Difference between revisions of "Norwegian HPSG grammar NorSource"

Revision as of 20:24, 26 April 2014

See the web demo of the Norwegian HPSG grammar Norsource.

License

[WWW] Lesser General Public License For Linguistic Resources

The grammar

NorSource is a computational grammar of Norwegian, developed through the last 12 years. It has as its formal and theoretical framework Head-Driven Phrase Structure Grammar (HPSG) (Pollard and Sag 1994, Sag et al. 2003), and started as a computational project through the LinGO initiative at CSLI, Stanford, using the LKB platform (Copestake 2002), which is a general platform with the format of typed feature-structures (TFS), and has integrated in it a format of semantic representation called Minimal Recursion Semantics (‘MRS’; cf. Copestake et al. 2005). Before year 2000 there were three grammars in this framework, viz. the English Resource Grammar ('ERG'), the Japanese grammar 'Jacy', and the German grammar 'GG'. Essential to the development of further grammars of this type was the HPSG Grammar Matrix (‘the Matrix’; see Bender et al. 2002, 2010), which was mainly based on ERG, and had its first phase of deployment during the EU-project DeepThought (2002-4). The grammars of this type are currently developed within the frame of the DELPH-IN consortium, and will in the following be referred to as the ‘DELPH-IN grammars’.

Norsource was started by linguists versed in Generative Grammar since the late 60ies, and formal semantics (like ‘Montague Grammar’) since the mid 70ies. From the mid 80ies the group developed a computational lexicon TROLL, see Hellan et al. 1989). The group mainly associated with research within ‘consolidated GB’, but in the late 90ies it reoriented towards HPSG, and started Norsource as part of DeepThought. Despite never receiving very substantial funding, the grammar has a place among the medium-large DELPH-IN grammars. We can distinguish four main phases in its development:

 Phase 1, the Grounding phase (2001-04), 
 Phase 2, the Semantic Expansion phase (2005-07), 
 Phase 3, the Cross-Linguistic Coding phase (2008-10), 
 Phase 4, the Deployment and Interoperability phase (2010-14).

Phase 1 resided in the building of a basic core grammar around the Matrix skeleton (using the Matrix versions 0.1 – 0.6, as they developed; this included the MRS system). This stage included the accommodation of a 80,000 entries lexicon imported from the previously established resources TROLL and NorKompLex, where a verb valence code and a code for inflectional paradigms constituted major parts.

Phase 2 resided in the development of a fine-grained ontology and computing system of spatial and temporal relations, amenable to grammatical systems across languages and typologies, and a detailed semantics of comparative constructions. The grammar was also used as a part of a small Norwegian-Japanese MT system. In this period, the inflectional system was thoroughly revised. Main publications from this period are: Hellan and Beermann (2004), Bermann et al. (2004), Beermann and Hellan (2005).

Phase 3 was devoted to a thorough revision of the valence code, to accommodate a cross-linguistically defined classification system of valence and construction types. Main publications from this period are: Hellan (2008), Hellan and Dakubu (2009, 2010)

Phase 4 can be divided into the following themes:

A. Deploying the grammar in ‘external’ applications: a ‘Grammar Sparrer’, as described in Hellan et al. 2013, accessed at A Norwegian Grammar Sparrer. This is a construct along the lines of Bender et al. 2004, and Suppes et al. 2014, falling within the overall initiatives described in Heift and Schultze 2007, where specific types of grammatical mistakes are accommodated by ‘mal-rules’ in an extended ‘mal’-version of the grammar, and parses involving such mal-phenomena are reported to the user as tutoring instructions. This system has been running as a webdemo since 2011.

B. Exporting information from the grammar to independent resources:

 1. A valence bank, which, with the same exporting strategy as for Norwegian, contains also two other 
 languages, constituting the first instance of an in depth Multilingual Valence repository. In essence,   
 the valence code used in verbal lexical types (cf. 3.2 below) is expanded to alternative and more easily  
 inspectable formats, and the verb lexicons of the languages involved are imported into a database
 organized according to the newer codes, and searchable in terms of these codes. (See Hellan and Bruland
 2013, and a web access at Multilingual Verb Valence Lexicon.)

 2. A POS-tagger reflecting the lexical inventory of the grammar, useful for lexical acquisition from new  
 text ( (http://regdili.idi.ntnu.no:8080/webtagger/tagger )).

