NOMINALIZATIONS IN P U N D I T
Deborah A. Dahl, M a r t h a S. Palmer, Rebecca J. Passonneau
Paoli Research Center
UNISYS Defense Systems 1
Defense Systems, UNISYS
P.O Box 517
Paoli, P A 19301 U S A
ABSTRACT
This paper describes the t r e a t m e n t of nominalizations in the P U N D I T text processing system.
A single semantic definition is used for both nominalizations and the verbs to which they are
related, with the same semantic roles, decompositions, and selectional restrictions on the semantic
roles. However, because syntactically nominalizations are noun phrases, the processing which produces the semantic representation is different in
several respects from t h a t used for clauses. (1)
The rules relating the syntactic positions of the
constituents to the roles t h a t they can fill are
different. (2) The fact t h a t nominailzations are
untensed while clauses normally are tensed means
t h a t an alternative t r e a t m e n t of time is required
for nomlnalizations. (3) Because none of the arguments of a nominallzation is syntactically obllgatory, some differences in the control of the filling
of roles are required, in particular, roles can be
filled as part of reference resolution for the nominalization. The differences in processing are captured by allowing the semantic interpreter to
operate in two different modes, one for clauses,
and one for nominalizations. Because many nomlnalizations
are noun-noun compounds, this
approach also addresses this problem, by suggesting a way of dealing with one relatively tractable
subset of noun-noun compounds.
1. Introduction
In this paper we will discuss the analysis of
nominalizations in the P U N D I T text processing
system. 2 Syntactically, nomlnalizations are noun
phrases, as in examples (I)-(7).
(1)
An inspection of lube oil filter revealed
metal particles.
(2)
L o u of lube oll preuure occurred during
operation.
(3)
S A C received h i f h u e a f e .
(4)
In~eeti#ation revealed adequate lube oil.
(5)
Request replacement of SAC..
(6)
Erosion of impellor blade tip is evident.
(7)
Unit has low output air pressure, resulting
in ale*# gae turbine atarte.
Semantically, however, nominaliTatlons resemble
clauses, with a p r e d l c a t e / a r g u m e n t structure like
t h a t of the related verb. Our t r e a t m e n t attempts
to capture these resemblances in such a way t h a t
very little machinery is needed to analyze nominalizations other t h a n t h a t already in place for
other noun phrases and clauses.
There are two types of differences between
the t r e a t m e n t of nomlnalizatlons and t h a t of
clauses. There are those based on linqui~tle
differences, related to (1) the mapping between
syntactic arguments and semantic roles, which is
I The research described in this paper was supported in
part by DARPA under contract N000014-85-C-0012, administered by the Office of Naval Research. A P P R O V E D
FOR
1Formerly SDC-A Burroughs Company.
131
different in nomlnalisations and clauses, and (2)
tense, which nomlnallsations lack. There are also
differences in control; in particular, control of the
filling of semantic roles and control of reference
resolution. All of these issues will be discussed in
detail below.
2.
resolution from default or contextual information.
We have categorized the semantic roles into
three classes, based on how they are filled Semantic roles such as t h e m e , a c t o r and p a t i e n t are
syntactically OBLIGATORY, and must be filled by
surface constituents. Semantic roles are categorized as semantically ESSENTIAL when they must be
filled even if there is no syntactic constituent
avaUahle, s In this case they can be filled pragmatically, making use of reference resolution, as
explained below. The default categorization is
NON-ESSENTIAL, which does not require t h a t the
role be filled. The algorithm in Figure 1 produces
a semantic representation using this information.
E a c h step in the algorithm will be illustrated at
least once in the next section using the following
(typical) CASREPS text.
Clause analysis
The semantic processing to be described in
this paper is p a r t of the P U N D I T s system for
processing n a t u r a l language messages. The PUNDIT system is a highly modular system, written in
Prolog, consisting of distinct syntactic, semantic
and
discourse components.
~-lirschman1985],
and~-lirschman1986], describe the semantic components
of
PUNDIT,
while ~)ah11986, Palmer1988, Passonneau1986],
describe the semantic and pragmatic components.
