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<?xml version="1.0" standalone="yes"?> <Paper uid="E93-1020"> <Title>[Barwise and Cooper, forthcoming\] Jon Barwise</Title> <Section position="3" start_page="159" end_page="165" type="metho"> <SectionTitle> 2 Grammar and Implementation </SectionTitle> <Paragraph position="0"> The fragment contains sequences of sentences of a type similar to the ones given in Section 1. It includes sentence-final 'then', together with other temporal adverbials such as for-adverbials, frame adverbials (e.g, 'in July') and completive/n-adverbials (e.g., 'in two hours'). Sentence-initial 'then' and sentence-final 'at the time' and 'at the same time' are also included, although we do not discuss their analysis here. There is a range of verbs, transitive and intransitive, with various aspectual characteristics, and a range of noun types including count nouns, mass nouns, bare plurals, definite and indefinite NPs. Progressives are also included. We are thus concerned not merely with the analysis of 'then' but with matters of aspectual composition/modification and the distribution of temporal adverbials. Space does not permit us to describe the full system in detail. We will concentrate here on those parts of it that are particularly relevant to the analysis of 'then'.</Paragraph> <Paragraph position="1"> As the system is concerned with temporal matters, we have not built into it a treatment of pronominal anaphora. However, it is designed in such a way, as will shortly become clear, that it could be extended without undue difficulty to include pronoun anaphora, using a treatment based on that in (Johnson and Klein, 1986).</Paragraph> <Paragraph position="2"> The system parses sequences of sentences and produces representations for the required readings for SWe discuss in (Glasbey, msl) how 'at the time' behaves similarly to the part-of use of 'then' (but conveys only backgrounding and not elaboration), while 'at the same time' appears to be acceptable in cases where the second eventuality is not a part of the first, i.e., where it can be seen as forming a distinct or separate event. These are also included in the implemented grammar, but their treatment is not described here.</Paragraph> <Paragraph position="3"> sentence-final 'then'. It is based on a situation-theoretic grammar developed in (Cooper, 1991) and its computational implementation ProSit (Cooper, msl). ProSit is a definite clause grammar (DCG) with features. It parses single sentences and constructs syntactic and semantic representations expressed in situation-theoretic terms. We have extended it firstly to deal with sentences containing a range of tense and aspect constructions which were not present in Cooper's original fragment, and secondly to allow the processing of discourse. To enable us to do the former, we have built aspectual composition into the grammar using a theoretical approach based upon (Krifka, 1991) and described below. In order to process discourse, we have employed the technique known as 'threading', used by Johnson and Klein (1986), whereby discourse referents are carried from left to right among the constituents of a sentence, and from one sentence to the next.</Paragraph> <Paragraph position="4"> Extended Kamp Notation The grammar is expressed in a combined DRT/situation theoretic formalism, employing the Extended Kamp Notation (EKN) developed in (Barwise and Cooper, forthcoming). These authors use a box notation for situation-theoretic objects such as infons, situations and propositions, based upon the graphical notation of DRT (Kamp and Reyle, forthcoming). However, in EKN the boxes directly represent semantic objects, in contrast to DRT where the discourse representation structures (DRSs) are expressions of a language which require interpretation in a model. Nevertheless, EKN boxes look rather like DRSs. One important difference, however, is that EKN boxes may contain situations.</Paragraph> <Paragraph position="5"> In situation theory, infons (which can be thought of as items of information or &quot;possible facts&quot;) are supported by situations, which are parts of the world as individuated by agents. An infon consists of a relation 1deg with its argument roles filled by objects which may be individuals, parameters or other situation-theoretic objects. Propositions in EKN include objects of the form: sl climb(X,Y) which is the proposition that a situation S supports an infon climb(X,Y). 11 Situation-theoretic objects may have restrictions imposed on them. A proposition with restrictions is shown in Figure 1.</Paragraph> <Paragraph position="6"> The box in Figure 1 denotes an object only if the restrictions are true, i.e., in the above case, if X is 1degRelations are primitives in situation theory.</Paragraph> <Paragraph position="7"> llS, X and Y are parameters, denoted by capital letters in situation theory. A parameter is a partially-specified object.