Extraposition via Complex Domain Formation* 
Andreas Kathol and Carl Pollard 
Dept. of Linguistics 
, 1712 Neil Ave. 
Ohio State University 
Columbus, OH 43210, USA 
{kathol, pollard}©ling, ohio-stat e. edu 
Abstract 
We propose a novel approach to extraposi- 
tion in German within an alternative con- 
ception of syntax in which syntactic struc- 
ture and linear order are mediated not via 
encodings of hierarchical relations but in- 
stead via order domains. At the heart of 
our proposal is a new kind of domain for- 
mation which affords analyses of extrapo- 
sition constructions that are linguistically 
more adequate than those previously sug- 
gested in the literature. 
1 Linearization without phrase 
structure 
Recent years have seen proposals for the elimina- 
tion of the phrase structure component in syntax in 
favor of levels of representation encompassing possi- 
bly nonconcatenative modes of serialization (Dowty, 
In press; Reape, 1993; Reape, 1994; Pollard et al., 
1993). Instead of deriving the string representation 
from the yield of the tree encoding the syntactic 
structure of that sentence (as, for instance in GPSG, 
LFG, and--as far as the relationship between S- 
structure and PF, discounting operations at PF, is 
concerned--GB), these proposals suggest deriving 
the sentential string via a recursive process that op- 
erates directly on encodings of the constituent order 
of the subconstituents of the sentence. In Reape's 
proposal, which constitutes an extension of HPSG 
(Pollard and Sag, 1994), this information is con- 
tained in "(Word) Order Domains". On the other 
hand, the way that the surface representation is put 
together, i.e. the categories that have contributed 
to the ultimate string and the grammatical depen- 
dency relations (head-argument, head-adjunct, etc.) 
holding among them, will be called the "composi- 
tion structure" of that sentence, represented below 
by means of unordered trees. 
*Thanks to Bob Kasper for helpful discussions and 
suggestions. 
As an example, consider how a German V1 sen- 
tence, e.g. a question or conditional clause, is derived 
in such a system. 1 
(1) Las Karl dasBuch 
read Karl the book 
E.g.: 'Did Karl read the book?' 
The representation in Figure 1 involves a number 
of order domains along the head projection of the 
clause (\[1\]-\[3\]). Each time two categories are com- 
bined, a new domain is formed from the domains 
of the daughters of that node, given as a list value 
for the feature DOM. While the nodes in the deriva- 
tion correspond to signs in the HPSG sort hierarchy 
(Pollard and Sag, 1994), the elements in the order 
domains, which we will refer to as domain objects, 
will minimally contain categorial and phonological 
information (the latter given in italics within angled 
brackets). The value of the DOM attribute thus con- 
sists of a list of domain objects. Ordering is achieved 
via linear precedence (LP) statements. 
In Reape's approach, there are in essence two ways 
in which a sign's DOM value can be integrated into 
that of its mother. When combining with its ver- 
bal head, a nominal argument such as das Buch in 
Figure 1 in general gives rise to a single domain ele- 
ment, which is "opaque" in the sense that adjacency 
relations holding within it cannot be disturbed by 
subsequent intervention of other domain objects. In 
contrast, some constituents contribute the contents 
of their order domains wholesale into the mother's 
domain. Thus, in Figure 1, both elements of the VP 
(\[2\]) domain become part of the higher clausal (\[1\]) 
domain. As a result, order domains allow elements 
that are not sisters in composition structure to be 
linearly ordered with respect to each other, contrary 
1In Kathol and Pollard (1995), we argue for dispens- 
ing with binary-valued features such as INV(ERTED) or 
EXTRA(POSED) in favor of a multi-valued single feature 
TOPO(LOGY) which imposes a partition on the set of do- 
main elements of a clause according to membership in 
Topological Fields (see also Kathol (In progress)). Since 
nothing in the present proposal hinges on this detail, we 
keep with the more common binary features. 
174 
\[1\] I 
S -- V\[SUBCAT O\] 
DOM/ \[ (las) \] (Karl) \ Lv\[+'NV\] \] \[ \] ' NP\[NOM\] ' ( das Buch) 
rNP\[NOM\] 
\[4\] \[DOM (\[(KarO\]) \] 
= V\[SUBCAT (NP\[NOM\])\] 1 
\[2\] /DOM/ \[("as) 1 ru,,., B,.,ch)\] \/ L \ 
Lv\[-FINV\]j ' t NP\[ACC\] \] /J 
,. . . ~ rVrSUB¢~T~'--T~rNO~I, ',,,,,,c,,,,,l 
,3, \]} 
Figure h Derivation of V1 clause using order domains 
NP\[ACC\])\] 
to ordinary HPSG, but in the spirit of "liberation" 
metarules (Zwicky, 1986). 
