Parsing a Free-Word Order Language: Warlpiri

PARSING A FREE-WORD ORDER LANGUAGE: WARLPIRI Michael B. Kashket Artificial Intelligence Laboratory Massachusetts Institute of Technology 545 Technology Square, room 823 Cambridge, MA 02139 ABSTRACT Free-word order languages have long posed significant problems for standard parsing algorithms. This paper re- ports on an implemented parser, based on Government- Binding theory (GB) (Chomsky, 1981, 1982), for a par- ticular free-word order language, Warlpiri, an aboriginal language of central Australia. The parser is explicitly de- signed to transparently mirror the principles of GB. The operation of this parsing system is quite different in character from that of a rule-based parsing system, ~ e.g., a context-free parsing method. In this system, phrases are constructed via principles of selection, case-marking, case- assignment, and argument-linking, rather than by phrasal rules. The output of the parser for a sample Warlpiri sentence of four words in length is given. The parser was executed on each of the 23 other permutations of the sentence, and it output equivalent parses, thereby demonstrating its ability to correctly handle the highly scrambled sentences found in Warlpiri. INTRODUCTION Basing a parser on Government-Binding theory has led to a design that is quite different from traditional algo- rithms. 1 The parser presented here operates in two stages, lexical and syntactic. Each stage is carried out by the same parsing engine. The lexical parser projects each con- stituent lexical item (morpheme) according to information in its associated lexical entries. Lexical parsing is highly data-driven from entries in the lexicon, in keeping with GB. Lexical parses returned by the first stage are then handed over to the second stage, the syntactic parser, as input, where they are further projected and combined to form the final phrase marker. Before plunging into the parser itself, a sample Warl- piri sentence is presented. Following this, the theory of ar- gument (i.e., NP) identification is given, in order to show how its substantive linguistic principles may be used di- rectly in parsing. Both the lexicon and the other basic data structures are then discussed, followed by a descrip- tion of the central algorithm, the parsing engine. Lexical phrase-markers produced by the parser for the words kur- 1 Johnson (1985} reports another design for analyzing discontinuous constituents; it is not grounded on any linguistic theory, however. duku and puntarni are then given. Finally, the syntactic phrase-marker for the sample sentence is presented. All the phrase-markers shown are slightly edited outputs of the implemented program. A SAMPLE SENTENCE In order to make the presentation of the parser a little less abstract, a sample sentence of Warlpiri is shown in (1): (1) Ngajulu-rlu ka-rna-rla punta-rni kurdu-ku karli. I-ERG PRES-1-3 take-NPST child-DAT boomerang 'I am taking the boomerang from the child.' (The hyphens are introduced for the nonspeaker of Warlpiri in order to clearly delimit the morphemes.) The second word, karnarla, is the auxiliary which must appear in the second (Wackernagel's) position. Except for the auxiliary, the other words may be uttered in any order; there are 4! ways of saying this sentence. …

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