Chris, (01)
JFS>> ...The old KIF 3.0 had a backquote, which I used to
>> support contexts in conceptual graphs (which were influenced
>> by Peirce's contexts, which have similar expressive power
>> to McCarthy's contexts). I was very happy to get the 'that'
>> operator in IKL, which can be used in the same way as backquote. (02)
CM> It is semantically superior to backquote, however, especially
> for representing intensional contexts. Intuitively, what we
> believe, fear, desire, etc are propositions (or states of affairs,
> etc -- whatever structured entity you take that-clauses to denote),
> not sentences. (03)
I agree that the 'that' operator is more appropriate for propositions
than the KIF backquote. Since the concepts in conceptual graphs
have a type label, I introduced a kind of "type coercion" in my
original 1984 book. (04)
For example, consider the conceptual graph for the sentence
"The cat Yojo is on a mat." In CGIF, it would be represented, (05)
[Cat: Yojo] [Mat *x] (On Yojo ?x) (06)
Or in the older linear notation, which is slightly more readable, (07)
[Cat: Yojo]->(On)->[Mat] (08)
If I want to refer to that graph as a graph, I can write (09)
[Graph: [Cat: Yojo]->(On)->[Mat]] (010)
But I might want to refer to the proposition whose statement (Stmt)
is that graph: (011)
[Proposition]->(Stmt)->[Graph: [Cat: Yojo]->(On)->[Mat]] (012)
By the convention of type coercion, a graph nested inside a concept
of type Proposition is used to state the proposition. Therefore,
the above graph can be abbreviated as (013)
[Proposition: [Cat: Yojo]->(On)->[Mat]] (014)
The following graph represents a situation described (Dscr)
by a proposition stated by the nested graph: (015)
[Situation]->(Dscr)->[Proposition: [Cat: Yojo]->(On)->[Mat]] (016)
And by a second application of type coercion, this graph could
be abbreviated as (017)
[Situation: Yojo]->(On)->[Mat]] (018)
In translating CGs to KIF 3.0, I mapped the concepts of type Graph
to a KIF expression that used backquote. The concepts of type
Proposition and Situation used type coercion. (019)
John (020)
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