With Reape we assume that one crucial mecha- 
nism in the second type of order domain formation is 
the shuffle relation (Reape's sequence union), which 
holds of n lists L1, ..., L,-1, L,, iff L, consists of 
the elements of the first n-1 lists interleaved in such a 
way that the relative order among the original mem- 
bers of L1 through L,-1, respectively, is preserved in Ln. 
As a consequence, any precedence (but not ad- 
jacency) relations holding of domain elements in one 
domain are also required to hold of those elements 
in all other order domains that they are members 
of, which amounts to a monotonicity constraint on 
deriving linear order. Hence, if \[1\] in Figure 1 were 
to be expanded in the subsequent derivation into 
a larger domain (for instance by the addition of a 
sentential adverb), the relative order of subject and 
object in that domain could not be reversed within 
the new domain. 
The data structure proposed for domains in 
Reape (1993) is that of a list of objects of type sign. 
However, it has been argued (Pollard et al., 1993) 
that signs contain more information than is desirable 
for elements of a domain. Thus, a sign encodes its 
internal composition structure via its DAUGHTERS 
attribute, while its linear composition is available as 
the value of DOM. Yet, there are no known LP con- 
straints in any language that make reference to these 
types of information. We therefore propose an im- 
poverished data structure for elements of order do- 
mains which only consists of categorial and seman- 
tic information (viz. the value of SYNSEM (Pollard 
and Sag, 1994)) and a phonological representation. 
This means that whenever a constituent is addedto 
a domain as a single element, its information con- 
tent will be condensed to categorial and phonolog- 
ical information. 2 The latter is constrained to be 
the concatenation of the PHONOLOGY values of the 
domain elements in the corresponding sign's order 
2For expository convenience, semantic information is 
systematically ignored in this paper. 
domain. We will refer to the relation between a sign 
S and its representation as a single domain object 
O as the compaction, given informally in (2): 3 
(2) compaction(\[i-\],El ) -- 
rsig. \] 53:/sYNSZM if\] 
LD°" (\[PHON \[ 4.~\],...,\[PHON\[~) 
\[ dom-obj \] 
A ~: I s,,N~E~,~I~ LPHONI,Io ... o r-;-I 
To express this more formally, let us now define an 
auxiliary relation, joinF, which holds of two lists 
L1 and L2 only if L2 is the concatenation of val- 
ues for the feature F of the elements in L1 in the 
same order: 4 
(3) joinF(\[Y\],\[~) -- 
(V\]: 0 A \[7\]: O) 
V (cons(IF (El)\], \[-~-\],\[~ 
A joinF(\[?\],\[~) 
A append(\[';'\],r~,\[~\]) ) 
This allows us to define compaction more precisely 
as in (4): 
(4) compaction(\[-i-\],\[~) _--- 
\[sign \] ~:/sYNSEM ~/ 
LDOM~ J 
r dom-obj \] ^ 
~: I SYNSE~,~-..I~I LPHON sL~ .\] 
A joinp//oN (\[7\],\[~) 
3Here, "o" is a convenient functional notation for the 
append relation. 
4Here cons is the relational analogue of the LISP 
function cons; i.e. cons holds among some element E 
and two lists L1 and L2 only if the insertion of E at the 
beginning of L1 yields L2. 
175 
VP "-" V\[SUBCAT (NP)\] \] 
I  r/,zasBuch)\] >\] DoM j 
L D°M (\[(das)\], \[(Buch)\])\] \[DOM~( \[V\[+,NV\] \] > 
A compaction(\[~\],\[~\]) 
^ shuffle(q , E\], \[D 
Figure 2: Domain formation using compaction and shuffle 
Given compaction and the earlier shnffle relation, 
the construction of the intermediate VP domain can 
be thought of as involving an instance of the Head- 
Complement Schema (Pollard and Sag, 1994), aug- 
mented with the relevant relational constraints on 
domain formation, as shown in Figure 2. 