 3. A simple Reasoner over movement and spatial information exported from the MRS. (See Bruland 2013.)

C. Updating the soft- and hardware basis of the grammar (in particular with ACE), and the construction of a server carrying web-facilities for the grammar itself, as well as the applications and resources just mentioned.

D. General regimentation of the grammar code.

E. Adapting the semantic system – MRS – according to the UTool restrictor on MRS objects, enabling the Reasoner mentioned above. (See Bruland 2013)

F. Aligned with the latter point, exploring ways of simplifying the grammar definition code, which in its Matrix shape is a remnant from a far more complex AVM notation system (from Pollard and Sag 1994) than is currently motivated. (See Hellan, forthcoming)

Point F is developed along a scheme of building small grammars for the exploration of specific features or alternative designs. A full computational grammar as such is a very ‘stiff’ construct where hardly any change can be made without many repercussions elsewhere in the structure, hence no major change is advisable unless it has been explored in a smaller format.

Purposes of the grammar

As a grammar of Norwegian, Norsource's first and foremost purpose is of course coverage in the sense in which a descriptively adequate Generative Grammar is supposed to attain coverage, namely through recursive enumeration of all and only the strings that count as grammatical in the language, and assigning each string so recognized a morpho-syntactic and semantic analysis. Correctness of analysis is decided on empirical grounds, using standard linguistic criteria of adequacy.

Creating such a grammar as a computational system requires formal consistency down to the smallest details, far beyond what could be done in a theoretical grammar. Given the size of a system aspiring to meeting the above goals, a set of formal constraints that can be sustained throughout the life cycle of the grammar, constitutes a significant insight into the principles by which a language is built up. Although no such set of constraints is unique - a language can presumably have grammars assigned in more than one way - as a 'successful' set of constraints carrying a grammar, any such set constitutes an important contribution to the general theory of language. Thus, a computational grammar is a strong contribution to general linguistic theory.

As a computational system, a further desideratum is that the grammar can serve as a component in one or more natural language processing applications.

From the viewpoint of general linguistics, the latter concern has the proviso that for a grammar as a ‘generic’ device, its success in the usage domain should in principle be measured by how well it can go into a multitude of applications, not just a single one; this is also the ambition for the present grammar. In this respect the grammar is like a Fregean ‘Sinn’, in acting as a function from domains-of-use to deployable systems.

Moreover, the grammar has been developed with a view to the following overall desiderata:

Cross-grammar Generality

The content of the grammar should to as large an extent as possible be phrased in terms used or alignable with terms used in other grammars and for other languages, thereby enabling linguistic comparison using these grammars.

Interoperability

The grammar should attain as much interoperability with other applications as possible, manifested both on an ‘outer’ level enabling data flow and easy access, and on an ‘inner’ level ensuring information exchange from one system component to another. Thus, the grammar's files and productions (parses, etc.) should be transportable to other applications, and the codes in which its files are written should be readable by other applications, or able to be mapped into other codes.

Sustainability

The grammar should be in such a format, and be situated in such an over-all environment, that as much as possible of its capacity can be retained, independently of particular persons maintaining it or particular physical environments.

Adequacy of the grammar

The grammar must cover not only ‘core grammar’, but the whole array of constructs that can be used in texts of the language: ‘fragments’, abbreviations, interjections, and much more. It at the same time must attain ‘analytic depth’, which will include at least the following factors of morpho-syntactic structure and parameters of functional and semantic analysis (in addition comes a lexicon of significant size):

 - syntactic argument structure (or valence:  whether there is a subject, an object, 
 a  second/indirect object, etc., referred to as grammatical functions); 
 - semantic argument structure, that is, how many participants are present in the situation depicted,
 and possibly also which roles they play (such as ‘agent’, ‘patient’, etc.);
 - linkage between syntactic and semantic argument structure, i.e., which grammatical functions 
 express which roles; - identity relations, part-whole relations, etc., between arguments;
 - aspect and Aktionsart, that is, properties of the situation expressed by a sentence in terms of 
 whether it is dynamic/stative, continuous/instantaneous, completed/ongoing, etc..

If these, and other, factors can be addressed in a notional and formal system so cross-linguistically articulated that a grammar of a language L1, through its formal encoding, exposes values relative to the above parameters within a matrix of corresponding values for languages L2, L3, …, etc., then one is on the track of attaining the desideratum of cross-grammar generality. To a certain extent, the multilingual valence base mentioned above under phase 4, point A, is an illustration of this point.

