >Have fun.... > >----------------------- Cut Here ----------------------------- > > INFERENCE -- SOFTMAN ENTERPRIZES -- Dec. 30, 1985 > > > INTRODUCTION: > > The software contained in this distribution is copyright (C) by > George Hageman 1985 and is released into the public > domain with the following restrictions: > > (1) This software is intended for non-commertial usage. > (2) I am held save from damages resulting from > its use, and > (3) The following concepts and legal jargon are agreed to > by the user of this software. > > User-supported software concept: > > IF you find use for this software > ANDIF it saves you some development time > THEN send me $10.00 Of course you plan on sending that money to the backbone sites to cover the cost of transmitting this stuff, don't you? > ANDTHENHYP you will feel good! > > This source code is provided on an "as is" basis without warranty . . legal mumbo jumbo . . > believe in the shareware concept please remember my address. I do, but what I don't agree with is the concept of having others pay to distribute your software when you have no intention of (even if there was a way to) reimbursing them. > > George W. Hageman > P.O. Box 11234 > Boulder, Colorado 80301 --Greg most nets: greg%unlv@CSNet-Relay or for domainites: greg@unlv.csnet usenet: seismo!unr70!unrvax!unlv!greg