2 Extraposition via Order Domains 
Order domains provide a natural framework for or- 
der variation and discontinuous constituency. One of 
the areas in which this approach has found a natural 
application is extraposition of various kinds of con- 
stituents. Reape (1994) proposes the binary-valued 
feature EXTRA to order an extraposed VP last in the 
domain of the clause, using the LP statement in (5): 
(5) \[--EXTRA\] "~ \[+EXTRA\] 
Similarly, Nerbonne (1994) uses this feature to 
account for instance for extrapositions of relative 
clauses from NPs such as (6); the composition struc- 
ture proposed by Nerbonne for (6)is given in Fig- 
ure 3. (6) 
einen Hund fiittern \[der Hunger hat\] 
a dog feed that hunger has 
'feed a dog that is hungry' 
The structure in Figure 3 also illustrates the fea- 
ture UNIONED, which Reape and Nerbonne assume 
to play a role in domain formation process. Thus, a 
constituent marked \[UNIONED -Jr-\] requires that the 
contents of its domain be shuffled into the domain 
of a higher constituent that it becomes part of (i.e. 
it is domain-unioned). For instance, in Figure 3, the 
\[UNIONED +\] specification on the higher NP occa- 
sions the VP domain to comprise not only the verb, 
but also both domain objects of the NP. Conversely, 
a \[UNIONED --\] marking in Reape's and Nerbonne's 
system effects the insertion of a single domain ob- 
ject, corresponding to the constituent thus specified. 
Therefore, in Figure 3, the internal structure of the 
relative clause domain becomes opaque once it be- 
comes part of the higher NP domain. 
3 Shortcomings of Nerbonne's 
analysis 
One problematic aspect of Nerbonne's proposal con- 
cerns the fact that on his account, the extraposabil- 
ity of relative clauses is directly linked to the Head- 
Adjunct Schema that inter alia licenses the combi- 
nation of nominals with relative clauses. However, 
whether a clause can be extraposed is independent 
of its adjunct/complement status within the NP. 
Thus, (7) illdstrates the extraposition of a comple- 
ment clause (Keller, 1994): 
(7) Planck hat die Entdeckung gemacht 
Planck has the discovery made 
\[dab Licht Teilchennatur hat\]. 
that light particle.nature has 
'Planck made the discovery 
that light has a particle nature.' 
The same also holds for other kinds of extraposable 
constituents, such as VPs and PPs. On Nerbonne's 
analysis, the extraposability of complements has to 
be encoded separately in the schema that licenses 
head-complement structures. This misses the gen- 
eralization that extraposability of some element is 
tied directly to the final occurrence within the con- 
stituent it is dislocated from. s Therefore, extrapos- 
ability should be tied to the linear properties of the 
constituent in question, not to its grammatical func- 
tion. 
A different kind of problem arises in the case of ex- 
tractions from prepositional phrases, as for instance 
in (S): 
(8) an einen Hund denken \[der Hunger hat\] 
of a dog think that hunger has 
'think of a dog that is hungry' 
On the one hand, there has to be a domain object for 
an einen Hund in the clausal domain because this 
SNote that final occurrence is a necessary, but 
not sufficient condition. As is noted for instance in 
Keller (1994), NP complements (e.g. postnominal geni- 
tives) cannot be extraposed out of NPs despite their final 
occurrence. We attribute this fact to a general constraint 
against extraposed NPs in clauses, except for adverbial 
accusative NPs denoting time intervals. 
176 
VP oo.( <.r \], \], )\] 
~_. I r (einen Hund) \] \[ ( der Hunger hat)| \] 
"REL-S 
UNIONED - \[NP \] EXTRA"~- 
DoM (\[ (eine.)1, \[(Hund) \]) ool,,, ( \[<Jet)\] <Hunger) 
. \],\[<v',O,>\]) 
Figure 3: Extraposition of relative clause in Nerbonne 1994 
\[VoM 
element is subject to the same variations in linear 
order as PPs in general. On the other hand, the 
attachment site of the preposition will have to be 
higher than the relative clause because clearly, the 
relative clause modifies the nominal, but not the PP. 
As a potential solution one may propose to have 
the preposition directly be "integrated" (phonologi- 
cally and in terms of SYNSEM information) into the 
NP domain object corresponding to einen Hund. 
However, this would violate an implicit assumption 
made in order domain-based approaches to lineariza- 
tion to the effect that domain objects are inalterable. 
