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• Lexical class-dependent screeve formation (e.g. the endings in the
Aorist);
• The dependency between the formation of some screeves from that of
others (e.g. the Imperfect from the Present); and
• The multiple exponence of agreement, that is, the use of suffixes and
prefixes simultaneously, and the simultaneous expression of subject and object
agreement.
The linguistic analysis of Georgian verbal morphology suggested in the previous
section relies on insights from Construction Grammar. Unfortunately, there are
currently no computational implementations of CG capable of handling complex
morphological systems. Bryant (2003) describes a constructional syntactic parser,
based on general principles of chart parsing. However, this parser cannot yet handle
morphological segmentation, and adapting it for Georgian would require substantial
revision.
Fortunately, FST tools for computational morphology have advanced to the point
where they can handle some aspects of non-concatenative morphology. The next
section briefly describes the approach in Beesley & Karttunen (2003) and what makes it
a possible candidate for modelling at least a subset of Georgian verbal morphology.
3.2 Xerox Finite-State Morphology Tools
Beesley & Karttunen (2003) present the state-of-the-art set of tools for creating
finite-state morphological models. The book is accompanied by implementations of
the two Xerox languages: xfst (designed for general finite-state manipulations) and
lexc (designed more specifically for defining lexicons). Since our goal was to reproduce
morphotactic rules of word formation rather than the structure of the lexicon, xfst
was used.
Xfst provides all of the basic commands for building up single or two-level finite-
state networks (i.e., transducers), such as concatenation, intersection, and so forth.
In addition, xfst has several built-in shortcuts that make network manipulation
easier, such as various substitution commands. Xfst distinguishes between words of a
natural language (composed of single characters) and multi-character symbols, used
in our model to indicate morphosyntactic properties such as person or number. Each
completed arc in a finite-state network compiled using xfst represents a mapping
between a set of morphosyntactic and semantic properties (on the upper side) and a
full word form that realises those properties (on the lower side).
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