YACC Grammar for the linear form of a Conceptual Graph
I have tried to put together, using code I developed for my honours
project, a sample parser for the linear form of a Conceptual Graph.
Hopefully this will give an idea of how such a parser may be constructed
and provide some insight into the issues involved. I have put the code
together rather quickly (cutting, pasting and adding to the original code
I had - especially, I removed a lot of problem specific code that is of
little use to others). So, the code is neither elegant nor efficient
(far from it) but, I hope it is relatively bug free.
The following files are included:
README - this file
README1 - email message sent to Gerard Ellis discussing an appendix
to my thesis (see below).
gram.skel.y - skeleton grammar for linear form.
cog.y - implementation of grammar for linear form.
Note: not all of the grammar from gram.skel.y has
been implemented. Also, the code may make it harder
to read than gram.skel.y
cog.h - include file for sample application.
parse.c - C code for sample application
(lexical analyser, symbol table, etc.).
Makefile - Makefile for sample application
Test - Directory containing very simple
(and very meaningless) tests
Interesting files are test3 and test4 - from Sowa's book.
grammar.app.mm - appendix from my thesis contrasting 3 grammars for
- CoGNO - my honours project
("CoGNO - A Graphical User Interface to Conceptual Graphs", Nov 1990)
Rao, A. S. and Foo, N. Y.,
"CONGRES - Conceptual Graph Reasoning System",
in Proc. 3rd IEEE Conference on AI Applications, Orlando, Florida.
(I actually looked at the code to work out the grammar
- sorry for any errors made.)
"Knowledge Representation Environment for Shared World Knowledge"
Technical Report 88/3, Department of Computer Science, James Cook`
University of North Queensland, Australia, 1988.
tbl grammar.app.mm | eqn | troff -mm | <printer>
Notes on the sample application
- Compile by typing: make
- Run by typing: cogno <files...>
or cogno (expects input from stdin)
- Data structure used: edge list
i.e there is a linked list of nodes. Each node in this list
has a linked list of "edges" which are pointers to nodes
(signifying that there is an edge from the node "towards"
each node on its edge list)
- All commas must be inserted. I have not taken care of the condition
where all commas preceding a period may be omitted.
This could probably be handled by the lexical analyser.
- Remember that every relation must have one (and only one) arc exiting
In some cases it is not possible to immediately determine the orientation
of arcs connecting relations listed after a dash "-" .
I have delayed the choice by pushing relation/concept node pairs
onto a stack - when the end of the graph is reached I resolve
any directions by looking at the node pairs: if the relation
does not have an arc exiting it then I make a connection
from the relation to the concept otherwise I make a connection
from the concept to the relation.
This is ok in most cases but, Sowa mentions that numbering arcs
can also be used to resolve this problem - I have neglected
arc numbers but they should be checked.
One other check that should be performed here is to ensure that
each relation has one arc exiting from it.
This shouldn't be too hard to implement.
At present the graph [A]->(B) will be accepted!
- In the sample application nested subgraphs are treated as separate entities -
I do not make any attempt to associate them to the node in which they are
nested. Also, the memory they use is deallocated after they have been
- The two shift reduce errors produced on running the grammar through yacc
are due to the <sep> rule as a result of the newline character (\n)
being significant - you can probably get rid of them using yacc's %left
but they don't affect the result anyway.
- I don't treat the word PROPOSITION in any special way (I did at one time -
but it's just a concept type label and therefore I don't consider
it to have any special meaning even though in most cases it does).
Any concept label can be used in a concept node with nested
- Not much checking is done - some others that may be performed are commented
into the code. (e.g., in type definitions we should check that
the parameter supplied actually exists in the graph).
- The sample application exits immediately if a syntax error is detected
you may wish to modify this behaviour.
- Unfortunately I have put this together in haste. Therefore I am sorry
for any errors, lack of information and clarity, etc., that exists.
I hope that the grammar may be of use.
Basser Department of Computer Science
Madsen Building, F09
University of Sydney,
(temporary email address - Nov 1990 - Feb 15, 1991 firstname.lastname@example.org)