Hence, the only legitimate operations involve adding 
elements to an order domain or compacting that do- 
main to form a new domain object, but crucially, op- 
erations that nonmonotonically change existing do- 
main objects within a domain are prohibited. 
4 Partial compaction 
In this section, we present an alternative to Ner- 
bonne's analysis based on an extension of the pos- 
sibilities for domain formation. In particular, we 
propose that besides total compaction and domain 
union, there is a third possibility, which we will call partial compaction. 
In fact, as will become clear be- 
low, total compaction and partial compatcion are 
not distinct possibilities; rather, the former is a sub- 
case of the latter. 
Intuitively, partial compaction allows designated 
domain objects to be "liberated" into a higher do- 
main, while the remaining elements of the source 
domain are compacted into a single domain object. 
To see how this improves the analysis of extraposi- 
tion, consider the alternative analysis for the exam- 
ple in (6), given in Figure 4. 
As shown in Figure 4, we assume that the or- 
der domain within NPs (or PPs) is essentially flat, 
and moreover, that domain objects for NP-internal 
prenominal constituents are prepended to the do- 
main of the nominal projection so that the linear 
string is isomorphic to the yield of the usual right- 
branching analysis trees for NPs. Adjuncts and 
complements, on the other hand, follow the nomi- 
nal head by virtue of their \["t-EXTRA\] specification, 
which also renders them extraposable. If the NP 
combines with a verbal head, it may be partially 
compacted. In that case, the relative clause's do- 
main object (El) is inserted into the domain of the 
VP together with the domain object consisting of 
the same SYNSEM value as the original NP and that 
NP's phonology minus the phonology of the relative 
clause (\[~\]). By virtue of its \[EXTRA "~-\] marking, the 
domain object of the relative clause is now ordered 
last in the higher VP domain, while the remnant NP 
is ordered along the same lines as NPs in general. 
One important aspect to note is that on this ap- 
proach, the inalterability condition on domain ob- 
jects is not violated. Thus, the domain object of 
the relative clause (\[~ in the NP domain is token- 
identical to the one in the VP domain. Moreover, 
the integrity of the remaining NP's domain object 
is not affected as--unlike in Nerbonne's analysis-- 
there is no corresponding domain object in the do- 
main of the NP before the latter is licensed as the 
complement of the verb fattern. 
In order to allow for the possibility of partially 
compacting a domain by replacing the compaction 
relation of (4) by the p-compaction relation, which 
is defined as follows: 
177 
I VP , IZ\]/REL-~ L EXTRA -4- 
\[\] /r,e,ne.,\] \] r' er  n,erha"\] 
 DET 
\[~oM (\[(#,,n~)\])\] 
^ p-compaction(l-i-l,\[Z\], lID) 
^ shume(I\[Zl), (~,l'q,~ 
I REL-S 
EXTRA + 
v,.\ LR~.'. J' uP \[,:.')\])\] 
Figure 4: Extraposition via partial compaction 
(9) p-compaction (\[~\],\[~\],\[~) -- 
\[ sign "1 
LDOMIZ\] J 
\[ dora-oh1 \] 
^ \[~: 1~_5\]1 \[PHON 7LT.J J 
^ shume(m,\[\],~ 
A joineHoN (~J,\[L\]) 
Intuitively, the p-compaction relation holds of a sign 
S (~\]), domain object O (\[~, and a list of domain 
objects L (~\]) only if O is t~-e compaction of S with 
L being a llst of domain objects "liberated" from 
the S's order domain. This relation is invoked for 
instance by the schema combining a head (H) with 
a complement (C): 
(10) \[i~\] 
\[I-I:\] \[DOMF~ \] \[C:\] \[\] 
A p- compaction (\[~\],~\],\[~\]) 
^ shume((\[~,ff\],\[E,ff\]) 
^ \[B: zist ( \[s~NSEM \[EXTRA +\]\]) 
\[ \[ HEAD verb ^(\[\]: <> v \[ :LS'N EM-Lsu. AT <>\]\]) 
The third constraint associated with the Head- 
Complement Schema ensures that only those ele- 
ments that are marked as \[EXTRA -t-\]) within the 
smaller constituent can be passed into the higher do- 
main, while the last one prevents extraposition out 
of clauses (cf. Ross' Right Roof Constraint (Ross, 
1967)). 
