A Taxonomy of Symbols

All symbols in the ontology are alphanumeric strings with the addition of only the hyphen character. No accents are permitted on any of the characters. Such enhancements are permitted only in lexicons. As far as ontology development is concerned, all symbols that we encounter can be classified into one of four types:

• concept names: typically English words with at most four words in a name separated by hyphens.
• instance names: following the standard practice in AI, an instance is given a name by appending its concept name with a hyphen followed by an arbitrary (but unique) integer.
• special slot names: is-a, subclasses, definition, instances, instance-of, time-stamp, domain, and range. These are not defined as properties in the ontology.
• literal constants: these are also usually English words, in fact single words most of the time.
• the special symbol *nothing*: used to block inheritance as described below.
• other miscellaneous symbols used in the K system including:
  • TMR symbols
  • lexicon symbols
  • numbers and mathematical symbols
  • other extraneous symbols (which are detected and eliminated using a set of quality control programs)

Brief listings/glossaries of TMR and lexicon symbols are provided in the accompanying report by Mahesh and Wilson (1995). Ideally, numbers are not present either in the lexicon or the ontology (though for current purposes we may have added some to the lexicon). They are recognized as numbers by a morpho-syntactic analyzer (such as the Panglyzer system from the Pangloss (1994) project) and directly incorporated into the TMR. Mathematical symbols such as the multiplication and division operators, * and /, are used in certain slot fillers in the ontology, such as, for example, to represent conversion factors between different measuring units. All other symbols are ``other extraneous symbols'' that should not be present.

• Characteristics of Literal Symbols