AN ATN TREATMENT WH-MOVEMENT 
Hans Haugeneder 
Siemens A G 
ZT ZTI 
Otto.Hahn.Ring 6 
8 Mfinchen 83, West Germany 
ABSTRACT 
An ATN-Parser is presented with emphasis on 
the treatment of those phenomena which in the 
framework of transformational grammar are sub- 
sumed under the concept of WH-movement. The 
approach taken tries to embed these constructions 
into an ATN grsmmar in a general, linguistically 
motivated and in terms of the ATN gr~mrn~r 
formalism descriptive way. To accomplish this goal 
the approach described incorporates the basic 
principles governing such constructions as 
formulated in the framework of the trace theory 
roposed in the development of the Extended 
tandard Theory (EST). Thus a ,miffed treatment 
for both relative clauses and wh-questions is 
achieved. 
1 Overview 
1.1 The Grammar 
The ATN-Language used is - except for some 
minor deviations which are not of importance here - 
in accordance with the one specified in \[BATES 78\] 
and covers the following subset of English: 
- the most frequent verb types for declarative 
and imperative sentences and questions 
- direct and indirect WH-questions 
(for NPs, PPs, ADJPs, ADVPs) 
- direct and indirect Y/N-questions 
- sentential complements for verbs 
and nouns 
various types of relative clauses 
(complete, reduced...) 
infintive construction (including control verbs 
with subject and nonsubject control) 
conjunction of complete constituents of every 
syntactic category 
subordinate clauses 
The grammar is written in very compact way, 
making extensively use of merging techniques; it 
comprises about 75 states and 170 arcs. 
The structure built by the grnmmar is cLui.te 
similar to the phrase structure trees usea m 
transformational gr, mmar on the S-structure level. 
(See appendix for some examplesD 
Structures of that type seem to us very suited for 
further semantic interpretation, since they offer a 
level of syntactic structure which both expresses 
~'~mmatical functions (which are defined 
~onfigurationally) and constituent structure 
features which axe important for certain aspects of 
logical form as e.g. quantifier scoping. Especially the 
use of the device of traces (as a phonologically empty 
phrase) allows for displaced elements to appear in 
the phrase marker in their surface postion and at 
the same time expresses the role which this 
element's original position plays in the 
corresponding predicate-argument structure. 
1.2 The Parser 
The parser itself is an active chart parser as 
described in \[KAPLAN 73\] and \[KAY 73\]; a detailed 
desciption of our implementation can be found in 
\[ENDERS et al 82\]. 
By combining an active chart, which represents 
all fully analyzed (sub)constituents (the passive 
edges) and all incomplete partial derivations (the 
active edges) with an agenda, which contains an 
explicit representation of all further tasks to be 
processed, the chart parsing framework is especially 
suited for mul-ti-way analyses on syntacticly and 
lexically highly ambiguous input. 
Furthermore it offers a high degree of flexibility 
in the use of various control-structures beyond the 
uniform ones like depth-first and breadth-first. This 
can be achieved by means of heuristic measures of 
various types which are used for the weighting of the 
single tasks, thus being responsible for the ordering 
of the agenda. Thereby several features of the 
parser such as closure and attachment features and 
preference of certain readings not induced by 
attachment ambiguities can be varied effectively 
by simply modifying this weigthing function. 
There exist three versions of the parser differing 
in the strategy by which the grammar is processed: 
- a top-down version (which is the standard 
case with ATNs) 
- a top-down version augmented with an auto- 
matic one-word look-ahead on PUSH-arcs 
41 
- a mixed bottom-up/top-down version 
The latter two versions which both demand some 
pre-rocessing of the grammar are clearly better in 
terms of performance than the pure top-down 
version. They have about 75% of the memory 
requirements and need 80% of the cpu-time of the 
top-down version. 
All three versions have been implemented in 
Siemens-Interlisp running on Siemens main- 
frames. An implementation on a lisp machine is on 
the way. 
2 Integrating WH-Movement into ATN 
Grammars 
2.1 The Descriptive Adequacy of ATNs 
ATNs, though being a (computationally) 
powerful specification language for grammars are 
not committed to a certain lingistic theory as stated 
cleary in \[WAHLSTER 79\]. This often leads to 
grammars in which various types of syntactic 
phenomena are treated descriptively inadequate 
and linguistically unfounded. In the case of the wh- 
movement phenomena being discussed here, one 
has to cope with the fact that the origin of the 
displaced element can be embedded in some deeper 
clausal constituent arbitrarily far away from its 
surface position. (For an example see figure 2. in the 
appendix !). Sticking to the standard facilities 
offered by ATNs for constructions of that type 
implies the use of SEN'DR actions on PUSH-arcs or 
the HOLD/VIR mechanism in order to allow the 
involved subnets to communicste with each other. I 
But neither of the two possibilities can be viewed 
as a satifactory solution. The former (pushing 
certain register contents through possibly several 
subnets) burdens the gr~rnrnar wrlter with the 
tasks of controlling the use of the pushed register 
either by using it in some network or by pushing it 
further down. It thus puts extreme emphasis on the 
procedural aspect of the grammar thus msk~ng it 
clumsy and hard to comprehend. Therefore this 
approach can hardly be considered as a satisfactory 
solution to the problem. 