</Paragraph> <Paragraph position="8"> anchored to an individual named 'Emily' and Y to an individual named 'Ben Nevis'. R is the resource situation supporting information about the naming of individuals) 2 A proposition containing parameters is known as a parametric proposition. It is possible to abstract (simultaneously) over one or more parameters of a parametric proposition to give a type of the form shown in Figure 2.</Paragraph> <Paragraph position="9"> Once a parameter has been abstracted over, it effectively &quot;disappears&quot; and is no longer present in the type. What remains is the &quot;role&quot; corresponding to the abstracted parameter. These roles may be indexed however we choose (for example, by the natural numbers, by rl to r, as above, or by utterance situations as in (Cooper, 1991)).</Paragraph> <Paragraph position="10"> Cooper (ms2), in the development of situation-theoretic DRT (STDRT), sees a DRS as equivalent to the situation-theoretic type obtained by abstracting over the parameters of a proposition. The roles of such a type are equivalent to DRT discourse referents, and the infons correspond to the conditions of the &quot;main&quot; situationJ 3 The system parses both individual sentences and sequences of sentences forming a discourse. For a sentence such as: (lc) Emily climbed Ben Nevis.</Paragraph> <Paragraph position="11"> it produces a syntactic parse tree, together with a semantic representation in the form of a DRS/type as shown in Figure 3. The DRS/type is shown in slightly simplified form here. It will also contain in12See (Cooper, forthcoming) for further explanation. lsOf course there are no precise DRT equivalents of the situation and the restrictions.</Paragraph> <Paragraph position="12"> r, -->S, r2 --~X, rz -+ Y, r4 -+R, rs -+T sl formation about aspectual class etc., as discussed below. null Parsing of an individual sentence takes place in a top-down TM, left-to-right manner, causing a DRS/type like the one in Figure 3 to be gradually built up. The lexical entry for a verb introduces a &quot;skeletal&quot; (partially instantiated) type, and further information is added to this by the remaining constituents as parsing proceeds.</Paragraph> <Paragraph position="13"> Although there is no explicit mention of a &quot;time&quot; in (lc), the representation for this sentence (Figure 3) contains a parameter T corresponding to what we call the the &quot;occurrence time&quot; of the eventuality. This is the total temporal extent of the eventuality. Although inclusion of the occurrence time is not strictly necessary in the representation for a single sentence with no ETR, it will be needed when we come to process discourse. We will see shortly that stative verbs do not introduce occurrence-times into the representations, whereas non-stative ones do, unless they are presented with progressive aspect. null Now compare the representation produced for the sentence: (la) Emily climbed Ben Nevis in July.</Paragraph> <Paragraph position="14"> In this case, the system produces the DRS/type&quot; shown in Figure 4.</Paragraph> <Paragraph position="15"> Here we have a second temporal parameter T', corresponding to to the explicit temporal referent 'July'. Note that the role corresponding to this parameter is indexed by 'pr'. This indicates that this time referent, unlike the one corresponding to T, is phonologically realised in the utterance. This distinction will be important when we come to process 'then'. Here we are exploiting the possibility afforded by situation theory of being able to include information about the utterance in our semantic representations. 15 14However, top-down processing is not essential to the grammar, and a left-corner parser or chart parser could be used instead.</Paragraph> <Paragraph position="16"> tSWe have not taken the trouble here to mark non-</Paragraph> <Paragraph position="18"/> <Paragraph position="20"> is another kind of EKN proposition--one that does not involve a situation. It expresses the information that T and T' are of type E, where this is a type of two times such that the second includes or equals the first.</Paragraph> <Paragraph position="21"> Now let us consider the semantic representation for a discourse. This consists of a proposition which is the conjunction of the propositions introduced by the individual sentences. Abstraction is carried out over the conjoined proposition as a whole, giving a list of discourse referents/roles for the discourse processed up to a given point.</Paragraph> <Paragraph position="22"> Thus for (la, lg): (la) Emily climbed Ben Nevis in July.</Paragraph> <Paragraph position="23"> (lg) Fiona climbed Snowdon.</Paragraph> <Paragraph position="24"> we get the representation shown in Figure 5.16 Now let us consider the processing of discourse sequences containing sentence-final 'then'. Consider (la,lb): (la) Emily climbed Ben Nevis in July.</Paragraph> <Paragraph position="25"> (lb) Fiona climbed Snowdon then.