The semantic domain from which these examples
are t a k e n is t h a t of reports of failures of the
starting air compressors, or s a c ' s , used in starting
gas turbines on N a v y ships.
~a© failed.
Pump sheared.
Ineestifatiort reeealed metal eontamlnation
in filter.
The goal of semantic analysis is to produce
a representation of the information conveyed by
t h e sentence, both implicit and explicit. This
involves 1) mapping the syntactic realization onto
an underlying predicate argument representation,
e.g., assigning referents of particular syntactic
consltuents to predicate arguments, and 2) mak]Jig implicit argument fillers expllclt. We are
using an algorithm for semantic interpretation
based on predicate decomposition t h a t integrates
the performance of these tasks. The integration is
driven by the goal of filling in the predicate arguments of the decomposition.~almer1986].
2.1.
A Simple
Example
D E C O M P O S E V E R B - The first example uses the
f a l l decomposition for Sac failed:
fall <beeomeP (inoperatlveP
(patlent(P))).
It indicates t h a t the e n t i t y filling the OBLIGATORY p a t i e n t role has or will become inoperative.
FOR
In order to produce a semantic representation of a clause, its verb is first decomposed into a
semantic predicate representation appropriate for
the domain. The arguments of the predicates
constitute the SEMANTIC ROLES of the verb, which
are slml]ar to cases 4 For example, fall decomposes
into b e c o m e i n o p e r a t l v e , with p a t i e n t as its
only semantic role. Semantic roles can be filled
either by a syntactic constituent or by reference
patient
ROLE
-
PROPOSE
SYNTACTIC
CONSTITUENT
FILLER - A mapping rule indicates t h a t the syntactic subject is a likely filler for any p a t i e n t
role. The mapping rules make use of intuitions
about syntactic cues for indicating semantic
roles first embodied in the notion of case
~lllmore1968,Palmer1981]. The mapping rules
can take a d v a n t a g e of general syntactic cues like
" S U B J E C T goes to P A T I E N T " while still indicating particular context sensitivities. (See ~ a l mer1985] for details.)
PUBLIC RELEASE, DISTRIBUTIONUNLIMITED.
s PUNDIT UNDderstands and Integrates Text
4 In this domain the semantic roles include: agent, Ins t i g a t o r , e x p e r i e n c e r , I n s t r u m e n t , t h e m e , Ioeatlon,
actor, p a t i e n t , source, r e f e r e n c e _ p t and goal. There
in{Paseonneau198611
s We are in the process of defining criteria for categorizing a role as ~SSeNTIAL. It is clearly very domain dependent.
domain specific criteria for selecting a range of semantic
roles. The criteria which we have used are described
are
132
CALL R E F E R E N C E R E S O L U T I O N - See is the
subject of ma© failed, and is suggested by the
mapping rule as a 1Lkely filler of the p a t i e n t role.
At this point the semantic interpreter asks noun
phrase analysis to provide a unique referent for
the noun phrase subject. Since no s a c , have been
mentioned previously, a new name is created:
sael.
T E S T S E L E C T I O N R E S T R I C T I O N S - In addition to the mapping rules t h a t are used to associate syntactic constituents with semantic roles,
there are selection restrictions associated with
each semantic role. The selection restrictions for
fail test whether or not the filler of the p a t i e n t
role is a mechanical device. A sac is a mechanical device so the subject of the sentence mac
failed maps straightforwardly onto the p a t i e n t
role,
e.g.,
beeomeP (inoper at|veP (pat|ent (sac1))).
Since there are no other roles to be filled the
algorithm term~-ates successfully at this point
and the remaining steps are not applied. The
next example illustrates further steps in the algorithm.
2.2.
Unfilled Obligatory
Roles
The second utterance in the example, P s m p
mheared, illustrates the effect of an unfilled obligatory role.
DECOMPOSE
be filled is the i n s t i g a t o r role. A mapping rule
indicates t h a t the subject of the sentence, psmp,
is a likely filler for this role. Reference resolution
returns p u m p 1
as the referent of the noun
phrase. Since pump is a mechanical device, the
selection restriction test passes.
F O R p a t i e n t R O L E - There are no syntactic
constituents left, so a syntactic constituent cannot be proposed and tested.