The second possibility, namely the use of a 
global register environment and virtual arcs has 
been introduced into the ATN framework in order to 
handle displaced elements of the sort discussed here. 
In this mechanism the HOLD-action offers the 
facility to put an analyzed constituent on the HOLD- 
list (a global additional stack). Later on a VIR-arc 
can consume a constituent from the HOLD-list as if 
it occured at the actual point in the input string. 
The necessity of the use of one of these two 
mechanisms is thereby only under the 
assumption, that the phrase structure to be 
produced is thought to express the functional 
role played by an displaced element in some way or the other. 
Thus the HOLDfVIR facility and extensions of it as 
proposed in \[FININ 83\], though surely being 
preferable to the first possibility still misses to 
express the relevant syntactic restrictions and 
permits violations of grammatical constraints 
governing these constructions. 
Thus to us it seems worthwhile to incorporate 
wh-phenomena into ATN grammars on a 
conceptually higher and syntactically motivated 
level. 
2.2 
2.2.1 
Description of the Approach 
WH-Movement in EST 
Before decribing the embedding of WH- 
movement into an ATN grammar a short 
presentation of the general principles of its 
treatment in EST is given. 
The fundamental feature of it is the use of an 
transformation (move wh-phrase) which moves a 
wh-phrase of a nonverbal phrasal category into an 
sentence°initial non-argument position by adjoining 
it to the COMP-node. The moved phrase leaves 
behind an empty phrase (its trace), which is 
coindexed with the fronted wh-phrase. 
This fronting can be achieved in one step as in 
the unbounded movement analysis or successivly as 
in the COMP-to-COMP analysis, yielding the same 
resulting structure in both cases (ignoring the 
intermediate COMp-deminated traces). The version 
reflected in our approach is the unbounded 
movement analysis as only the COMP-node finally 
dominating the wh-element is affected. 
2.2.2 The ATN-Treatment 
2.2.2.1 General Idea 
The basic idea in the proposed treatment of wh- 
construction is to let the parser build up phrase 
structures containing unbound traces and bind these 
traces to the fronted wh-phrase when the entire wh- 
construction is accomplished. 
This task itself is divided into the following two 
steps: 
. The phrase structure trees built during the 
parse may contain unbound ~aces. At the 
grammar level this is achieved by adding JUMP- 
arcs to the grammar, which can accept empty 
constituents. This means that you have JUMP- 
arcs parsing traces of type XP, which in the 
gr~mm~r are alternative arcs to the 
corresponding PUSH XP-arcs (with XP other 
than VP). Furthermore these arcs contain 
certain register actions responsible for building 
the structures for the empty phrases. 
The possible locations of traces as 
subconstituents in the wh-constrnction phrase 
structure depend on the restrictions described by 
these JUMP-arcs when the grammar is applied 
42 
to the input. 
2. On the level where the phrase structure trees for 
wh-constructions are constructed a binding 
procedure tries to bind (i.e. coindex) the fronted 
wh-phrase with its trace. 
Since this binding procedure is actually the 
central part of the mechanism its features are 
described in more detail in the following section. 
2.2.2.2 The Binding Procedure 
What the binding procedure (BindWhTrace) 
actually does is to establish a mapping of a phrase 
structure tree into another phrase structure tree, 
where the mapping is structure preserving in the 
sense that it does not alter the phrases' internal 
structure. The effect of the mapping is to establish a 
coindexing between a wh-phrase in COMP-position 
and its trace in an argument position as shown in 
the following diagram. 
(S/(COMP(ADJP < +wh>)..)(S..(ADJP e)..)) 
(S/(COMP(ADJP i < + wh > )--)(S-.(ADJPi e)..)) 
The coindexing itself is restricted by various 
constraining conditions. These concern the morpho- 
syntactic,, functional and configurational features of 
the two phrases to be bound. 
