Expert Systems Using TMYCIN

Identification of Snakes

The TMYCIN inference engine provides a general framework for defining and utilizing rules for an expert system. This program comes with two sample rule bases, a very simplistic database for identifying rocks and a moderate database for identifying some snakes. A more extensive database also has been developed, using an expanded version of TMYCIN, for advising incoming students which courses they should take first at Grinnell College.

Identification of Rocks

To gain some experience with TMYCIN, run the rocks expert system:

1. Run the acl interpreter.

2. Load the database with the command:

   (load "~walker/261/labs/rocks.lsp")
   

   Note that the database automatically loads the TMYCIN inference engine as well.

3. Start a session with the command:

   (doconsult)
   

4. Answer the questions asked. For the first case, you might specify that the color is black, the rock is not pretty, and its hardness is 4.

   Note that the expert system will prompt you for the conclusion, if the data do not fit the rules known.

5. After the expert system identifies a rock, issue the commands

   (why)
   (whynot obsidian)
   

   Describe what happens.

6. After reading Section 2.1 of the documentation, look at the data file ~walker/261/labs/rocks.lsp to identify the context name, the parameters, the initial data, and the goals for this file.

7. From the data file, write in English the content of the three rules.

8. From the dialog, explain why each question was asked. Looking at various runs of the program, does it seem that the program asks the same sequence of questions in each case? Why or why not?

Identification of Snakes

For a more interesting session, we consider the snakes database, found in file ~walker/261/labs/snakes.lsp.

1. After loading this database, run several test sessions. For example, run the following cases:
   • a tiny, tan snake found under leaves
   • a large, yellow snake with blotches, but not a triangular head and no rattles
   • a large, brown snake with diamond pattern, but not a triangular head and no rattles
   • a tiny, solid-red snake with no rattles, but which has bitten someone showing two larger fangs

   In each case, what questions are asked and what conclusions are drawn?

   For each result, note for future reference the identification number (e.g., snake844) given by TMYCIN.

2. After some of these, ask (why) or (whynot ---), following the discussion in Section 7.2 of the documentation.

3. Check some rules in the database with the following commands:

   (showrule 'rule01)
   (englrule 'rule01)
   

4. TMYCIN stores information about each snake as a property list associated with the snake's identification number, and the showprops command retrieves this information by identification. For example,

   (showprops 'snake844)
   

   retieves the property list for the snake with identification snake844.

   Use showprops to examine the property lists for the tests you ran earlier.

5. Examine the rule-base file ~walker/261/labs/snakes.lsp to identify the context, parameters, initial data, and goals.

   Use this information, together with the rules, to explain why the program followed a particular line of questioning for the test cases you ran earlier.

The Department of Mathematics and Computer Science uses an expert system to help advise students about which mathematics and computer science courses they might take first. The program, which expands TMYCIN, was first developed in the Spring, 1993, as a student-faculty project; students Vikram Subramaniam and Ivan Sykes worked with faculty member Henry Walker. The program has been refined and expanded several times over the years to reflect new or revised courses.

Input includes high school transcript information and standardized test scores; the program then suggests a first mathematics course and a first computer science course for a student. The program can be used interactively with the user entering needed data, or the program can process information received electronically from the Registrar. In this latter mode, the program can generate letters for students.

Click here, if you would like instructions to run various forms of this program.

The TMYCIN Program

The code for TMYCIN is found in ~walker/261/labs/tmycin.lsp. Review this LISP code as you have time to identify relevant parts and algorithms of this program.

http://www.math.grin.edu/~walker/courses/162/lab-expert-sys.html