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<?xml version="1.0" standalone="yes"?> <Paper uid="P87-1001"> <Title>TEMPORAL ONTOLOGY IN NATURAL LANGUAGE</Title> <Section position="4" start_page="0" end_page="0" type="metho"> <SectionTitle> 2. Temporal and Aspectual Categories </SectionTitle> <Paragraph position="0"> Utterances of English sentences can, following Vendler, be classified into temporal/aspecmal types on the basis of the tenses, aspects and adverbials with which they can cooccur (cf.</Paragraph> <Paragraph position="1"> Dowry, 1979). This &quot;espocmal type&quot; refers to the relation to other happenings in the discourse that a speaker predicates of the particular happening that their utterance describes. Thus an utterance of Harry reached the top is usually typical of what we will call a &quot;culmination&quot; -- informally, an event which the speaker views as accompanied by a transition to a new state of the world. This new state we will refer to as the &quot;consequent state&quot; of the event. Harry hiccupped is not usually viewed by speakers as leading to any specific change of state. It typifies what we call &quot;point&quot; expressions, that is punctual events whose consequences are not at issue.</Paragraph> <Paragraph position="2"> Similarly, Harry climbed typifies what we will call for obvious reasons a &quot;process&quot;: such utterances describe an event as extended in time but not characterised by any particular conclusion or culmination. In contrast. Harry climbed to the top typically describes a state of affah~ that also extends in time but that does have a particular culmination associated with it at which a change of state takes place. We classify such an utterance as a &quot;culminated process&quot;. Finally, Harry is at the top typically describes a state.</Paragraph> <Paragraph position="3"> Thus we can interpret Vendler as saying that a part of the meaning of any utterance of a sentence is one of a small number of temporal/aapectual profiles distinguished on a small number of dimensions. They can be summarized as in Figure It is important to be clear that this claim concerns sentences used in a conte~, sense-mearLings of sentences or verbs in isolation are usually compatible with several (or even all possible) Vendlerian profiles, as Dowry and Verkuyl have pointed out hence the frequent use of the word &quot;typically&quot; above. The details of this taxonomy and the criteria according to which utterances can be categorised are therefore less important than 1 Readen familiar with Vendler's work will realise that we have changed his terminology. We have done so both for notational convenience and to avoid the considerable confusion that has arisen concerning the precise meaning of the old terms.</Paragraph> <Paragraph position="4"> The ice melted completely Max worked in the garden Alice played the piano John knows French He was in the kitchen Hg~el the observation that each pri~tive entity of a given type, such as the culmination-event of Har~'s reaching the top, carries intimations of other associated events and states, such as the process by which the culmination was achieved, and the consequent state that followed. What linguistic devices like tenses, aspects, and temporal/aspectual adverbials appear to do is to transform entities of one type into these other &quot;contingently&quot; related entities, or to turn them into composites with those related entities.</Paragraph> <Paragraph position="5"> The temporal/aspecmal ontology that underlies these phenomena can be defined in terms of the state-transition network shown in Figure 2. The semantics of tenses, as-pecmal auxiliaries and temporal adverbials is defined in terms of functions which map categories onto other categories, and having the important characteristic of &quot;coez~ing&quot; their argument to be of the appropriate type. Both the possibilities for coercing an input proposition, and the possibilities for the output category. are defined by the transition net. In addition, the felicity of a particular transition is conditional on support from knowledge and context.</Paragraph> <Paragraph position="6"> Consider, for example, the combination of a culminated process expression with a for-adverbial, as in (3) Sue played the sonata for a few minutes.</Paragraph> <Paragraph position="7"> A for.adverbial coerces its input to be of the process variety. According to the network in Figure 2, such a transition is felicitoos if the culmination point associated with the event of p/ay/ng the sonata is &quot;stripped off'. As a result, there is no implication in (3) that Suefln/shed playing the sonata.</Paragraph> <Paragraph position="8"> Another routz through the network is possible in order to account for examples with for-adverbials: the culminated process, like any other event, can be viewed as an unstructured &quot;point&quot;. A transition to turn it into a process then results in an iteration of occurrences at which Sue plays the sonata. This route through the network seems to be ruled out for (3) because it finds no support in our knowledge about sonatas and about how long they typically last. It does result, however, in a likely interpretation for a sentence ~ke (4) Sue played the sonata for about eight hours.