So, for example the wh-NP "whom" in COMP- 
position can only be coindexed with an empty NP 
bearingthe grammatical function of direct object or 
prepositional object for example. Furthermore there 
are configurational constraints between the two 
candidate phrases that have to be fullfilled, in order 
to establish a proper binding as e.g. the coordinate 
structure constraint. This constraint does not allow 
movement of a phrase out of a conjunctive structure 
which, being applied to the binding procedure means 
that the coindexing may not take place in a 
structure where f~ is an empty constituent of the 
category XP'. 
(S/(COMP (XP' < + wh > ).)..(XP(XP...I3..) and (XP..).) 
not ----> 
(S/(COMP(XP'i< + wh>).)..(XP(XP..Bi..) and (XP..).) 
Since the phrase structure built at the point 
where the binding procedure is involved may 
contain traces which are no su/table candidates for 
a proper binding (since they do not fullfiU these 
restricting conditions) the procedure may not 
succeed to establish a proper indexing. That's why 
the procedure can also be viewed as a function 
reporting success or failure respectively, thus fil- 
tering out part of the structures btdlt so far. 
Furthermore even in the case of a proper binding 
done by the binding procedure the resulting phrase 
structure trees may still contain unbound traces. 
Such structures however must be blocked according 
to two constraints which do not allow constituents in 
wh-question and relative clause structures to be 
moved outside the entire phrase, which in terms of 
the coindexing means that they may not be 
coindexed with a constituent outside these 
structures. 
In the case of (headed) relative clauses this is 
ruled out by the complex-NP constraint, which 
(stated in a simplified form) does not allow a 
constituent ~ to be moved out of the following 
structure: 
(Np...N/(s/...R...)) 
For questions an equivalent restriction is 
expressed by the wh-island constraint, which does 
not allow a phrase ~ to be moved out of the following 
structure: 
(S/(COMP.. < + wh > )(S.-.fl--.)) 
Since the binding procedure does its work just on 
this sort of phrase structure, namely the structures 
produced by the relative clause and the wh- 
question subnets, it can easily test these two 
constraints too, thus blocking all structures with no 
rOper binding of the displaced wh-element or with 
ftover unbound traces. 
Now the way in which this procedure is 
embedded in the gr~mmex should be clear. It has 
been incorporated into each POP-arc of a wh- 
construction subnet (i.e. the relative clause and the 
wh-question subnet), where it is used as a test- 
predicate reporting whether the structure built so 
far contains a proper binding with no unbound 
traces left. The actual binding is done as a side-effect 
of that predicate. So the corresponding POP-arc look 
Hke this : 
(POP pro' (BindWhTrace pm)) I 
(With pro' derived from the phrase marker pm by 
In terms of the grammar used, a POP-arc for a 
wh-construction network has the following form: 
(0.7 POP (GETR R)(BindWhTrace R)) 
(Here R is the register containing the phrase 
structure tree on which the binding procedure 
works. The first item in this arc is a weight 
assigned to it.) 
43 
successful application of BindWhTrace) 
Thus POP-arcs with an additional test of the sort 
described act as filters popping the form pro' only if 
this test has been sucessfully applied to the 
structure pro. 
2.2.3 Interaction with the Treatment of Control 
Verbs 
As already mentioned our grammar also deals 
with certain contol verb constructions. These axe 
lSO handled by a coindexing procedure which 
nctions similar to the binding procedure. It is 
invoked on the POP-arc of the corresponding 
network and tries - based on the lexical features of 
the control verb in the matrix clause - to coindex the 
abstract subject "Pro" with its controller, also 
reporting success or failure. 
In cases where this coindexing mechanism and 
the binding procedure may affect the same 
constituent (as an example see f~gure 2. of the 
appendix) we have adopted the strategy of doing the 
wh-element binding before the control-indexing. 
This means that the controller-NP may already 
have assigned an index that actually is used for the 
control indexing of Pro. So in our example the final 
structure is constructed in the following way: 
S~COMI~NP < +wh>).)(S-V~V p~rslladeJ(N1~)(S/.(S(Np Pro).)))) 
wh-binding = = ~> 
S~COM~NPI< + wh > ).)(.~(V~V persuade)(Nl~e)(si.(S(Np Pro).)))) 
control binding = -" 
S~COMI~NPI< + wh >).)(S.(VI~V persuade)(l~pie)(s/.(S(Npl Pro).)))) 
The procedure is invoked at the same level, 
namely when a wh-construction is actually parsed 
(i.e. whenever the syntactic rule is applied, which 
combines a wh-element with a phrase of the 
category S.) This roughly corresponds to the POP- 
arc ofa wh-construction subnet in our case. 
