Our mereological ontology is simply an Ontolingua implementation of the
Classical Extensional Mereology as described in [Simons, 1987]. We
therefore only give a brief explanation of this ontology and refer to
[Simons, 1987] for the details and more philosophical aspects. Two
relations define part-of decompositions. The relation `equal(x,y)`
defines which individuals are to be considered mereologically
equal. In the usual case, it only holds for `equal(x,x)` but in
some situations it is convenient to say that two individuals are equal
when they have the same parts. An individual `x` is a mereological
individual when `equal(x,x)` holds. When a mereological individual
`x` is a part of a mereological individual `y`, the relation
`proper-part-of(x,y)` holds. With these relations it is
possible to write down a variety of axioms specifying desirable
properties any system decomposition should have. Examples are the
asymmetry and transitivity of the `proper-part-of` relation.

**Figure 3:**
Excerpt from the mereological ontology. This ontology defines the
means to specify decomposition information and the properties any
decomposition should have.

Figure 3 shows an excerpt from the mereological
ontology. Definition 2 defines the class of mereological individuals
that was sketched above. The definition of the `proper-part-of`
relation clearly shows the asymmetry (3a) and transitivity (3b) axioms.
Note that these definitions only serve as an illustration and are not
meant to be complete. The ontology furthermore defines the relation
`disjoint(x,y)` which holds for individuals that do not share a
part and `simple-m-individual`, the class of individuals that have
no decomposition.

Fri Sep 27 13:28:43 MET DST 1996