</Paragraph> <Paragraph position="26"> The system parses (la), followed by (lb) as far as 'then'. At this point in processing, the representation built so far is that of Figure 5. The processing temporal discourse referents as phonologically realised, as this is not relevant to the analysis of 'then'--but it could of course be done.</Paragraph> <Paragraph position="27"> 16The representation for (la, lg) will also contain information about possible discourse relations between the two eventualities. We do not describe this feature of the system here except where it is relevant to 'then'. of 'then' causes the rules for ETR 'then' and part-of 'then' to be invoked in turn. The rule for ETR 'then' causes the system to &quot;look for&quot; a temporal referent indexed 'pr' in the list of discourse referents introduced by the processing of the discourse up to this point. This list of discourse referents is threaded from one sentence to the next (and from NP to VP within a sentence). In fact, what is threaded is not just the discourse referents but the overall DRS/type from the processing of the discourse up to this point. The threading is achieved at discourse level by means of the top-level rule of the grammar: dis(dis(SBar, Dis)),In, Out) --> sbar(SBar,Type .... ,In,Ned), dis(Dis,Ned,Out).</Paragraph> <Paragraph position="28"> The first argument to the predicate 'dis' is responsible for building the tree structure associated with the parse. The second and third arguments, the Prolog variables 'In' and 'Out', enable threading of discourse referents from the sentence just parsed to the remaining discourse. The input 'In' to the processing of sbar consists of the overall DRS/type built up from processing the discourse up to this point. This includes a list of discourse referents generated so far. The grammar rules at sbar level and below cause the overall DRS/type to be updated to give a new type 'Med', which is the input DRS/type to the processing of the remainder of the discourse. The 'Type' argument of sbar is the DRS/type obtained from parsing that individual sentence. The other arguments to sbar are not relevant to this discussion and have thus been omitted.</Paragraph> <Paragraph position="29"> Thus, at a given point in processing of discourse, the system can look for a temporal referent indexed 'pr'. Looking at Figure 5, we see that an appropriate temporal referent indexed 'pr' is present. The rule for ETR 'then' therefore succeeds, and a proposition is introduced to the effect that T2 is temporally included in T', i.e.</Paragraph> <Paragraph position="31"/> <Paragraph position="33"> This proposition is added to the restrictions of the lower box of Figure 5, to give the completed representation for (la, lb), which is not shown here for reasons of space. If there had been no such temporal referent marked 'pr' present, the rule for ETR 'then' would have failed.</Paragraph> <Paragraph position="34"> Now consider the part-of reading for 'then'.</Paragraph> <Paragraph position="35"> We saw earlier that this requires an appropriate discourse relation between the two described eventualities---one of either backgrounding or elaboration. Testing for whether an elaboration relation is possible requires world knowledge, and we have not attempted to build any of this into the system, although there appears to be no reason why this could not be done. The system in its present form therefore checks only for the background instance of the part-of relation.</Paragraph> <Paragraph position="36"> Backgrounding is possible if the second eventuality is either a state or if it is presented with progressive viewpoint. This means that, in order to test for backgrounding, the representations for individual sentences must contain information about the aspectual properties of the described eventualities-for example, whether an eventuality is a state or a non-state (event), and whether it is presented with simple aspect (external viewpoint) or progressive aspect (internal viewpoint). It is widely known that the aspectual properties of a described eventuality depend on certain properties of the verb 17 and also on other elements such as the referents of NP arguments. For example, the event described by: (5) Daniel climbed a mountain.</Paragraph> <Paragraph position="37"> is a Vendler accomplishment. Alternatively, we may characterise it in Krifka's terms as having the property +Q (quantized) or -CUM (non-cumulative), which are equivalent to the lack of a natural end-point or culmination. However, the event described by: (6) Daniel climbed mountains.</Paragraph> <Paragraph position="38"> is a Vendler activity, and in Krifka's terms has the property -Q/+CUM. Here we see what Krifka describes as a &quot;mapping&quot; from the properties of the NP object is to the properties of the event. The referent of 'a mountain' is +Q, and so is the event of (5). The referent of 'mountains' is -Q, and so is the event of (6). Such mapping from the properties of the object to the properties of the event only occurs for certain verbs, however--those where what Krifka calls the 17E.g. 