Browsing by Subject "two-level morphology"

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  • Koskenniemi, Kimmo (The Association for Computational Linguistics, 1984)
    A language independent model for recognition and production of word forms is presented. This "two-level model" is based on a new way of describing morphological alternations. All rules describing the morphophonological variations are parallel and relatively independent of each other. Individual rules are implemented as finite state automata, as in an earlier model due to Martin Kay and Ron Kaplan. The two-level model has been implemented as an operational computer programs in several places. A number of operational two-level descriptions have been written or are in progress (Finnish, English, Japanese, Rumanian, French, Swedish, Old Church Slavonic, Greek, Lappish, Arabic, Icelandic). The model is bidirectional and it is capable of both analyzing and synthesizing word-forms.
  • Koskenniemi, Kimmo (2013)
    The paper shows how a certain kind of underlying representations (or deep forms) of words can be constructed in a straightforward manner through aligning the surface forms of the morphs of the word forms. The inventory of morphophonemes follows directly from this alignment. Furthermore, the two-level rules which govern the different realisations of such morphophonemes follow fairly directly from the previous steps. The alignment and rules are based upon an approximate general metric among phonemes, e.g., articulatory features, that determines which alternations are likely or possible. This enables us to summarise contexts for the different realisations.
  • Yli-Jyrä, Anssi Mikael (The Association for Computational Linguistics, 2011)
    This paper describes a non-conventional method for compiling (phonological or morpho-syntactic) context restriction (CR) constraints into non-deterministic automata in finite-state tools and surface parsing systems. The method reduces any CR into a simple one that constraints the occurrences of the empty string and represents right contexts with co-determististic states. In cases where a fully deterministic representation would be exponentially larger, this kind of inward de- terminism in contexts can bring benefits over various De Morgan approaches where full determinization is necessary. In the method, an accepted word gets a unique path that is a projection of a ladder-shaped structure in the context recognizer. This projection is computed in time that is polynomial to the number of context states. However, it may be difficult to take advantage of the method in a finite-state library that coerces intermediate results into canonical automata and whose intersection operation assumes deterministic automata.
  • Yli-Jyrä, Anssi Mikael (Northern European Association for Language Technology, 2011)
    NEALT Proceedings Series
    A novel technique of adding positionwise flags to one-level finite state lexicons is presented. The proposed flags are kinds of morphophonemic markers and they constitute a flexible method for describing morphophonological processes with a formalism that is tightly coupled with lexical entries and rule-like regular expressions. The formalism is inspired by the techniques used in two-level rule compilation and it practically compiles all the rules in parallel, but in an efficient way. The technique handles morphophonological processes without a separate morphophonemic representation. The occurrences of the allomorphophonemes in latent phonological strings are tracked through a dynamic data structure into which the most prominent (i.e. the best ranked) flags are collected. The application of the technique is suspected to give advantages when describing the morphology of Bantu languages and dialects.
  • Koskenniemi, Kimmo (Northern European Association for Language Technology, 2013)
    NEALT Proceedings Series
    Regular correspondences between historically related languages can be modelled using finite-state transducers (FST). A new method is presented by demonstrating it with a bidirectional experiment between Finnish and Estonian. An artificial representation (resembling a proto-language) is established between two related languages. This representation, AFE (Aligned Finnish-Estonian) is based on the letter by letter alignment of the two languages and uses mechanically constructed morphophonemes which represent the corresponding characters. By describing the constraints of this AFE using two-level rules, one may construct useful mappings between the languages. In this way, the badly ambiguous FSTs from Finnish and Estonian to AFE can be composed into a practically unambiguous transducer from Finnish to Estonian. The inverse mapping from Estonian to Finnish is mildly ambiguous. Steps according to the proposed method could be repeated as such with dialectal or older written texts. Choosing a set of model words, aligning them, recording the mechanical correspondences and designing rules for the constraints could be done with a limited effort. For the purposes of indexing and searching, the mild ambiguity may be tolerable as such. The ambiguity can be further reduced by composing the resulting FST with a speller or morphological analyser of the standard language.
  • Koskenniemi, Kimmo Matti; Kuutti, Pirkko (Research Institute for Linguistics, Hungarian Academy of Sciences, 2017)
  • Koskenniemi, Kimmo (CSLI publications, 2019)
    CSLI Lecture Notes