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<Paper uid="C92-3128">
  <Title>Accenting and Deaccenting: a Declarative Approach</Title>
  <Section position="3" start_page="0" end_page="0" type="metho">
    <SectionTitle>
2 From Focus to Accent
</SectionTitle>
    <Paragraph position="0"> In focus-accent theory, metrical trees are used to represent relative prominence of nodes with respect to pitch accent. Whether a given node is accented or not is accounted for in terms of the focus/non-focus distinc tion.</Paragraph>
    <Paragraph position="1"> For example, a pitch accent on book in the phrase read a book may be accounted for by assuming the metrical structure (5).</Paragraph>
    <Paragraph position="3"> read a book In (5), the entire phrase is marked +F(ocus), iodicating that it is to be interpreted as a &amp;quot;new&amp;quot; or otherwise important addition to the discourse. The relation between the focus-marker and a pitch accent on book is mediated by the labels w(eak) and s(trong), and formally accounted for by the following  recursivc rule: 2 Accent Rule For each node X, X is accented if a. X is marked +F, or b. X is strong, and the node immediately dominating X is accented.</Paragraph>
    <Paragraph position="4">  marked +F, thus indicating the upper bound of what is sometimes called the &amp;quot;focus set&amp;quot;. Baart (1987) assumes that the metrical labeling of a structure is determined by syntactic/thematic properties of phrases such as specification and complementation. More generally, we assume that &amp;quot;arguments&amp;quot; which are not deaccented are strong. For example, in (i) the NP a book is an argument of the verb read. Also, a determiner takes a noun as an argument. In a PROS-3 grammar, one must make this explicit by writing rules such as those in (6).</Paragraph>
    <Paragraph position="6"> in such rules, (X/Y) or (Y\X) serves to indicate that Y is an argument of X. If we ignore deacccenting, argument structure directly determines the geometrical properties of the metrical tree, and we may read (X/Y) or (Y\X) as weak-stron.q or strongweak, respectively. 3 Also, a PROS-3 grammar must indicate which nodes are eligible for focus (normally, all major phrasal categories). If a node is eligible for focus, it must either be accented or deaccented. Words which are typically deaccented are specified as such in a lexicon. In our implementation, a binary-branching metrical tree is used as the central datastructure, and the relation between focus and accent is defined by using sharing variables, which may becmne instantiated to a value &amp;quot;true&amp;quot; (:=accented)or &amp;quot;false&amp;quot; (=&amp;accented), or remain unspecified (=not accented). The following definitions are used to implement accenting: 4</Paragraph>
    <Paragraph position="8"/>
    <Paragraph position="10"> deaccented(X).</Paragraph>
    <Paragraph position="11"> The statement accented(X) may be used to assign accent to a node, or to verify that the node is acccented. The staternent strong (X, Y), which reads &amp;quot;the strong node of X is Y&amp;quot; implements condition b of the Accent Rule above by unifying the values for accent of X and Y. The statement deaccented(X) succeeds if tile value for accent of X is instantiated to &amp;quot;false&amp;quot;, and fails otherwise, so it may be used as a test. Simi.</Paragraph>
    <Paragraph position="12"> larly, the statement not deaccented(X) may be used to test whether it might be possible to assign accent to X, but will not instantiate any values. Finally, the statement :focus(X) is used to assign accent to those nodes marked by the grammar writer as &amp;quot;eligible for focus&amp;quot;, unless they have been deacccented.</Paragraph>
  </Section>
  <Section position="4" start_page="0" end_page="0" type="metho">
    <SectionTitle>
3 Default Accent
</SectionTitle>
    <Paragraph position="0"> Consider again the sentences in (1), (2) and (3), and observe that when the NP the book is replaced by the pronoun it, pitch accent appears to &amp;quot;shift&amp;quot; from the NP to the most deeply embedded verb, read, of which it is an argument. Any differences between En glish, Dutch and German seem to be strictly a matter of syntax. Assuming appropriate phrase-structure rules, such as (6)a and b, this is reflected in the corresponding metrical tree. The metrical structure of the verb-phrase of (1)a, is a strictly right-branching structure which is uniformly labeled as weakstrong. The metrical trees corresponding to the verb phrases of (2)a and (3)a, shown in  In order to account for the b-sentences of (1), (2) and (3), in which a (deaccented) pronoun replaces NP, it seems that all that is needed is a reversal of the weak-strong labeling of the VP-node. To this end, Baart (1987) assumes the following rule:  Condition: B is deaccented In PROS-3, this rule is implemented as a filter, called STP, wtfich takes as input a syntactic structure assigned by the parser, and produces as output a metrical tree. A typical invocation might be:</Paragraph>
  </Section>
  <Section position="5" start_page="0" end_page="0" type="metho">
    <SectionTitle>
VP-&gt;(V/NP) =&gt; Prosody,
