\]'he Commercial Application of 
Natural Language \[nLerfaces 
Harry Tennant 
Computer Sciunee Center 
Texas insLruments 
Dallas, Texas 
! don't think that natural language 
interffaces are a very good idea. By that \[ 
mean conventional natural language 
interfaces -- the kind where the user" types 
in a question and the system tries to 
understand it. Oh sure, when (if?) 
computers have world knowledge th,'~t is 
comparable to what humans need to 
communicate with eactr other, natural 
language interfaces will be easy to build 
and, depending on what else is available, 
might be a good way to communicate with 
computers. But today we are soooooo fat 
away from having that much knowledge in a 
system, conventional natural language 
interfaces don't make sense. 
There is something different that makes 
more sense ---- NLMenu. It is a combination 
of menu technology with natural language 
understanding technology, and it e\]iminates 
many of the deficiencies one finds with 
conventional natural language interfaces 
while retaining the important benefits. 
~ince a eonvewLional natural language 
interface invites the user" to type in 
whatever he wants, it is based on the 
assumption that it will be able to 
understand just about anything that the 
users are likely to say. All systems today 
deal with limited domains of: discourse. I 
am convinced that users are likely to type 
in al\] kinds of things. The probability is 
high that users will not be understood. 
They eou\]d be taught the limitations of 
linguistic and concepLu~\] coverage of the 
system, but: a major motivation of building 
naJtural language interfaces is t:o allow 
effective use without t~'aining or 
retraining. So, it doesn't seem like a 
very good idea. 
The assumption behind NLMenu is the 
opposite. It assumes that there are ali 
kinds of th~ngs that the users would like 
to ask but that the coverage is so limited 
that i£ is best to reveal the coverage 
(limitations) to the user'. He then (:an 
find quickly that what he wanted £o ask 
cannot be asked of this system, so he'll 
give up quickly, minimizing his 
frustration. Or he might find that what he 
wanted to ask can be asked and the system 
helps him ,ask it in the way it will 
understand. There is another importarrL 
advantage: there may be things that the 
user did not imagine that he could ask 
about. NLMenu revea\]s these to the user 
encouraging him to make full use of sysLem 
capabilities, Conventional natural 
language systems do not. 
NLNenu works by displaying a collection of 
menus of words and phrases on the screen. 
The user builds sentences by selecting 
words and phrases from the menus. \]-he 
menus are driven by a parallel parser which 
maintains all parses of the sentence 
fragment constructed so far. AFter each 
word or phrase is selected, the parser 
looks ahead in the grammar for all the 
phrases that could come next for each 
parse. A new set of menus is constructed 
with these phrases, which are then 
displayed £o the user for his next 
selection. In this way, the NLHenu system 
is constraining the user to constructing 
only those ,'{ententes that are parsabie with 
the grammar. By including semantic 
constraints, one can also constrain the 
user to the conceptual coverage o¢ the 
system. In our" current implementations, we 
use semantic grammars so syntactic and 
semantic constraints are conveyed simply. 
Many other techniques can be imagined. 
Because the NLMenu technique rests on the 
same technologies as conventional natural 
language interfaces, they have 'Lhe same 
expressive power --- one can say the same 
range of things with either approach. But 
since NLMenu is a system-initiated dialog, 
the system always knows what the user is 
trying to express. This makes it very easy 
to mix natural lanquage (sentence building) 
with other- interface techniques such as 
graphical input, forrn fi\] ling and others. 
For" example, in an application involving 
airports, when the user was about to enter 
the location, a map popped up, the user 
pointed at the area of interest, then the 
map went away and the coordinates of that 
\]oeation were textually inserted into the 
sentence. The user then continued building 
the sentence. This allowed the use of text 
where appropriate (specifying runway 
lengths, location names, e~c.) and graphics 
where appropriate (specifying locations). 
It .seems £o me that there is much more that 
user interfaces ~-an gain from natural 
language research. For exeJmple, 
cooperative response is a good idea 
independent of whether an original query 
was expressed in English or a formal query 
language or through some other means. 
Similarly, repeated reference is important 
in any extended dialog. Discourse objects 
should remain available for terse 
reference. There is nothing that limits 
repeated reference to natura\] language 
dia\]ogs. Ideas based on focus and dialog 
s~ruct:ure can be app\]ied to dia\]ogs 
mediated throu!\]h all sorts of interface 
languages. We seem to be concentrating on 
reproducing the form of human communication 
and ignoring the substance: large 
vocabularies, concept creation through 
reference, modificaJtion and analogy, 
mechanisms I:hat use context to gain 
terseness and allowing dia\]ogs to 
accomodate the nonlir~ear characteristics of 
human thought. Natural \]anguage researc\]h 
has much more Lo offer" the world than 
simply a means for interpreting typewritten 
commands, yet we as a field have 
accomplished little toward influencing the 
other user interface technologies. 
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