UNFILLED
OBLIGATORY
ROLES
- The
p a t l e n t role, a member of the set of obligatory
roles, is still unfilled. This causes failure, and the
binding of p , * r n p l to the i n s t i g a t o r
role is
undone. The algorithm starts over again, trying
to fill the instigator role.
FOR instigator
ROLE- There are no other
mapping rules for i n s t i g a t o r ,
and it is nonessential, so Case 4 applies and it is left unfilled, e
The algorithm tries again to fill in the patient
role.
F O R p a t l e n t R O L E - Two mapping rules can
apply to the p a t i e n t role, one of which suggests
the subject, in this case, the pump, as a filler.
Reference resolution returns p u m p 1 again, which
passes the selection restriction of being a mechanical device. The final representation is:
e a u s e P ( i n s t l g a t o r (I),
beeomeP (shearedP (patlent (pumpl)))).
VERB -
shear,
< - e a u s e P ( ! n s t i g a t o r (I),
beeomeP(shearedP
(patlent(P))))
Sheer is an example of a verb t h a t can be used
either transitively or intransitively. In both cases
the p a t i e n t role is filled by a mechanical device
t h a t becomes sheared. If the verb is used transitively, the i n s t i g a t o r of the shearin¢, also a
mechanical device, is mentioned explicitly, as in,
The rotating driee shaft sheared the p s m p . If
the verb is used intransitively, as in the current
example, the i n s t i g a t o r
is not made explicit;
however, the algorithm begins by attempting to
fill it in.
F O R I n s t i g a t o r R O L E - Working from left to
right in the verb decomposition, the first role to
The last sentence in the text, "Inveatlgation re~ealed metal eontaminatlon ~n filter," is
interesting mainly because of the occurrence of
two nomlnallzations which are discussed in detail
in a separate section.
2.3.
Temporal
Clauses
Analysis
of
Tensed
The temporal component determines what
kind of situation a predication denotes and what
time it is asserted to hold for ~assonneau1988].
Its input is the semantic decomposition of
the verb and its arguments, tense, an indication of whether the verb was in the perfect or
progressive, and a list of unanalyzed constituents which may include temporal adverbials. It
generates three kinds of output: an assignment of
IIn other domains, the i n s t i g a t o r might be an ~SSZN.
TLU. role and would get filled by pragmatics.
and relies heavily on w h a t can be assumed from the context.
133
an a c t u a l time to the predication, if a p p r o p r i a t e ;
a r e p r e s e n t a t i o n of the type of sRuation denoted
by the predication as either a state, a process or a
transition event; and finally, a set of predicates
a b o u t the ordering of the time of the situation
with respect to other times explicitly or implicitly
mentioned in the same sentence. For the simple
sentence, s a c / ' a i l e d , the input would consist of
the semantic decomposition and a p a s t tense
marker:
Deeomposltlons
become (|no per ative (p atlent
3Terb forms Past
(is s e l l ) ))
The o u t p u t would be a r e p r e s e n t a t i o n of a
t r a n s i t i o n a l event, corresponding to the moment
of becoming i n o p e r a t i v e , and a resulting s t a t e
in which the sac is inoperative for some period
initiating at the moment of transition.
8.
fillers, as a b y - p r o d u c t of reference resolution.
After the first pass, the i n t e r p r e t e r looks for a
referent, which, if found, will unify with the nomln a l i s a t l o n representation, sharing v a r i a b l e bindings. This is a m e t h o d of filling unfilled roles pragm a t i c a l l y t h a t is not c u r r e n t l y available to clause
analysis s. However, the first pass was i m p o r t a n t
for filling roles with a n y explicit s y n t a c t i c arguments of the nom;nalizatlon before a t t e m p t i n g to
resolve its reference, since there m a y be more
t h a n one event in the context w h k h nominallzation could be specifying. F o r example, failure of
p u m p and failure of sac can only be distinguished b y the filler of the p a t i e n t role. After
reference resolution a second role-filling pass is
m a d e , where still unfilled roles m a y be filled pragm a t i c a l l y with default values in the same w a y
t h a t unfilled v e r b roles can be filled.