This approach is superior to Nerhonne's, as the 
extraposability of an item is correlated onlywith 
its linear properties (right-peripheral occurrence in 
a domain via \[EXTRA +\]), but not with its sta- 
tus as adjunct or complement. Our approach also 
makes the correct prediction that extraposition is 
only possible if the extraposed element is already 
final in the extraposition source. 6 In this sense, ex- 
traposition is subject to a monotonicity condition to 
the effect that the element in question has to occur 
in the same linear relationship in the smaller and 
the larger domains, viz. right-peripherally (modulo 
other extraposed constituents). This aspect clearly 
favors our approach over alternative proposals that 
treat extraposition in terms of a NONLOCAL depen- 
dency (Keller, 1994). In approaches of that kind, 
there is nothing, for example, to block extraposition 
of prenominal elements. 
Our approach allows an obvious extension to the 
case of extraposition from PPs which are prob- 
lematic for Nerbonne's analysis. Prepositions are 
prepended to the domain of NPs in the same way 
6It should be pointed out that we do not make the as- 
sumption, often made in transformational grammar, that 
cases in which a complement (of a verb) can only occur 
extraposed necessitates the existence of an underlying 
non-extraposed structure that is never overtly realized. 
178 
Iv. )\] DOM\[5-'\]i \[\]\[ (Neienen Hund der ftunger hai) \], \[ (vf£Ltteru) \] 
\] \[ (einen) \[\] DoM T , 
A p-compaction(I-F\],\[\], 0) 
^ shutne((\[~,0 ,\[\],El) 
Figure 5: Total compaction as a special case of compaction 
that determiners are to N domains. 
Along similar lines, note that extrapositions from 
topicalized constituents, noted by Nerbonne as a 
challenge for his proposal, do not pose a problem 
for our account. 
(11) Eine Dame ist an der Tiir 
a lady is at the door 
\[die Sie sprechen will\]. 
who you speak wants 
'A lady is at the door 
who wants to talk to you.' 
If we assume, following Kathol (In progress), that 
topicalized constituents are part of the same clausal 
domain as the rest of the sentence, 7 then an ex- 
traposed domain object, inherited via partial com- 
paction from the topic, will automatically have to 
occur clause-finally, just as in the case of extraposi- 
tion from regular complements. 
So far, we have only considered the case in which 
the extraposed constituent is inherited by the higher 
order domain. However, the definition of the p- 
compaction relation in (12) also holds in the case 
where the list of liberated domain objects is empty, 
which amounts to the total compaction of the sign 
in question. As a result, we can regard total com- 
paction as a special case of the p-compaction relation 
in general. This means that as an alternative lin- 
earization of (6), we can also have the extraposition- 
less analysis in Figure 5. 
Therefore, there is no longer a need for the 
UNIONED feature for extraposition. This means that 
we can have a stronger theory as constraints on ex- 
traposability will be result of general conditions on 
the syntactic licensing schema (e.g. the Right Roof 
Constraint in (10)). But this means that whether or 
not something can be extraposed has been rendered 
exempt from lexical variation in principle---unlike in 
Reape's system where extraposability is a matter of 
lexical selection. 
rI.e. the initial placement of a preverbal constituent in 
a verb-second clause is a consequence of LP constraints 
within a flat clausal order domain. 
Moreover, while Reape employs this feature for 
the linearization of nonfinite complementation, it 
can be shown that the Argument Composition 
approach of Hinrichs & Nakazawa (Hinrichs and 
Nakazawa, 1994), among many others, is linguisti- 
cally superior (Kathol, In progress). As a result, we 
can dispense with the UNIONED feature altogether 
and instead derive linearization conditions from gen- 
eral principles of syntactic combination that are not 
subject to lexical variation. 
5 Conclusion 
We have argued for an approach to extraposition 
from smaller constituents that pays specific atten- 
tion to the linear properties of the extraposition 
source, s To this end, we have proposed a more fine- 
grained typology of ways in which an order domain 
can be formed from smaller constituents. Crucially, 
we use relational constraints to define the interde- 
pendencies; hence our approach fits squarely into the 
paradigm in which grammars are viewed as sets of 
relational dependencies that has been advocated for 
instance in DSrre et al. (1992). Since the relational 
perspective also lies at the heart of computational 
formalisms such as CUF (DSrre and Eisele, 1991), 
the ideas presented here are expected to carry over 
into practical systems rather straightforwardly. We 
leave this task for future work. 

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