REVISING AN ATN PARSER 
Giacomo Ferrari, Irina Prodanof 
Istituto dl Linguistica Computazionale, CNR, Pisa, Italy 
1. An ATN parser for Italian has been developed and 
tested in a series of experiments on complex sentences taken 
from narrative texts (1,2,3,4). The construction of a complex 
graemmz as well as the results of our experiments showed some 
limits and inadequacies of Woods" ATN as it stands (11), 
especially when used to parse Italian, a relatively free- 
order language with a well developed morphological system. 
1.1. "Parameter-passing" actions such as SENDR and 
LIFTR have been often Judged "dirty" operations under a form- 
al view-point. Moreover it is almost impossible to keep the 
control of the cross-level pa~sed information, unless the 
~umber of registers is increased. Such an increase is other- 
wise unmotivated. This difficulty is more evident in Italian 
relative clauses such as: 
L" uomo la cui crudelta" tutti conoseiamo 
The man (the) whose cruelty everyone knows 
L" uomo la crudelta" del quale tutti conoscismo 
The man the cruelty of whom everyone knows 
L ° uomo del desiderio di vendetta del quale ti he parlato 
The man about the desire for revenge of whom I spoke to you 
in which a very heavy use of such actions, as well as of 
flags, is required. These phenomena, together with the rich- 
ness of morphological inflexion, increase the necessity for 
morphological and morpho-syntactic short, long-distance and 
cross-level tests. 
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1.2, Another problem is proposed by the structural ambi- 
8~ity of sequences of PP's, for which both the "embedding" and 
the "same-level" hypotheses are presented! a sentence with ) 
PP's has 5 parses accordlng to the schema 
(PPI (PP2 (PP3))), (PPI (PF2)(PP3)), (PFI (PI~) PP3),(PP1 
P~ (PP3)), (PP1 P~ PP3) 
An attempt to limit th~s explosion was made by adding oertaln. 
functional labels depending upon the verb frame. This experim- 
ent showed that attention should be focussed on developing an 
adequate system of functional tests. 
1.3. A statistically based, dynsmic heuristic mechanism 
has been put to work in the traversal of the network. Those 
paths which have been more frequently traversed in previous 
parsed frasments of a given text are attempted first, during 
the analysis of the CUZTent sentence (6). 
In this way, the concept of performance based syntactic 
expectation has been introduced and tested. It appeared that 
ATN is very suited to the introduction of heuristic techniques 
and also that these techniques should include a scheduling 
procedure based on arc types (10). 
2. A revision of the linguistic formalism as well as of 
the parsing alSorithm is now in progress, and should take all 
these considerations into account. Furthermore, those linsuist- 
io phenomena related to conversation such as anaphora and the 
analysis of partial and partially correct input must be taken 
into account in the desis~ing of the formalism and the ATN 
actions and forms, not only for applicative purposes, but 
above all in order to enlarge the range of phenomena to be 
included in a ~ammar. 
2.1. The parser relies both on structural and functional 
Information (7), i,e. a limited collection of surface struct- 
ures and functional labels. A set of fixed (control) pattsz~s 
might also be included in this static syntactic knowledge 
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(B, 9)• The output representation, however, is in terms of 
functional labels• The utilization of these three data types 
will be fully discussed. 
2.2. It is not our intention to substantially modify 
the general structure of the algorithm• Storing and retriev- 
ing will be modified, in accordance with our observations in 
1.1. A single register external to the levels of computation 
will be progressively set to the results of the analysis 
during parsing. Access to precise location of this structure 
is guaranteed by the functional labels. Traditional ATN 
registers can be locally used for special purposes. A detail- 
ed description of our whole mechanism including examples will 
be given• 
Already assigned functional labels cannot be chanEed! 
left concatenation of them has been preferred (8). A mechanism 
has also been provided to move pointers from constituents to 
gape or anaphorical pronouns (inside the sentence borders) (5). 
This is an attempt to treat by a uniform action or sequence 
of actions equ/-NP deletion, gapplng, coordination. 
2.3. Some local procedures connected with the lexicon 
have been added to these mechanisms. These procedures include 
the transmission of feature's to higher level nodes in the 
structure, the proceduralisation of idiosyncrasies of single 
leKical entries and "paraphrase'. The latter is expected to 
reduce nominalizatlon to the corresponding verb with its 
frame components and to account for linguistic units which 
have identical distribution and syntactic behavlour. 
2.4• The present list of "linguistically* motivated 
processes is open-ended, as we are now trying to identify 
others, which can be considered to be linguistic (procedural) 
°um/versals "• 

References

(1) A.Oappelll, G. Perrari, L. Moretti, I. Prodanof, O. Stocks 
~Parsing an Italian text with an ATN parser', report ILC, 
Flee@ 1978. 

(2) A.Oappelli, G. Ferrari, L. Morettl, I. Prodanof, O, Stocks 
"An ATN parser for Italian: an experiment', Atti del 
COLING 78, Stocoolma (microflches). 

(3) A.Cappelll, G. Ferrari, L. Morettl, I. Prodanof, O.Stook: 
"Analisi di un testo Italiano con un analizzatore ATN °, 
Riviera dl Informatioa, X 3 (1980), pp. 5-13. 

(4) A.Cappelll, G.Ferrari, L. Morettl, I. Prodanof, O. Stock: 
"Analisi automatica dell" italiano: alcu.ne oeservazioni*, 
in La ricerca di base in peicologia. Attl del XVIII Con- 
gresso de@ll Psicologl Italianl, Aoireale 29/X - 2/XI 
1979, 1980, pp. 246-267. 

(5) A. Cappelli,G.Perra~i, L. Morsttl, I.lh~odanof, 0.Stookl 
"Ii trattamento di alcuni fenomenl anaforici mediante un 
ATN', Atti del semlnario "L'anafora'tenuto preeso l'Acca- 
demia della Orueoa, Pirenze 14-16/12/78. In corso di 
S~ampa, 

(6) G.Parrarl, O. Stock: "Strategie selection for an ATN Syn- 
tactic Parser', in The 18th Annual Meeting of the Assoo- 
lation for Computational Linguistics and parasesslon on 
Topics in Interactive Discourse. Proceedings of the Con- 
ference, June 19-22, 1980, Philadelphia, pp. 113-115. 

(7) R. Kaplan, J. Breenan: Lexieal-Functlonal Grsmmar: A 
formal system for grammatical representation, to appear 
in J.Bresnan (ed.), The mental representation of grammat- 
ical relations, MIT Press. 

(8) M. Kay: "Functional Grammar*, in Proc. of the 5th meeting 
of the Berkeley Linguistic Society, Berkeley 1979, pp. 
142-I 58. 

(9) S.Kwasny, N. Sondhelmer: "Relaxation techniques for pars- 
ing ill-formed input', in AJCL 7, 2 (april-June 1981), 
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pp. 99-108. 

(10) E. Weaner, ~. Maratsos: "An ATN approach to comprehension" 
in ~° Halle, J. Bresnan, G. Miller (eds.) Linguistic 
Theory and PsyChological Reality, NIT Press 1978. 

(11) W° Woods: "Transition Network Grammars for Natural lanS- 
uase Analysis', in CAOM 13~I0, New York, 1970, 
