From: Richard Fikes ([email protected])
Date: 06/25/02
Here are a couple of query examples for today's discussion. These
examples are intended to be illustrative of aspects of the current
design of DQL rather than being illustrative of typical query-answering
cases.
The first example illustrates answers that contain bindings for only
some of the "may bind" variables in cases where an answer is inferable
(from a min-cardinalityQ restriction in the example) and where an answer
is an anonymous node.
KB0:
* Class "Red-Car".
* Class "Red-Car-Owner" with a min-cardinalityQ restriction of 1 and
hasClassQ "Red-Car" on property "has-car" (i.e., every Red-Car-Owner has
at least one car that is a Red-Car).
* (type RC1 Red-Car)
* (has-car Bill RC1)
* (type Joe Red-Car-Owner)
* (has-car Fred _:r)
* (type _:r Red-Car)
QUERY-01:
query pattern: (has-car ?p ?c) (type ?c Red-Car)
must bind: ?p ?c
answer KB: KB0
One answer: {[?p/Bill], [?c/RC1]}
QUERY-02:
query pattern: (has-car ?p ?c) (type ?c Red-Car)
may bind: ?p ?c
answer KB: KB0
Three answers: {[?p/Bill], [?c/RC1]}, {[?p/Joe]}, and {[?p/Fred]}
QUERY-03:
query pattern: (has-car ?p ?c) (type ?c Red-Car)
may bind: ?p
don't bind: ?c
answer KB: KB0
Three answers: {[?p/Bill]}, {[?p/Joe]}, and {[?p/Fred]}
------------------------------------
This is an example of an answer being inferable from the existence of an
instance of a class and a cardinality restriction.
KB1:
* Class "Country".
* Class "Person" with a cardinality restriction of 1 and a valueType
restriction of "Country" on property "country-of-birth" (i.e., every
person has exactly one country-of-birth and a person's country-of-birth
is a Country).
* (type Bill Person)
QUERY-11:
query pattern: (type ?x Country)
must bind: ?x
answer KB: KB1
No answers.
QUERY-12:
query pattern: (type ?x Country)
may bind: ?x
answer KB: KB1
Query has one answer. The answer has an empty set of bindings. The
answer corresponds to a proof that since there is a person and that
person has a "country-of-birth" that is a Country, then there exists a
Country (i.e., an ?x such that ?x is type Country).
QUERY-13:
query pattern: (type ?x Country)
don't bind: ?x
answer KB: KB1
Query has one answer. The answer has an empty set of bindings. As with
QUERY-2, the answer corresponds to a proof that since there is a person
and that person has a "country-of-birth" that is a Country, then there
exists a Country (i.e., an ?x such that ?x is type Country).
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