A POP-11 library called semnet provides procedures for making inferences from items stored in the POP-11 database. For the procedures to work, the database must contain items in the form of triples, with the middle `relation' item being a single word -- for example,
[[the natural history museum] isa [museum]]
This is exactly the form that we have used for the examples in the previous chapters. The procedures names are the same as the normal database ones, plus an initial `s', and they perform in a similar manner. Certain key words, however, enable the inferences to be made; the ones that we shall be using in the examples are `connects' and `isa'. In this section we shall not make a distinction between isa and ako links, though often it is wise to do so, as properties of sets may not always also be properties of individuals. For example, while we know that there exist animals of both sexes, and that therefore there exist mammals and, after that, dogs of both sexes, we would not consequently want to deduce that Fido too is therefore of both sexes.