But in contrast to our approach where the 
binding procedure acts on a constituent structure 
already containing traces, Wehrli's binding 
procedure is activated by the absence of an 
obligatory slot in the functional structure. After 
locating such a slot an empty element is inserted 
both into the functional and the constituent 
structure with a suitable index. So in his approach 
the search for the argument position traces (which 
in our approach is done by the parser by offering 
different phrase structures already containing 
traces) is part of the binding procedtire. 
This, on the one hand has the advantage of 
focussing on the treatment solely in the binding 
procedure. On the other hand, it makes the ~ 
rocedure considerably more complex, since it must 
e able to detect ambiguities I which in our 
approach are dealt with in the grammar rules. 
2.3.2. PARSIFAL 
The second approach discussed here is the work 
by Marcus on wh-movement in his PARSIFAL 
system \[MARCUS 80\]. There the cyclic analysis of 
wh-movement is adopted which, besides its 
linguistic motivation \[CHOMSKY 77\] is enforced by 
the structure of the gr~mm~r interpreter. The 
reason for this lies in the fact that during the 
parsing of some embedded clause Se there is no 
access to any structure beyond this Se as at that time 
it is the current cyclic node in the active node stack. 
So for example in a structure like 
This reflects the ordering of these two 
mechanisms in transformational gr~rnmRr (namely 
the move-wh transformation and the rules of 
construal) ; thus the correct handling for a wide 
variety of structures involving both wh-movement 
and control constructions has been achieved. 
2.3 
2.3.1 Comparison to other Approaches Wehrli's GB-Parser 
In this section the comparison with other parsers 
is limited to the discussion of the handling of wh- 
constructions only; thus this is not intended an 
overall comparision of the parsers per se. 
One approach to the treatment of wh- 
constructions that lends itself well to a comparison 
can be found in Wehrlis's parser for French 
\[W'EHRL183\]. There a binding procedure is incor- 
porated as a separate module in a parser which in 
toto is based on the GB-framework \[CHOMSK¥ 82\]. 
(S(COMP (NP'< + wh >))...(S, ...(NP ~ e) ...)...) 
at the moment when the trace NP" is parsed (i.e. 
created, dropped into the buffer and attached to Se) 
there is no access to the headed wh-NP NP' thus 
preventing the trace NP" to be bound to it. This 
There may be several unfilled slots in the 
functional structure, in the matrix sentence as 
weU as in some embedded sentence. This is for 
example the case if the headed wh-phrase is a PP 
whose attachment is ambiguous, as in: 
On which day will John hold a speech? 
(.with its "when"-reading "When will .... " and its 
topic'-reading "On which topic will .... ") 
44 
r~blem is avoided, if the gr~mm~r rules create a 
MP-Node with a bound trace attached to it before 
analyzing Se. Thus the trace NP" can be bound to the 
headed wh-NP via some intermediate COMP- 
attached traces, as for example via NP" in the 
following structure: 
(S(COMP (NP' i < + wh > ))--(S,(COMP(NP'i e)..(NP" e).).) 
This mechanism is implemented by means of a 
special register, WH-comp, which in must be 
handled explicitly the grammar rules when creating 
and binding traces. Furthermore the status of that 
register (which can be set in the grammar to 
'utilized" and "not utilized") serves as a condition 
for triggering certain actions in the course of the 
anlysis of wh-constructions (such as the 
deactivation of certain rule packets). This from the 
grsmmar writer's point of view seems to have some 
of the flavour and disadvantages of the SENDR- 
solution discussed before (section 2.1). 
The approach described so far however causes 
difficulties in a productive class of constructions, 
where the trace to be analyzed is dominated by an 
NP which also serves as the current cyclic node 
making the headed wh-phrase inaccessible for the 
binding of its trace as in constructions like: 
(S/(COMP(NP who ))(S is that (NP a portrait of e))) 
Tiffs problem is overcome by Marcus by means of 
an ad hoc mechanism which exactly allows access to 
a headed wh-element in such constructions, whereas 
in our approach constuctions of both types are 
handled in a uniform way. 
3 Conclusion 
The approach described has from our experience 
proved to be a useful step in the direction of 
handling wh-movement constructions in an ATN 
grammar in a linguistically motivated way. The 
resulting gr'~tmrnar turned out to be more 
perspicuous than a grsmmar dealing with these 
phenomena with the standard ATN facilities (as 
sketched in in section 2.1). 
The work described will be continued in three 
directions. First, we will incorporate this 
treatment of wh-constructions and other 
syntactically motivated mechanisms (as for 
example NP-movement) in a grammar for a 
substantial subset of German. Secondly, we will 
include further binding-mechanisms for various 
kinds of anaphoric relationships. Thirdly, we will 
explore the possibility of embedding such concepts 
into the ATN language formalism. 