S.1. Temporal
tlons
Nomlnallsatlons
Nominallzations are processed very slml]arly
to clauses, but with a few crucial d ~ e r e n c e s , b o t h
in linguistic i n f o r m a t i o n accessed and in the control of the algorithm. The first i m p o r t a n t linguistic characteristic of the nom;nallzation algorithm
is t h a t the same predicate decomposition can be
used as is used for the related verb. Secondly,
d ~ e r e n t m a p p i n g rules are required since syntactically a nominallsatlon is a noun phrase. For
example, where a likely filler for the p a t i e n t of
fail, is the s y n t a c t i c subject, a llkely filler for the
p a t i e n t of failure is an of pp. Thirdly, nominalisations do not m a k e use of the obligatory
classification for semantic roles, since
noun
phrase modifiers are not syntactically obligatory.
Analysis
of Nomlnallza-
As with clauses, the t e m p o r a l analysis of
norninallsatlons t a k e s place a f t e r the semantic
analysis. Also as with clauses, one of the inputs
to the t e m p o r a l analysis of nomlna]isatlons is the
semantic decomposition. T h e critical d ~ e r e n c e
between the two cases is t h a t a n o m ; n a l i s a t i o n
does not occur with tense. P U N D I T compensates
by looking for relevant t e m p o r a l information in
the superordinate constituents in which the nominalizatlon is embedded.
Currently, P U N D I T
processes nomlnalizatlons in three types of con°
texts.
The first context for which a nomlnalisation
is t e m p o r a l l y processed is when it occurs as the
prepositional object of a t e m p o r a l connective
(e.g., before, during, after) and the m a t r i x
clause denotes an a c t u a l situation. For example,
in the sentence sac lube oil pressure decreased
belato 60 pslg after engagement, the temporal
component processes the m a i n clause as referring
to an a c t u a l event which h a p p e n e d in the p a s t
and which resulted in a new situation. When
P U N D I T finds the t e m p o r a l a d v e r b i a l phrase
after engagement, it assumes t h a t the engagem e a t also has a c t u a l t e m p o r a l reference. In such
cases, the n o m l n a l i s a t | o n is processed using the
In t e r m s of d~rerences in control structure,
because nom;nallzations m a y themselves be anaphorlc, there are two s e p a r a t e role-filling stages in
the algorithm instead of just one. The first pass is
for filling roles which are explicitly given syntactically; essential roles are left unfilled. If a uominalization is being used anaphorically some of its
roles m a y h a v e been specified o r otherwise filled
when the event was first described. The anaphorlc reference to the event, the nomina]izatlon,
would a u t o m a t i c a l l y inherit all of these role
This suggests the hypothesis that OBLIGATORYroles For
clause decompositions automatically become BSSeNTL~ roles
for nominalization decompositions. This hypothesis seems to
hold in the current domain; however, it will have to be tested
on other domains. We are indebted to James Allen for this
observation.
! Clauses can describe previously mentioned events, as
discussed in [Dahl1987]. In order to handle cases like these,
something analogous to reference resolution for clauses may
be required. However a treatment of this has not yet been
implemented in PUNDIT.
134
the nomlnalisation metal eontamlnatlon in oll
f i l t e r with two inputs: the decomposition structure and the tense of the m a t r i x verb, in this
case the simple past. Because this predicate is
stative, the representation of the e o n t a m l n a t l o n situation is a s t a t e predicate with the
decomposition and a p e r i o d time a r g u m e n t as
well as the unique identifier S, (which will be
eventually be i n s t a n t i a t e d by reference resolution
as [ e o n t a m i n a t e l ] ) :
meaning of the adverb and the tense of the main
clause.