'basic aspectual type' in Moens' terms (Moens, 1987) and semantic features in both Verkuyl's (1989) and Krifka's (1991) accounts.</Paragraph> <Paragraph position="39"> lSMore strictly the &quot;patient&quot;, as it is thematic roles and not grammatical roles that are important here.</Paragraph> <Paragraph position="40"> &quot;thematic relation&quot; between the object and the event has an appropriate property. One such property that enables this mapping is what he calls gradual patient. In such cases, there is an intuitive relationship between the &quot;progress&quot; of the object and the progress of the event. For example, in an eating event, the object is gradually consumed, and in a writing event, the object is gradually created. Both 'eat' and 'write', as well as 'climb' thus have thematic relations with the property gradual patient. Driving events do not, on the other hand, exhibit this correspondence between the progress of the event and the progress of the object. Thus the thematic relation between object and event for 'drive' does not have the gradual patient property, which explains why: (7) John drove the car.</Paragraph> <Paragraph position="41"> is +CUM/-Q even though 'the car' is -CUM/+Q. 19 In our EKN account we encode Krifka's properties of thematic relations as types of situations and individuals. For example, the lexical entry for 'climb' includes the following information:</Paragraph> <Paragraph position="43"> The grammar rules then make reference to this information. For example, the rule: vbar( .... ) --> v( .... ), np( .... ) contains a procedure which evaluates the Q-value of the predicate (vbar) according to the following algorithm: null If: The thematic relation between S and Y is of type GRAD-PAT Then: Set the Q-value of the predicate (vbar) to be the same as that of Y Otherwise: Set the Q-value of the predicate to -Q. The Q-value of the agent 2deg also affects that of the described eventuality. For example, the eventuality described by: (8) Emily climbed the mountain.</Paragraph> <Paragraph position="44"> is +Q, whereas that described by: (9) People climbed the mountain.</Paragraph> <Paragraph position="45"> is -Q. In (9), the -Q value of the agent is transferred to the event. In order to deal with such examples, the rule s(...) --> rip(...), vp(...) rule.</Paragraph> <Paragraph position="46"> Thus the representation constructed by parsing a sentence includes information about the aspectual properties of the described eventuality. These include the features +/-STATE and +/-Q as already described, together with +/-PROG depending on whether or not progressive aspect is present, and +/-PUNCT which distinguishes punctual and non-punctual events (corresponding to the difference between achievements and accomplishments). Let us now consider the representation from the processing of: (le) Fiona was a girl then.</Paragraph> <Paragraph position="47"> up to the point where 'then' is reached. This is given (in slightly simplified form) in Figure 6. Now suppose we are processing (lc,le): (lc) Emily climbed Ben Nevis.</Paragraph> <Paragraph position="48"> (le) Fiona was a girl then.</Paragraph> <Paragraph position="49"> The rule for part-of 'then' requires that the second eventuality is either a state or it is described with progressive viewpoint. The former is true in this case, so the conditions for part-of 'then' are satisfied. The representation obtained for (lc,le) is shown in Figure 7.</Paragraph> <Paragraph position="50"> The semantics of ~part-of' What exactly does it mean for the part-of (~) relation to hold between two eventualities? The idea is that if $2 ~ $1, then any infon which is supported by $2 is also supported by $1. In other words, $2 adds further information to S1, causing it to be more fully specified. Here we exploit the partiality of situation theory. Situations may be only partially specified: if we say that $1 supports ~, this does not tell us anything about what other information S1 does or does not support. It is thus possible for a later utterance to add further information about $1 and thereby specify it more fully. If the first utterance tells us that $1 supports the infon ~r, and the second tells us that $2 supports the infon 7&quot; and also that $2 <1 $1, then we know that $1 supports both a and v. This is straightforward enough for the elaboration case. We need to consider carefully what it means in a backgrounding case such as (la,le). According to our theoretical analysis, if an eventuality is backgrounded then it does not introduce an occurrence-time of its own. Instead, the backgrounded eventuality is of the same duration as that of the preceding event--it &quot;takes on&quot; the time of that event. 21 Thus, in the representation of (lc,le) in Figure 7, the backgrounded $2 has the same temporal extent as the event $1. This amounts to claiming that (le) describes only the part of the state that coincides with the preceding event. Of course we know that the state of Fiona's being a girl began before and continues after Emily's climb--there is a relationship of temporal inclusion between the &quot;total duration&quot; of the state and the event. But we are saying that those parts of the state that are before and after the event are not described but are inferred from our world knowledge about the duration of such states.