Phrasal Analysis of Long Noun Sequences

Phrasal Analysis of Long Noun Sequences Yigal Arens, John J. Granacki, and Alice C. Parker University of Southern California Los Angeles, CA 90089-0782 ABSTRACT Noun phrases consisting of a sequence of nouns (sometimes referred to as nominal compounds) pose considerable difficulty for language analyzers but are common in many technical domains. The problems are compounded when some of the nouns in the sequence are ambiguously also verbs. The phrasal approach to language analysis, as imple- mented in PHRAN (PHRasal ANalyzer), has been extended to handle the recognition and partial analysis of such constructions. The phrasal analysis of a noun sequence is performed to an extent sufficient for continued analysis of the sen- tence in which it appears. PHRAN is currently being used as part of the SPAN (SPecification ANalysis) natural language interface to the USC Advanced Design AutoMation system (ADAM) (Granacki ct at, 1985). PHRA_N-SPAN is an inter- face for entering and interpreting digital system specifications, in which long noun sequences occur often. The extensions to PHRAN's knowledge base to recognize these constructs are described, along with the algorithm used to detect and resolve ambiguities which arise in the noun sequences. 1. Introduction In everyday language we routinely encounter noun phrases consisting of an article and a head noun, possibly modified by one or more adjectives. Noun-noun pairs, e.g., park bench, atom bomb, and computer programmer, are also common. It is rare, however, to encounter noun phrases consisting of three or more nouns in sequence. Consequently, research in natural language analysis has not con- centrated on parsing such constructions. The situation in many technical fields is quite different. For example, when describing the specifications of electronic systems, designers com- monly use expressions such as: bus request cycle transfer block size segment trap request interrupt vector transfer phase arithmetic register transfer instruction. During design specification such phrases are often constructed by the specifier in order to refer- ence a particular entity: a piece of hardware, an activity, or a range of time. In most cases, the nouns preceding the last one are used as modifiem, and idiomatic expressions are very rare. In almost all cases the meaning of noun sequences can there- fore be inferred largely based on the last noun in the sequence*. (But see Finin (1980) for in-depth treatment of the meaning of such constructions). The process of recognizing the presence of these expressions is, however, complicated by the fact that many of the words used are syntactically ambiguous. Almost every single word used in the examples above belongs to both the syntactic categories of noun and verb. As a result, bus request cycle may conceivably be understood either as a corn- * When a sequence has length three or more the order of modification may vary. Consider: lengine damage] report January [aircraft repairs I [boron epoxyl [ [rocket motor] chambers l 1970 I [balloon flight I [ [solar-cell standardization l program] ]. But the last noun is still the modified one. These examples are from (Rhyne, 1976) and …

Content truncated to 500 words