The second context in which a nominallzation undergoes t e m p o r a l analysis is where it
occurs as the a r g u m e n t to a verb providing temp o r a l information a b o u t situations. Such verbs
are classified as aspectual. O c c u r is such a verb,
so a sentence like failure o c c u r r e d would be processed very s~miIarly to a clause with the simple
p a s t tense of the related verb, i.e., aomethlng
state(S,
faile&
eontamlnatedP
(instrument (metall),
]oeatlon(filterl)),
(perlod(S))
Another type of verb whose nominallzation
a r g u m e n t s are t e m p o r a l l y processed is a verb
which itself denotes an a c t u a l situation t h a t is
semantically distinct from its arguments. For
example, the sentence in,aestlgatlon re~ealed
metal ¢onfam~natlon i~t oil filter mentions three
situations: the situation denoted by the m a t r i x
verb reveal, and the two situations denoted by its
arguments, ineemt~gatlon and eontamlnatlo~ If
the situation denoted by reveal has a c t u a l temporal reference, then its a r g u m e n t s are presumed
to as well.
8.2.
Nominallsatlon
In this context, the p a s t tense indicates t h a t at
least one m o m e n t within the period of c o n t a m i n a tion precedes the time at which the report was
filed.
CALL R E F E R E N C E R E S O L U T I O N F O R NOlV[INALLZATION - There are no previously mentioned ©ontamlnatlon events, so a new referent,
eontamlnatlonl
is created.
There are no
unfilled roles, so the analysis is completed.
Mapping Rules
We will Use the previous example, ineestl-
gatlon revealed metal eontamlnatlon in filter,
8.3.
to illustrate the nom~nallsation analysis algorithm.
We will describe the e o n t a m l n a t l o n
example first, since all of its roles are filled by
syntactic constituents. The dotted llne divides
the algorithm in Figure 2 in the Appendix into the
p a r t s t h a t are the same (above the line), and the
p a r t s t h a t differ (below the llne.)
The analysis of the other nominallzation,
in~emtlgatlon, illustrates how essential roles are
filled. The decomposition of i n v e s t i g a t e has two
semantic roles, a NON-ESSENTIAL a g e n t doing the
investigation and an OBLIGATORY t h e m e being
investigated. 9
(instrument
Roles
investigate
<- investlgateP
(agent (A) ~
theme(T))
D E C O M P O S E V E R B - Contaminate decomposes
into a NON-ESSENTIAL i n s t r u m e n t
that contaminates an OBLIGATORY l o e a t l o n .
eontaminate
<eontaminatedP
loeatlon(L))
Filllng Essential
There are no syntactic constituents, so the m a p ping stage is skipped, and reference resolution is
called for the nominallzatlon. There are no previously mentioned investigative events in this example 10, so a new referent, i n v e s t i g a t | o n l
is
created. At this point, a second pass is made to
a t t e m p t to fill any unfilled roles.
(I),
FOR instrument
role - In the example, m e t a l is
a noun modifier of contamination, and m e t a l l
is selected as the filler of the i n s t r u m e n t
role.
I In other domains, the t h e m e can be essential, as in "I
heard a noise. Let's investigate."
I0 If the example had been, A sew ea¢iseer isweetlgate& tAe pump. TAe isteetlgntios oeeurre~ j u s t before
tAe complete breakdown., a previously mentioned event
would have been found, and the agent and t h e m e roles
would have inherited the fillers engineer1 and p n m p l
from the reference to the previous event.
F O R t h e m e R O L E - The t h e m e of a nominaUnation can be syntactically realized by an o f pp
or an in pp. The role is filled with f l l t e r l , the
referent of/~l£er.
At this point the t e m p o r a l component is called for
135
F O R a g e n t R O L E - The role is NON-ESSENTIAL,
so Case 4 applies, and it is left unfilled.
F O R t h e m e R O L E - The selection restriction on
the t h e m e of an ineestlgation is t h a t it must be
a d * m s g e d component or a d a u a a g e causing
event. All of the events and entities mentioned so
far, the , a e and the pump, the failsre of the sac
and the s h c a r / n g of the pump satisfy this criteria. In this case, the item in focus, the ,hearing of the pump, would be selected ~)ah11986].
The final decomposition is:
investlgateP
4.
Other
cylinder of metal, have a similar analysis.
Finally, m a n y noun-noun compounds are
handled as idioms, in cases where there is no reason to analyze the semantics of their internal
structure. Idioms in the CASREPS domain include
,hip, f o r c e , gear *hair, and connecting pin.
