Lynda,
There have been many different incompatible implementations of
conceptual graphs. But today there is only one official standard:
Annex B of the ISO/IEC standard 24707 for Common Logic.
> I have found different definitions for a conceptual graph. There
> are articles which define it as being a connected graph and of the
> other one define it as being a not necessarily connected graph.
On page 73 of my 1984 book, _Conceptual Structures_, I stated:
"A conceptual graph is a finite, connected, bipartite graph."
For most practical purposes, the restriction to connected graphs
merely made a difference in how you counted them. But it was
inconvenient for the theory, because it created unnecessary
special cases. Therefore, I and most other people dropped it
in later publications. The ISO standard does not make any
such restriction.
For a brief summary of the ISO standard CGs, see the article
in the Handbook of Knowledge Representation:
http://www.jfsowa.com/cg/cg_hbook.pdfFor the official definition, please download the ISO standard:
http://standards.iso.org/ittf/PubliclyAvailableStandards/c039175_ISO_IEC_24707_2007(E).zipFor the CGIF grammar rules in a much smaller file, see
http://www.jfsowa.com/cg/cgif.htmI strongly urge everyone to adopt the ISO standard. That is
the only reliable basis for compatibility among all CG tools.
But as I say in the paper cg_hbook.pdf, there are good reasons
for research that explores future extensions. However, those
extensions should build on the standard.
John Sowa
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