PROLOG-REQUEST@SUSHI.STANFORD.EDU (Chuck Restivo, The Moderator) (07/27/87)
PROLOG Digest Monday, 27 Jul 1987 Volume 5 : Issue 48
Today's Topics:
Query - Blackboard Architectures & CHAT
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Date: Wed 22 Jul 87 11:52:28-CDT
From: Olivier J. Winghart <CS.WINGHART@R20.UTEXAS.EDU>
Subject: Blackboard architectures in Prolog
I am looking for natural ways of implementing a blackboard
architecture in Prolog. Has anyone already thought about this, and are
there any papers that I could look at ? I would appreciate any
pointer.
-- Olivier
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Date: Mon, 20 Jul 87 13:48 EDT
From: McHale@RADC-MULTICS.ARPA
Subject: Help with CHAT
We are working with topographical maps that have information such as
towns, rivers, airports, railroads, roads, dams, bridges,... This has
us looking at a much finer grain data base than CHAT did. We modified
the template file for the resulting new semantic hierarchy.
We originally intended to extend CHAT to handle pronomial references,
ellipsis, etc. however, we ran into trouble just handling conjunctions
and adjectives. The query 'is Tokyo european?' is answered 'yes'. This
may be a problem with my converting from Dec-10 prolog to Quintus, but
I don't think so. We fixed the grammar for this particular problem,
(the only change we've made to the grammar) but the system doesn't handle
it correctly later on (in Clausify).
I'll send you a more detailed outline of changes we've made. Another
thing that I would like to know more about is the ND table. I know it is
important for query optimization but have no idea on how to select proper
values for it.
We'd appreciate any pointers you can give.
-- Mike
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Date: Mon, 20 Jul 87 15:30:52 EDT
From: mchalem@radc-lonex.arpa
Subject: CHAT
Chat-80 is a PROLOG-based front-end natural language interface to
a worldwide database. It was written in partial fulfillment of
Fernando Pereira's PhD. thesis at the University of Edinburgh for the
degree of Doctor of Philosophy in Artificial Intelligence. Michael
McHale, John Crowter, and Mary Ann Huntley of RADC are working in
conjunction with Dr. Richard Kittredge, a linguist from the University
of Montreal and the Odyssey Research Corporation in Ithaca, to extend
Chat-80.
The worldwide database has been replaced with the database
Michael Hilton is using for his simulation, and includes parts of West
Germany, East Germany, and Czechoslovakia. Scott Gregory wrote LISP
routines which convert the database from ASCII to PROLOG. It is hoped
that the modified Chat will serve as the natural language interface to
the aforementioned simulation.
Chat-80 takes as input a natural language query, such as, What is
the capital of the United States. The query is first syntactically
parsed, and categorized as being one of four basic types of queries:
declarative, yes/no, wh-type, or imperative. This parse is then sent
off to semantics, where it encounters query planning and then query
evaluation. In this (not so well understood) stage of processing, the
query is mathematically optimized such that the most efficient access
to the database is performed. The database is then searched for the
answer, which is printed.
Modifications to CHAT-80
Many people suggested that Chat-80's grammar should be changed as
little as possible due to its extreme complexity and nice
organization. We therefore have been extensively modifying the
lexicon. In addition to addding new words, we have added a clever
feature to handle verbs. Previously, to add a verb and all its
tenses, six new entries had to be added to the lexicon. Now we have a
rule whereby we add the verb in only two places, and the tenses of the
verb are automatically created and added to the lexicon. It is also
necessary to modify the semantic dictionary, as well as the domain
dependent rule base when adding a new item to the syntactic
dictionary. It is interesting to note that although a complete
syntactic parse is made before entering semantic interpretation of the
input, some key words are coded directly into the grammar, i.e.,
wh-terms: where and what.
