In Case of Case…
Wednesday, May 6th, 2009A recently hot topic of discussion in the Ubiquity i18n realm has been how to deal with strongly case-marking languages. As we continue to make steady progress, this is one of remaining open questions which we must decide as a community how to tackle in Parser 2.
Introduction
Grammatical case is a marking on nouns that express grammatical function. Not all languages exhibit case. In many of the Indo-European languages we hope to bring Ubiquity to, case is realized as a suffix.1
Here’s a classic example of case from Latin. (Line 2 is the gloss of 1, line 4 of 3.)
1 2 3 4 | canis virum momordit dog=sg.NOM man=sg.ACC bite=3sg.perfect vir canem momordit man=sg.NOM dog=sg.ACC bite=3sg.perfect |
Example (1) is “the man bit the dog,” while example (3) is “the dog bit the man.” The only difference, as you see in the gloss, is that the nouns canis and vir are marked with different case endings in the two sentences. By marking the nouns with different cases (here, nominative and accusative), their semantic roles in the sentence—which is the the biter and which is the bitee—can be identified unambiguously. (Their positions are also switched in these examples but in reality Latin has a very free word order—the same sentences with other word orders including OSV or VSO are also common.)
At first glance, strongly case-marked languages may look like a godsend for identifying the semantic roles of arguments.2 If we can easily and unambiguously recognize arguments’ cases to put them in their appropriate semantic roles, this could simplify processing as well as make Ubiquity input follow a natural syntax for such languages. Unfortunately, there are some significant challenges which must be overcome in order to make the processing of case-markers worthwhile.
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Note that when linguists talk about “case,” they could be referring to two different (though related) concepts: case (lowercase) is the observed pattern of affixes on nouns which indicate grammatical function, while Case (uppercase) refers to a theoretical (formal) feature of syntactic objects—certain lexical items “assign Case” or “receive Case” and its mismatches were ruled out in GB syntax by the Case Filter. You’ll find GB linguistics papers referring to “case” when discussing Mandarin Chinese, for example, a language that doesn’t have any overt case (lowercase) and you’ll know immediately that this usage is an uppercase Case case. In this blog post I’ll be dealing primarily with the former descriptive notion. ↩
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When I refer to “strongly case-marking languages,” I am referring to languages with a non-trivial inventory of cases (not just nominative, accusative, and genitive) and where a noun phrase’s case is not reflected on determiners. For example, German is excluded by this definition as case is realized exclusively on articles and there is no need to find and parse the noun head itself to identify its case—more information on German is in the section “finding the edges.” ↩