Over the past few years significant progress was accomplished in efficient processing with wide-coverage hpsg grammars. hpsg-based parsing systems are now available that can process medium-complexity sentences (of ten to twenty words, say) in average parse times equivalent to real (i.e. human reading) time. A large number of engineering improvements in current hpsg systems were achieved through collaboration of multiple research centers and mutual exchange of experience, encoding techniques, algorithms, and even pieces of software. This article presents an approach to grammar and system engineering, termed competence & performance profiling, that makes systematic experimentation and the precise empirical study of system properties a focal point in development. Adapting the profiling metaphor familiar from software engineering to constraint-based grammars and parsers, enables developers to maintain an accurate record of system evolution, identify grammar and system deficiencies quickl...

In this paper, we first introduce a new architecture for parsing, bidirectional incremental parsing. We propose a novel algorithm for incremental construction, which can be applied to many structure learning problems in NLP. We apply this algorithm to LTAG dependency parsing, and achieve significant improvement on accuracy over the previous best result on the same data set. 1

Parsing schemata provide a high-level formal description of parsers. These can be used, among others, as an intermediate level of abstraction for deriving the formal correctness of a parser. A parser is correct if it duely implements a parsing schema that is known to be correct. In this paper it is discussed how the correctness of a parsing schema can be proven and how parsing schemata relate to some well-known classes of parsers, viz. chart parsers and LR-type parsers.

We compare the effectiveness of two related machine translation models applied to the same limited-domain task. One is a transfer model with monolingual head automata for analysis and generation; the other is a direct transduction model based on bilingual head transducers. We conclude that the head transducer model is more effective according to measures of accuracy, computational requirements, model size, and development effort.

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We discuss a generalization of Earley's algorithm to grammars licensing discontinuous constituents of the kind proposed by the so-called linearization approaches in Head-Driven Phrase Structure Grammar. We show that one can replace the standard indexing on the string position by bitmasks that act as constraints over possible coverage bitvectors. This improves efficiency of edge access and reduces the number of edges by constraining prediction to those grammar rules which are compatible with known linearization properties. The resulting parsing algorithm does not have to process the right-hand side categories in the order in which they cover the string, and so one can obtain a head-driven strategy simply by reordering the right-hand side categories of the rules. The resulting strategy generalizes head-driven parsing in that it also permits the ordering of non-head categories.

It has been suggested that, in certain circumstances, it might be useful for a grammar-writer to annotate which rules are to be used bottom-up and which are to be used top-down within a parser, using a bidirectional variant of the active chart parsing technique. The formal properties of such systems have not been fully explored. One limitation of this mixed strategy technique is that certain annotations of rules can lead to incompleteness; that is, there may be valid analyses of the input string which cannot be found by the parser. We formalise a fairly natural notion of mixed strategy bidirectional parsing for context free grammars, in which one or more symbols within a rule may be annotated as “triggers ” so that the rule is either top-down (triggered from its left-hand side), or bottom-up (triggered from element(s) of its right-hand side). We define a decidable property of annotated grammars, such that any grammar with this property is provably complete. There are, however, some complete annotations of grammars which fall outside this decidable class. We show that membership of this wider class is undecidable. These results suggest that the mixed strategy approach is of rather limited usefulness, regardless of whether it is empirically efficient or not.

We investigated the performance efficacy of beam search parsing and deep parsing techniques in probabilistic HPSG parsing using the Penn treebank. We first tested the beam thresholding and iterative parsing developed for PCFG parsing with an HPSG. Next, we tested three techniques originally developed for deep parsing: quick check, large constituent inhibition, and hybrid parsing with a CFG chunk parser. The contributions of the large constituent inhibition and global thresholding were not significant, while the quick check and chunk parser greatly contributed to total parsing performance. The precision, recall and average parsing time for the Penn treebank (Section 23) were 87.85%, 86.85%, and 360 ms, respectively. 1

Many modern grammatical formalisms divide the task of linguistic specification into a context-free component of phrasal constraints and a separate component of attribute-value or functional constraints. Conventional methods for recognizing the strings of a language also divide into two parts so that they can exploit the different computational properties of these components. This • paper focuses on the interface between these components as a source of computational complexity distinct from the complexity internal to each. We first analyze the common hybrid strategy in which a polynomial context-free parser is modified to interleave functional constraint solving with context-free constituent analysis. This strategy depends on the property of monotonicity in order to prune unnecessary computation. We describe a number of other properties that can be exploited for computational advantage, and we analyze some alternative interface strategies based on them. We present the results of preliminary experiments that generally support our intuitive analyses. A surprising outcome is that under certain circumstances an algorithm that does no pruning in the interface may perform significantly better than one that does. 1.

We describe and argue for a strategy of performance profiling and comparison in the engineering of parsing systems for wide-coverage linguistic grammars. A performance profile is a precise, rich, and structured snapshot of system (and grammar) behaviour at a given development point. The aim is to characterize system performance at a very detailed technical level, but at the same time to abstract away from idiosyncracies of particular processors. Profiles are obtained with minimal effort by applying a specialized profiling tool to a set of structured reference data (taken from both existing test suites and corpora), in conjunction with a uniform format for test data and processing results. The resulting profiles can be analyzed and visualized at various levels of granularity in order to highlight different aspects of system performance, thus providing a solid empirical basis for system refinement and optimization. Since profiles are stored in a database, comparison with earlier versions, differe...