Preprocessing
In an effort to utilize as much of Chat-80 as possible without
changing the grammar, we decided to preprocess the input query. In
this way, we massage the query into one which Chat-80 (hopefully)
understands and can answer. The preprocessor contains several steps
in accordance with several problems we have encountered:
Imperatives
We want to be able to handle imperatives, such as Show me road
7, and Please show me the railroads. (This is with the intent that
Jean Carletta's graphics routines will be utilized. When the user
asks to see the railroads, for instance, the railroads on the screen
will be highlighted.) We thus look at the input query, and try to
match the beginning of the query with the three types of imperatives
our system can handle: show, show me, and please show me. Upon
finding that the input starts with one of these three phrases, the
query is transformed into one of the form: Where is ..., and this new
query is handed to Chat, as if it were the original query.
Compound words
Compound words such as Erfurt_North (anything with an underscore in
it) and type one, type two, and type three (words which have a special
meaning when used together) posed another problem. We have made it
possible to type a compound word as either having an underscore or not.
Also, type one, type two, and type three now are treated as a single
entity. Compound nouns were also problematic; i.e., road 7, where both
road and 7 are considered nouns. We have enabled the grammar to handle
double nouns by classifying them as a special type of compound word.
Synonyms
We wanted equivalent words to have equivalent meanings. Ergo, we
have made the following synonyms in our system:
waterway = river = stream = brook = creek
town = city
road = roadway = route
Spelling Checker
Due to the complexity of the spelling of the proper nouns in the
database, as well as the human error of misspellings and typographical
errors, a pattern matching spelling checker is implemented. If a word
in the input is not in the dictionary, then the user is informed, the
closest match replaces the unknown word, and the query proceeds as
usual.
"What is proper noun" query
It is helpful for the user to ask the system, for example,
What is Apolda. The system should then reply a town. However, the
response supplied by Chat was Apolda. Similarly, when asked what 7
was, the system replied 7, when what was intended was a road. We thus
needed a way to solve this problem. Our solution was to turn to the
preprocessor, which will look at the input query, and determine if it
is of the form "What is proper noun." If it is, then we check to see
what kind of thing the proper noun is during the logic phase of the
query processing.
Single noun phrase queries
It is desirous to have the ability to input a single noun
phrase such as Merseburg or road 7, and have Jean's system highlight
the appropriate area on the map. Thus, we needed to be able to parse
single noun phrases. Again we turned to the preprocessor to solve
this problem. If the input query contains a single noun phrase, then
we transform it to the form: "Where is np," and the process proceedes
as usual.
semantic hierarchy
We found it necessary to change the semantic hierarchy in
accordance with the information in the specialized database with which
we are working. The new hierarchy is as follows:
feature
area point line
block town land water
country heliport
terrain bridge
wetland dam road river
mountain obstruction railroad
airstrip power line
border
Test file
A test file was created which contains several queries which
currently work on our system. This was added so that whenever we add
a new feature to the system, we can execute this file to see if the
modification creates errors elsewhere.
Help file
David Warhoftig has created a help file to orient new users to the
system. It is composed of three parts:
Welcome for new users
This introduces the user to Chat; i.e., what it is, what it does, and
how to use it.
Sample queries and responses
Similar to the module in Chat-80, this facility aids the user in
formulating a query which the system can understand.
Helpful hints and reminders
Suggestions are offered on how to represent the input; i.e.,
the user is informed that the query need not start with a capital
letter, nor does it need to end with a question mark. Also, commas in
the input are ignored, and a spelling checker is implemented.
Current problems
Distance
We are currently examining distance queries, such as 'How far is Goslar
from Merseburg', and 'What is the distance between Apolda and Artern'.
Jean Carletta has written LISP routines to compute distances, and we will
either use them or modify them to suit our needs. In either case, they
must be translated to Prolog.
Pronomial Reference
We would like for the user to be able to use pronouns, and have them
refer to the response from the previous query.
Difficulty with adjectives
We have found particular difficulty in adding adjectives to Chat-80. We
feel that the implementation of adjectives may be somewhat weak, as when
we asked the original Chat-80 if Tokyo is European, the reply was 'yes'. We
would like to have the capacity to ask queries involving the adjective
mountainous.
Remarks
In light of the fact that a great deal of effort was expended to gain an
overall feel for the code, we feel that we have been making steady progress
in modifying Chat-80.
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End of PROLOG Digest
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