A standard requirement on NLP applications is that they be amenable to evaluation. However, there exist so far few criteria for measuring how well a grammar as a whole performs with regard to 'analytic depth' or the other desiderata mentioned. The closest a grammar can come currently to being transparent for its adequacy is through certains types of 'self-declaration', of which we mention two:

 - Test suites categorized for what analytic properties their parses should exhibit;
 - Grammar internal categorization systems which carry agreed-upon general definitions, 
 the grammar thereby signaling that the constructs categorized have been designed 
 with the agreed-upon contents.

Both strategies are followed in the present grammar. The Test suites shown below reflect the performance of the grammar for the phenomena contained in the various suites, and in the grammar internal classification, the verb type encoding is defined following the system laid out in

References

Beermann, D and L. Hellan. 2004. A treatment of directionals in two implemented HPSG grammars. In Stefan Müller (ed) Proceedings of the HPSG04 Conference, Katholieke Universiteit Leuven. CSLI Publications /http://csli-publications.stanford.edu/

Bender, E. M., D. Flickinger, and S. Oepen. 2002. The Grammar Matrix: An open-source starter kit for the rapid development of cross-linguistically consistent broad-coverage precision grammars. In Proceedings of the Workshop on Grammar Engineering and Evaluation, Coling 2002, Taipei.

Bender, E. M., D. Flickinger, S. Oepen and A. Walsh (2004). "Arboretum: Using a precision grammar for grammar checking in CALL," in Proceedings of the InSTIL/ICALL Symposium 2004, Venice, Italy.

Bender, E. M., Drellishak, S., Fokkens, A., Poulson, L. and Saleem, S. 2010. Grammar Customization. In Research on Language & Computation, Volume 8, Number 1, 23-72.

Bruland, T. 2013. Building World Event Representations From Linguistic Representations. PhD dissertation, NTNU.

Copestake, A. 2002. Implementing Typed Feature Structure Grammars. CSLI Publications, Stanford.

Copestake, A., D. Flickinger, I. Sag and C. Pollard. 2005. Minimal Recursion Semantics: an Introduction. Journal of Research on Language and Computation. 281-332.

Heift, T., and M. Schulze. (2007). Errors and Intelligence in Computer-Assisted Language Learning: Parsers and Pedagogues. Routledge, New York.

Hellan, L. 1988. Anaphora in Norwegian and the Theory of Grammar. Kluwer.

Hellan, L. and D. Beermann. 2005. Classification of Prepositional Senses for Deep Grammar Applications. In: Kordoni, V. and A. Villavicencio (eds.).

Hellan, L.., L. Johnsen and A. Pitz. 1989. TROLL. Ms., NTNU

Hellan, L. (2008). Enumerating Verb Constructions Cross-linguistically. In Proceedings from COLING Workshop on Grammar Engineering Across frameworks. Manchester. http://www.aclweb.org/anthology-new/W/W08/#1700 .

Hellan, L. and M.E.K. Dakubu (2009): A methodology for enhancing argument structure specification. In Proceedings from the 4th Language Technology Conference (LTC 2009), Poznan.

Hellan, L. and M. E. K. Dakubu, 2010: Identifying Verb Constructions Cross-Linguistically. Studies in the Languages of the Volta Basin 6.3. Legon: Linguistics Dept., University of Ghana

Hellan, L. and T. Bruland 2013. Constructing a Multilingual Database of Verb Valence. NoDaLiDa, Oslo, 2013.

Hellan, L. T. Bruland, M. Sandøy, E. Aamot. 2013. A Grammar Sparrer for Norwegian. NoDaLiDa, Oslo, 2013.

Pollard, C. and Sag, I. (1994). Head-Driven Phrase Structure Grammar. Chicago University Press.

Suppes, P, T. Liang, E.E. Macken and D. Flickinger (2014) “Positive technological and negative pre-test-score effects in a four-year assessment of low socioeconomic status K-8 student learning in computer-based Math and Language Arts courses ", Computers & Education, 71, pp. 23-32.

Test suites

Complete test suites for basic verbal constructions are found in

• Verbconstructions Norwegian - intransitive,
• Verbconstructions Norwegian - transitive,
• Verbconstructions Norwegian - ditransitive and copular.