Our decision to t r e a t these as idioms does not
imply t h a t we consider them unanalyzable, or
noncompositional, but r a t h e r t h a t , in this domain,
there is no need to analyze t h e m any further.
5.
(agent(A),theme(shearl))
Previous
Computatlonal
Treatments
Previous c o m p u t a t i o n a l t r e a t m e n t s of nominalizations differ in two ways from the current
approach. In the first place, nominallzations have
often been t r e a t e d simply as one type of nounnoun compound. This viewpoint is adopted by
~inin1980,Leonard1984,Brachman(nuli)].
Certainly m a n y nomlnalizations contain nominal
premodifiers and hence, syntactically, are nounnoun compounds; however, this approach obscures
the generalization t h a t prepositional phrase
modifiers in non-compound noun phrases often
have the same semantic roles with respect to the
head noun as noun modifiers. P U N D I T ' s analysis
is aimed at a uniform t r e a t m e n t of the semantic
s~ml]arlty among expressions like repair of
e n f l n e , enf~ne r e p a i r , and Csomeone) r e p a i r e d
englne r a t h e r t h a n the syntactic similarity of
engine repair, sir preuure, and metal partleles.
Of the
analyses
mentioned
above,
B r a c h m a n ' s analysis seems to be most similar to
ours in t h a t it provides an explicit link from the
nominalization to the related verb to relate the
roles of the noun to those of the verb. The second
way in which our approach differs from previous
approaches is t h a t P U N D I T ' s analysis is driven
by taking the semantic roles of the predicate and
trying to fill them in any way it can. This means
t h a t P U N D I T knows when a role is not explicitly
present, and consequently can call on the other
mechanisms which we have described above to fill
it in. O t h e r approaches have tended to s t a r t by
fitting the explicitly mentioned arguments into
the role slots, thus they lack this flexibility.
Compounds
In addition to nom~nalisations, P U N D I T
deals with three other types of noun-noun compounds. One is the category of nouns with arguments. These include p r e u u r e and temperature,
for example. T h e y are decomposed and have
semantic roles like nominalisations; however, their
t r e a t m e n t is different from t h a t of nomlualisations in t h a t they do not undergo time analysis,
since they do not describe temporal situations. As
an
example,
the
definition of
preuure,
pressureP (theme(T),loeation(L)),
specifies
t h e m e and l o c a t i o n as roles. The analysis of a
noun phrase like sa© oil p r e u u r e would fill in the
l o e a t l o n with the sac and the t h e m e with the
oil, resulting
in the
final representation,
pressur eP (theme(oill),loeatlon(sael)).
The syntactic mapping rules for the roles permit
the theme to be filled in by either a noun modifier,
such as all in this case, or the object of an o /
prepositional phrase, as in prcuure o / o i l . Simllarly, the mapping rules for the location allow it
to be filled in by either a noun modifier or by the
object of an in prepositional phrase. Because of
this flexibility, the noun phrases, sac all presmute, all p r e u u r e in sac, and p r e s s u r e o f oi1
i n s a c , all receive the same analysis.
The second class of compounds is t h a t of
nouns which do not have semantic roles. For
these, a set of domain-specific semantic relationships between head nouns and noun modifiers has
been developed. These include: a r e a o f o b j e c t ,
for example, blade tip, m a t e r l a l - f o r m ,
such as
metal partlclea; and m a t e r | a l - o b j e e t ,
such as
metal eyllnder. These relationships are assigned
by examining the semantic properties of the
nouns. The corresponding prepositional phrases,
as in tip o/ blade, particle, o/ metal, and
6.
L|mltat|ons
The current system has two main limitations. First, there is no a t t e m p t to build internal structure within a compound. Each nominal
modifier is assumed t o modify the head noun
unless it is p a r t of an idiom. For this reason,
136
noun phrases like impel[or blade t~p erosion
cannot be handled by our system in its current
s t a t e because impel[or b[a,le tip forms a
semantic unit and should be a n a l y s e d as a a
single a r g u m e n t of eroaion. The second problem
k related to the first. The system does not now
keep t r a c k of the relative order of nora|hal
modifiers. In this domain, this does not present
serious problems, since there are no examples
where a different order of modifiers would result
in a d ~ e r e n t analysis. Generally, only one order
is acceptable, as in mac oil eo~taminatlon, ~o~[
7.
b o t h powerful and extenslble, and which will provide a n a t u r a l basis for f u r t h e r development.