</Paragraph> <Paragraph position="51"> Stative verbs are &quot;natural backgrounders&quot; in that they describe eventualities without making reference to the beginning and end points of the eventuality. They naturally describe a situation which can readily be seen as a temporal &quot;slice&quot; of a more prolonged situation. For this reason, in the lexical entries for stative verbs in our grammar, there is no mention of the occurrence-time of the state. Progressives usually behave in a similar way. When an event described with progressive viewpoint follows one with simple (perfective) viewpoint, the relation between them is normally one of backgrounding. The effect of progressive viewpoint is to present the event from an internal perspective. An event described with internal perspective is no longer temporally bounded--it does not have an occurrence-time of its own. Instead, its duration is that of the preceding event, just as in the stative case.</Paragraph> <Paragraph position="52"> If we define two instances of the part-of relation: . <1 bg for the backgrounding case * _ el for the elaboration case we can thus say: S2 ~ b s $1 ) T2 = Tz where T1,T2 are the temporal durations of $I and $2 respectively. And: S~ <l el $1 -'--+ T2 ___ T1 Thus, for the general <l relation:</Paragraph> <Paragraph position="54"> 21Evidence for this comes from an analysis of 'at the time' and 'at the same time'. See (Glasbey, ms2) for details.</Paragraph> <Paragraph position="55"> Finally, let us consider (la,lf): (la) Emily climbed Ben Nevis in July. (lf) Fiona was climbing Snowdon then. In this case, an ETR is present and the second sentence has progressive aspect. This means that the conditions for both ETI~ 'then' and part-of 'then' are met.Our grammar will thus cause two representations to be generated for (la, lf), corresponding to the two readings that we identified in Section 1.</Paragraph> </Section> <Section position="4" start_page="165" end_page="166" type="metho"> <SectionTitle> 3 General remarks </SectionTitle> <Paragraph position="0"/> <Section position="1" start_page="165" end_page="165" type="sub_section"> <SectionTitle> 3.1 Further Developments </SectionTitle> <Paragraph position="0"> The system parses sequences of any length, keeping track of all the discourse referents/roles introduced so far. Thus, as it stands at present, it will find a temporal referent for 'then', irrespective of how far back in the discourse that referent was introduced.</Paragraph> <Paragraph position="1"> It may be desirable to refine this in some way--for example, to disallow anaphoric reference to an ETR that is more than a certain &quot;distance&quot; back in the discourse. Also, the system at present finds only the most recently introduce temporal referent. This could easily be modified--for example, in order to allow it to produce a set of alternatives. However, it appears that we would need to take discourse structure into account here.</Paragraph> </Section> <Section position="2" start_page="165" end_page="166" type="sub_section"> <SectionTitle> 3.2 Relation to other accounts of temporal </SectionTitle> <Paragraph position="0"> reference It is important to consider how our analysis fits with other work on temporal reference in discourse, and how readily our treatment of 'then' could be incorporated into these accounts. Kamp and Reyle (forthcoming) present a DRT fragment which deals with temporal reference but does not include 'then'. In (Glasbey, forthcoming) and (Glasbey, 1992) we present a modification of Kamp and Reyle's fragment which incorporates our analysis of 'then'. We make the necessary distinction between what we call &quot;explicit&quot; and &quot;inferred&quot; times by allowing a temporal referent to be introduced only when an explicit temporal referent is present. If there is no ETR, only an event referent may be introduced. This enables us to produce the correct readings for 'then'. We consider the ST/DRT account given in the present paper to be preferable, however, in that situation theory allows us to express information about the utterance in a way that traditional DRT does not. This enables us to make precisely the distinction we need between whether or not a particular referent was phonologically realised in the utterance.</Paragraph> <Paragraph position="1"> Lascarides and Asher (1991) present an account of temporal reference where discourse relations between eventualities are deduced by means of defeasible reasoning. Their account is expressed in a version of DRT and preliminary investigations suggest that it could be extended to include 'then' in a similar way to the Kamp and Reyle fragment.</Paragraph> </Section> </Section> class="xml-element"></Paper>