Automaton-based parsing for lexicalized grammars

In wide-coverage lexicalized grammars many of the elementary structures have substructures in common. This means that during parsing some of the computation associated with different structures is duplicated. This paper explores ways in which the grammar can be precompiled into finite state automata so that some of this shared structure results in shared computation at run-time. 1 Introduction This paper investigates grammar precompilation techniques aimed at improving the parsing performance of lexicalized grammars. In a wide-coverage lexicalized grammar, such as the XTAG grammar (XTAG-Group, 1995), many of the elementary structures 1 have substructures in common. If such structures are viewed as independent by a parsing algorithm, the computation associated with their shared structure may be duplicated. This paper explores ways in which the grammar can be precompiled so that some of this shared structure results in shared computation at run-time. We assume as a starting point a co..

Price Cycles and Price Leadership in Gasoline Markets: New Evidence from Canada

This paper studies the determinants of Edgeworth Cycles, price leadership and coordination in retail gasoline markets using daily station-level price data for 110 markets in Ontario, Canada for 2007-2008. We find an “inverse-U” relationship between markets’ propensity to exhibit price cycles and their size. More concentrated markets are less likely to exhibits cycles and we highlight regional clustering among cycling and non-cycling markets. Within cycling markets, we find brands’ stations (Esso, Shell,Petro-Canada, Sunoco) lead price jumps and coordinate market prices, while independents (Ultramar, Pioneer, Olco, MacEwen) aggressively undercut prices over the cycle.Retail gasoline prices; Edgeworth Cycles; Price leadership; Coordination

Encoding Lexicalized Tree Adjoining Grammars with a Nonmonotonic Inheritance Hierarchy

This paper shows how DATR, a widely used formal language for lexical knowledge representation, can be used to define an LTAG lexicon as an inheritance hierarchy with internal lexical rules. A bottom-up featural encoding is used for LTAG trees and this allows lexical rules to be implemented as covariation constraints within feature structures. Such an approach eliminates the considerable redundancy otherwise associated with an LTAG lexicon.Comment: Latex source, needs aclap.sty, 8 page

BNC! Handle with care! Spelling and tagging errors in the BNC

"You loose your no-claims bonus," instead of "You lose your no-claims bonus," is an example of a real-word spelling error. One way to enable a spellchecker to detect such errors is to prime it with information about likely features of the context for "loose" (verb) as compared with "lose". To this end, we extracted all the examples of "loose" used as a verb from the BNC (World edition, text). There were, apparently, 159 occurrences of "loose" (VVB or VVI). However, on inspection, well over half of these were not verbs at all (tagging errors) and over half of the rest were misspellings of "lose". Only about 15% were actual occurrences of "loose" as a verb. This prompted us to undertake a small investigation into errors in the BNC. We report on some words that occur more often as misspellings than in their own right - only one of the 63 occurrences of "ail", for example, is correct (possibly OCR errors) - and some words that are always mistagged, such as "haulier" and "glazier" (never NN), and "hanker" and "loiter" (never VV). We note in particular that, if a rare word resembles a common word (in spelling), it is more likely to appear as a misspelling of the common word than as a correct spelling of the rare word. These cases require some modification of an earlier conclusion (Damerau and Mays, 1989) on misspellings of rare words. We conclude with a discussion of the desirability, or otherwise, of correcting errors in corpora such as the BNC. The results may be of interest to people who use the BNC as training data or for teaching

Integrable Lattice Models for Conjugate An(1)A^{(1)}_n

A new class of $A^{(1)}_n$ integrable lattice models is presented. These are interaction-round-a-face models based on fundamental nimrep graphs associated with the $A^{(1)}_n$ conjugate modular invariants, there being a model for each value of the rank and level. The Boltzmann weights are parameterized by elliptic theta functions and satisfy the Yang-Baxter equation for any fixed value of the elliptic nome q. At q=0, the models provide representations of the Hecke algebra and are expected to lead in the continuum limit to coset conformal field theories related to the $A^{(1)}_n$ conjugate modular invariants.Comment: 18 pages. v2: minor changes, such as page 11 footnot