ACKNOWLEDGEMENTS 
The implementation of the various versions of 
the parser and the grammar editor has been done in 
cooperation with my (partly former) colleagues 
Reinhard Enders, Ludwig Schmid and Bertram 
Fronh6fer. 
REFERENCES 
\[BATES 78\] 
Bates, Madelaine, "Theory and Practice of 
Aug-mented Transition Network Grsmmars", in 
Bolc, Leonard (ed), Natural Language 
Comunication with Computers, Berlin, 1978 
\[BENNIS & GROOS 82\] 
Bennis, Hans, and Groos, Anneke, "Die 
Rektions-Bindungs-Theorie: Neue Aspekte seit 
den 'Aspekten' Zeitschrift f~r Sprachwissenschaft, 
2 (19'82) 
\[CHOMSKY 77\] 
Chomsky, Noam, "On Wh-Movement', in 
Culicover, P. W., Wasow, Thomas, and 
Al~majian, Adrian (eds), Formal Syntax, New 
York, 1977 
\[CHOMSKY 82\] 
Chomsky, Noam, Lectures on Government and Binding, 
Dordrecht 1982 
lENDERS et a182\] 
Enders, Reinhard, Fronh6fer, Bertram, Hau- 
neder, Hans, and Schmid, Ludwig, erlegungen zu einem A TN-C hart-Parser, 
Internal Report (Siemens), 1982 
\[FININ 83\] 
Finin, Timothy W., "An ATN Programming 
Environment , in Bolc, Leonard (ed), The Design of Interpreters, Compilers, and Editors for 
Augmented Transition Networks, Berlin, 1983 
\[GORZ 79\] 
G6rz, Gitnther, "ATN und Kontrollstrukturen", 
in Christaller, Thomas, and Metzing, Dieter 
(eds), Augmented Transition Network Grammatiken, 
Berlin, 1979 
\[KAPLAN 73\] 
Kaplan, Ronald, "A General 
Processor", in Rustin, Randall (ed), Language Processing, 
New York, 1973 
Syntactic Natural 
\[KAY 73\] 
Kay, Martin, '~rhe Mind System", in Rustin, 
Randall (ed), Natural Language Processing, New York, 1973 
\[MARCUS 80\] 
Marcus, Michell P., A Theory of Syntactic Recognition for Natural Language, Cam- 
bridge/MA, 1980 
45 
\[WAHLSTER 79\] 
Wahlster, Wolfgang, ."ATNs und die semantisch-pragmatische Steuerung der 
Analyse undGenerierung natiirlicher Sprache', in Christaller, Thomas, and Metzing, Dieter 
(eds), Augmented Transition Network 
Grammatiken, Berlin, 1979 
\[V~E I.~ 83\] 
Wehrli, Eric, "A Modular Parser For French", in 
Proc. 8th IJCAI Karlsruhe 1983, Los Altos/CA, 
1983 
APPENDIX A. Sample Parses 
8/ 
COMP $ 
PP3 
NP PRP I 
ABOUT QOET I 
WHICH 
N/ 
ADJP N 
OGR AOJ TOPIC I I 
VERY IhlPORTANT 
/+WH NP VP t ~ 
N AUX V PP3 I I I 1 
JOHN /PERF TALK • 
PP 
/,'/~ 
PRP NP I I 
ON N I 
8UNDA'Y' 
F{gure 1. Parse tree for "About which very important topic has John talked on Sunday?" 
8/ 
COMP $ 
NP2 /+~/H NP VP 
NP N PRON AUX V NP2 
/,, I I \[ I I QOET N WOMAN HE /FUT PERSUADE e 
I I WHICH MAN 
8/ 
COMP $ 
/-WH NP2 VP 
Pr'o AUX V NP 
\] I I /-infl DATE PRON 
I Hit4 
Figure 2. Parse tree for "Which man's woman will he persuade to date him?" 
46 
$/ 
COMP S 
/-514 NP ~P 
N ~lJi( V NP NP I I I ~ 
l/ BILL. /PRES GIVE DET N DET I I I 
I 
RELPRON I 
M4ICH 
N I 
BOOK 
$/ 
C0~ $ 
NP2 /-M4 NP ~P' 
PRON At/4( V NP3 $/ 
HE /PRE$ /NEG EXPECT PRON COIqP $ 
HER /-WH NP3 ~P 
Pro AU~I V NP2 I I I 
.~ /-infl RE~ e 
Figure 3. Parse tree for "Bill gives the woman a book which he does not expect her to read." 
47 
