Information Technology Reference
In-Depth Information
7.
george is a father of sue.
(by virtue of sentences 3, 1, and 5)
8.
sue is a parent of jane.
(by virtue of sentences 2 and 4)
9.
george is a grandfather of jane.
(by virtue of sentences 7, 8, and 6)
So in all three cases the query is logically entailed by the KB. Now let us consider
some examples of sentences that are
not
logically entailed:
gina is female.
This sentence may indeed be true. After all, Gina is a name that is commonly
used by females. However, although the constant
gina
appears in the KB, it could
just as well have been
harvey
or
person17d
. No connection to
female
is warranted.
john is younger than sam.
Someone might say, “If everything in the KB is true, then John is a child of Sam,
so he has to be younger than Sam. So the query must be true.” This is not quite
right, but the reason may not be obvious. It cannot be assumed that the symbol
younger
means the same as it does in English. In deciding what is entailed, the
only information that may be used is what actually appears in the KB (see
parent
and
grandfather
). Since the symbol
younger
does not appear in the KB, there is
no information to use. The query could be written as
john is in relation239 to sam
which, of course, need not be true. So the query is not logically entailed.
sue is a mother of john.
This is similar to the previous case. The following two sentences are entailed by
the knowledge base:
sue is female.
sue is a parent of john.
But one cannot conclude that the sentence
sue is a mother of john.
is true. One might want to make a connection between
mother
and the symbols
female
and
parent
, since that is how it works out in English. But nothing in the
KB currently sanctions this. This is quite unlike the
father
case, where sentences
in the KB do connect
father
,
male
, and
parent
.