</SectionTitle>
    <Paragraph position="0"> focus (VP).</Paragraph>
    <Paragraph position="1"> Using the definitions of section 2, STP is defined by the following set of rules: ~ ~'l'ake note that we are rather frivolous in using the slash-notation to encode both argument structure and metrical structure, though, of course, the two are distinct. That is, the metrical tree does not replace argument structure, but is merely its realization in the domain of sentence prosody.</Paragraph>
    <Paragraph position="2"> AcrEs DE COLING-92, NAlVl'l!s, 23-28 AO\[~-r 1992 8 6 7 PRec. OF COLING-92, NANTES, AUG. 23-28, 1992</Paragraph>
    <Paragraph position="4"> strong(Z, Y).</Paragraph>
    <Paragraph position="5"> Cases a and c implement Default Accent, whereas b and d represent the &amp;quot;normal&amp;quot; case.</Paragraph>
  </Section>
  <Section position="6" start_page="0" end_page="0" type="metho">
    <SectionTitle>
4 Rhythmic Deaccenting
</SectionTitle>
    <Paragraph position="0"> Rhythmic factors provide a second source of deaccenting phenomena. They apply to structures such as (9), representing (4)c from section 1, and (10), representing the Dutch sentence &amp;quot;er is op VEEL plaatsen REGEN voorspeld&amp;quot; (there is in MANY places RAIN predicted), meaning: it has been predicted that it will rain in many places.</Paragraph>
    <Paragraph position="1">  op reel plaatsen regen Although the pitch accent patterns implied by these structures are well-formed, there is a strong preference for deaceenting nice in (9) and plaatsen in (10). In order to account for these phenomena, we assume the following optional rule (adapted from Baart 1987):</Paragraph>
  </Section>
  <Section position="7" start_page="0" end_page="0" type="metho">
    <SectionTitle>
RHYTHM RULE
</SectionTitle>
    <Paragraph position="0"/>
    <Paragraph position="2"> A B C h B C In this rule, brackets indicate a substructure which may repeated zero or more times. A further requirement is that nodes A, B and C are not deaccented.</Paragraph>
    <Paragraph position="3"> The Rhythm Rule differs from Default Accent in that it is not a local rule: its structural change, tile weak-strong reversal of A and B, is dependent ell the presence of a node C whose weak sister-node dominates A and B in a rather complex manner. One way to implement such context-sensitive rules in a declarative framework, is to use feature percolation. Space does not permit us to work out the implementation in full detail (there are also some additional requirements to be met), but the following should give the reader some idea.</Paragraph>
    <Paragraph position="4"> First, we add a new case to the STP-filter above, implementing the structural change of the Rhythm Rule, and marking the resulting structure with a feature annotation indicating that the Rhythm Rule has &amp;quot;applied&amp;quot;:</Paragraph>
    <Paragraph position="6"> not deaccented(X), not deacccented(Y), strong(Z, X), Z:rhytlm_rule === true. Next, we make sure that this feature is percolated upwards in weak-strong configurations, and blocked wherever necessary in order to filter out over-generation.</Paragraph>
  </Section>
  <Section position="8" start_page="0" end_page="0" type="metho">
    <SectionTitle>
ACRES DE COLING-92, NANTES, 23-28 AOt3T 1992 8 6 8 PROC. OF COLING-92, NANTES, AUG. 23-28, 1992
5 Conclusion
</SectionTitle>
    <Paragraph position="0"> As emphasized above, PROS-3 is a language-independent system for deriving sentence prosody in a text-to-speech system. This is true, of course, only to the extent that focus-accent theory and its major rules are universals of linguistic theory. Clearly, the proof of the pudding is in the eating. At IPO, PROS-3 is currently being evaluated for I)utch, using a grammar of about 125 rules ai,d a lexicon of some 80,000 word forms derived from the CELEX lexical database. Also, we are working on grammars and lexicons of comparable size and scope for English and German, and PROS-3 is used in the POLYGLOT-project for several F, uropean languages.</Paragraph>
    <Paragraph position="1"> Although preliminary results are encouraging, there are also problems which need mention. First, tim focus/non-focus distinction is modelled by rather crude heuristics (i.e. taking each major phrase as a candidate for focus, deaeeenting of pronouns etc. by lexical specification). It would be nice if something more flexible and &amp;quot;discourseaware&amp;quot; could be built in. Second, we have deliberately kept the PROS-3 grammar formalism rather simple (Mlowing only atomic syntactic categories), so we could guarantee fairly efficient processing, tlowever, simple context-free rules do not disambiguate very well. Third, simple rules cannot fully take into account verb subcategorization. As a result, it is sometimes impossible to make the distinction between arguments and nonarguments, which is crucial to the metrical rules. So, what we need to do, is find an optimal compromise between sophistication of syntactic analysis and efficiency of processing. We think that PROS-3 is the right tool to do this.</Paragraph>
  </Section>
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