Acknowledgements
We would like to t h a n k L y n e t t e Hirschman
and Bonnie W e b b e r for their helpful c o m m m e n t s
on this paper.
Conclus|ons
In this p a p e r we have described a t r e a t m e n t
of nom~nalisatlons ill which the goal ls to maxim[se the s~m~]arities between the processing of nominallsatlons and t h a t of the clauses to w h k h they
are related. The semantic s~m~]arltles between
nom~nallzatlons and clauses are c a p t u r e d by m a k ing the semantic roles, s e m a n t k decompositions,
and selectional restrictions on the roles the same
for nomlna]isations and their related verbs. As a
result, the same s e m a n t k representation k constructed for b o t h structures. This s~m;|arity in
representation in turn anows reference resolution
to find referents for nom;nallsations w h k h refer
to events previously described in clauses. In addltion, it allows the time component to integrate
t e m p o r a l relationships a m o n g events and situations described in clauses with those referred to
by non~uaUsations.
On the other hand, where d ~ e r e n c e s
between nom~uaUsations and clauses have a clear
]ingulstic m o t i v a t i o n , our t r e a t m e n t provides for
differences in processing. P U N D I T recognizes t h a t
the semantic roles of non~na]ised verbs are
expressed syntactically as modifiers of nouns
r a t h e r t h a n a r g u m e n t s of clauses by having a
d ~ e r e n t set of syntactic m a p p i n g rules. It ls also
true in nominallsatlons t h a t there are no syntacticaUy obligatory arguments, so the analysis of a
nom;nallsation does not fall when there is an
unfilled obligatory role, as is the case with clauses.
Finally, the t e m p o r a l analysis component is able
to t a k e into account the fact t h a t nomlnallzatlons
are untensed.
~rh;le there are m a n y cases not yet covered
by our system, in general, we believe this to be an
a p p r o a c h to processing nomlnallsatlons which is
137
APPENDIX
DECOMPOSE VERB;
FOR EACH SEMANTIC ROLE
C A S E I: IF T H E R E A R E S Y N T A C T I C C O N S T I T U E N T S
P R O P O S E S Y N T A C T I C C O N S T I T U E N T FILLER
CALL REFERENCE RESOLUTION
-
& TEST SELECTIONAL RESTRICTIONS
C A S E 2: IF R O L E IS O B L I G A T O R Y
FAIL
AND SYNTACTICALLY UNFILLED
C A S E 3: IF R O L E IS E S S E N T I A L A N D U N F I L L E D C A L L R E F E R E N C E R E S O L U T I O N T O H Y P O T H E S I Z E A FILLER
& TEST SELECTIONAL RESTRICTIONS
C A S E 4: IF R O L E IS N O N - E S S E N T I A L A N D U N F I L L E D LEAVE UNFILLED
CALL TEMPORAL
ANALYSIS ON DECOMPOSITION
FIKure 1. C l a u s e AJtalysls AlKorlChm
DECOMPOSE NOMINALIZATION
F O R E A C H S E M A N T I C ROLE:
IF THERE ARE SYNTACTIC CONSTITUENTS PROPOSE SYNTACTIC CONSTITUENT FILLER
& CALL REFERENCE RESOLUTION
& TEST SELECTIONAL RESTRICTIONS
CALL TEMPORAL ANALYSIS ON DECOMPOSITION
CALL REFERENCE RESOLUTION FOR NOMINALIZATION NOUN PHRASE
FOR EACH SEMANTIC ROLE:
IF ESSENTIAL ROLE AND UNFILLED
CALL REFERENCE RESOLUTION TO HYPOTHESIZE A FILLER
TEST SELECTIONAL RESTRICTIONS
ELSE LEAVE UNFILLED
FJKure 2. N o m l n a l l s a ~ i o n A n a l y s i s AIKorlthm
138
-
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