...Keller
This WWW\ document is largely based on three publications: Evans & Gazdar 1996, Keller 1995, and Keller 1996. For citation purposes, please refer to the published papers, where possible, rather than the web pages you are reading.
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...illustrate
Node names and atoms are distinct but essentially arbitrary classes of tokens in DATR. In this this document (and elsewhere) we distinguish them by a simple case convention - node names start with an uppercase letter, atoms do not.
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...atoms)
This is an approximation since it ignores the role of global contexts - see Section 4, below.
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...verb
And hence also the extensional version, Word1:<syn cat> = verb
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...context
Strictly speaking, the query node and path form just the initial global context, since as we shall see in Section 3.2.2 below, the global context can change during inheritance processing.
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...lexemes
Linguistically, the analysis is still not abstract enough since it fails to encode the morphotactic generalisation that, by default, an inflected English word consists of a root optionally followed by a suffix. Such generalisations are easy enough to state in DATR but would entail more elaboration of our running example than its expository purpose requires.
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...etc.
Our orthographic representations here presuppose some basic ``spelling rules'', thus love ed is spelt loved, love ing is spelt loving and mow en is spelt mown. If we had chosen to represent roots and suffixes as letter sequences rather than as atoms then it would have been possible to implement the necessary spelling rules in a finite state transducer written in DATR itself. See, for example, that presented in Section 6.3, below.
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...follows
Orthographically, the form does could simply be treated as regular (from do s). However, we have chosen to stipulate it here since, although the spelling appears regular, the phonology is not, so in a lexicon that defined phonological forms it would need to be stipulated.
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...arbitrary
Formally, we require them to be finite classes, but this is not of great significance here.
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...zero
DATR makes a distinction between a path not having a value (i.e., being undefined) and a path having the empty sequence as a value:

NUM:
<two> ==
<one> == one.

In this example, NUM:<one> has the value one, NUM:<two> has the empty sequence as its value, and NUM:<three> is simply undefined.

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...as
A descriptor containing an evaluable path may include nested descriptors which are either local or global. Our use of the local/global terminology always refers to the outermost descriptor of an expression.
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...values
We continue to oversimplify matters somewhat. The meaning of a node depends on the global context, and a node thus really denotes a function from global contexts to partial functions from paths to values. Though important, this point is tangential to the issue addressed here.
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...counterpart
NONFUNC3 perhaps comes closest, but adding statements about extensions of either <a> or <b> quickly breaks the illusion that the two are in some sense ``unified''.
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...verbs
Bear in mind that the following are not synonymous

Come:<syn> == INTRANSITIVE:<>.
Come:<syn> == INTRANSITIVE.

since the latter is equivalent to

Come:<syn> == INTRANSITIVE:<syn>.

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...arise
The past participle extensions here are purely for the sake of the formal example - they have no role to play in the morphological description of English (but cf. French where past participles inflect for gender and number).
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...ignored)
Thus, for example, the path <mor plur acc> is a gratuitous extension of the path <mor plur> for English common nouns since the latter are not differentiated for case.
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...language
Undeclared variables are similarly assumed to range over the full set of atoms. Some implementations may also include implicit definitions of more restricted variables, such as $integer.
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...hold
In this and subsequent examples in this section, syntactic objects (e.g., love, <mor root>) are used to stand for their semantic counterparts under F (i.e., 51#51, 52#52, respectively).
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...mechanism
The problem is partially overcome in E&G 1989a by making use of a second kind of DATR sentence (the extensional sentence) which effectively provides an implicit reference to global context. However, this approach relies on the overly-restrictive assumption that there is at most one global inheritance descriptor on the right of each definitional sentence
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...you)
For clarity, this FST does not exploit default inheritance to capture the 50% overlap between the subject and object pronoun paradigms. See Gazdar (1992) for a version that does.
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...kinds
Radically lexicalist frameworks, which lack any construction-specific grammatical rules outside the lexicon, do not restrict the use of lexical rules to ``cyclic'' phenomena. Thus, for example, Evans et al. (1995) report the use of DATR to formulate a lexical rule for wh-questions in LTAG , inter alia.
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...DATR
Evaluable paths are not essential in this domain: thus Kilgarriff (1993) does not employ them in his DATR analysis of verbal alternations in the context of an HPSG lexicon, although he does use the standard encoding of argument lists.
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...construction
Since our purpose here is expository, we have deliberately kept the analysis to minimum. Dealing with the semantics of passive, for example, involves more of the same rather than any issue of principle.
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...cherry
The example is due to Kilgarriff (1995) who shows that the kind of polysemy exhibited by cherry applies generally to fruit trees and can thus be specified at a higher node in the lexical network, removing the need for stipulation (as in our example) at the Cherry node, the Apple node, and so on. Kilgarriff & Gazdar (1995) also present an extended example showing how DATR can be used to encode the regular and subregular polysemy associated with the crop, fibre, yarn, fabric and garment senses of words like cotton and silk.
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...senses
For perspicuity, we provide these in DATR -augmented English here. But in a serious treatment they could just as well be given in a DATR -encoding of the lambda calculus, say (as used in Cahill & Evans 1990, for example).
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...hooves
See also the dreamt/dreamed verb class discussed by Russell et al. (1992, 330-331).
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...rest
In this connection, see the discussion of ``closure definitions'' in Andry et al. (1992, 259-261).
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...value
This approach is due to recent unpublished work by Jim Kilbury. He has shown that the same DATR theorems can have their values realised as conventional attribute-value matrix representations, Prolog terms, or expressions of a feature logic, simply by changing the fine detail of the transducer employed.
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...languages
Anonymous FTP to ftp.cogs.sussex.ac.uk and directory /pub/nlp/DATR provides access to various DATR\ implementations, the example archive, and some relevant papers and documentation.
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...etc.)
An alternative formulation is to start with a known value and path, and the task is to infer the appropriate nodes.
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Copyright © Roger Evans, Gerald Gazdar & Bill Keller
Wed Feb 26 12:00:02 GMT 1997