</Paragraph> <Paragraph position="10"> Not all aspecmal/temporal adverbials expressing a time span have the same functional type. /n-adverbials, for example, coerce their input to be a culminated process expression. This means that combination with a culmination expression requires the transition to be made to the culminated process node.</Paragraph> <Paragraph position="11"> According to the aspe~mal network in Figure 2 this transition is a felicitous one ff the context allows a preparatmy process to be associated with the culmination, as in (5): (5) Laura reached the top in two hours.</Paragraph> <Paragraph position="12"> The in-adverbial then defines the length of this preparatory period.</Paragraph> <Paragraph position="13"> Since the arcs describe what the world has to be like for transitions m be made felicitously, it is obvious that there are expressions that will resist certain changes. For example, it will be hard to find a context in which an in-adverbial can be combined with a culmination expression Ytke Harry accideraally spilled his coffee, since it is hard to imagine a context in which a preparatory process can be associated with an involuntary act.</Paragraph> <Paragraph position="14"> A similar problem arises in connection with the following example: (6) John ran in a few minutes The process expression John ran has to be changed into a culminated process expression before combination with the in-adverbial is possible. One way in which the network in Figure 2 will permit the change from a process to a culminated process is ff the context allows a culmination point m be associated with the process itself. General world knowledge makes this rather hard for a sentence like John ran, except in the case where John habitually runs a particular distance, such as a measured mile. If the in-adverbial had conveyed a specific duration, such as in four minutes, then the analysis would make sense, as Dowty has poimed out. However, the unspecific in a few minutes continues to resist this interpretation.</Paragraph> <Paragraph position="15"> However, another route is also possible for (6): the process of John running can be made into an atomic point' and thence into a culmination in its own right. This culmination can then acquire a preparatory process of its own -- which we can think of as preparing to run -. to become the culminated process which the adverbial requires. This time, there is no conflict with the content of the adverbial, so this reading is the most accessible of the two.</Paragraph> <Paragraph position="16"> Progressive auxiliaries coerce their input to be a process expression. The result of the application is a progressive state, which describes the process as being in progress. This means that, when a culmination expression like reach the top is used with a progressive, a transition path has to be found from the culmination node to the process node. According to the transition network, this involves first adding a preparatory process to the culmination, and then stripping off the culmination point.</Paragraph> <Paragraph position="17"> As a result, the progressive sentence only describes the preparation as ongoing and no longer asserts that the original culmination even occurred. There would be no contradiction in continuing (7) Harry was reaching the top asin (8) Harry was roaching the top but he slipped and fell before he got there.</Paragraph> <Paragraph position="18"> * As Moens & Steedman (1986) point out, the fact that according to the present theory, progressives coerce their input to be a process, so that any associated culmination is su'ipped away and no longer conuibutes to truth conditions, provides a resolution of the &quot;imperfective paradox&quot; (Dowry 1979), without appealing to theory-external consmaets like &quot;inertia worlds&quot;. A porfect, as in (9) Harry has reached the top refers to the consequent state of the culminetion. It requires its input category to be either a culmination or a culminated process, and maps this expression into its consequent state. Informal evidence that it does so can be obtained by noticing that perf~ts are infelicitous if the salient consequences are not in force. The most obvious of these consequences for (9) is that Hahn still be at the top, although as usual there are other possibilities. null Since the transition network includes loops, it will allow us to define indefinitely complex temporal/aspectoal categories, like ti~ one evoked by the following sentence: (10) It took me two days to play the &quot;Minute Waltz&quot; in less than sixty seconds for more than an hour.</Paragraph> <Paragraph position="19"> The culminated process expression play the Minute Waltz can combine sn'aightforwardly with the in-adverbial, indicating how long it takes to reach the culmination point of finishing playing the Mimae Waltz. Combination with the for.adverbial requires this expression to be mined into a process - the most obvious route through the network being that through the point node. The resulting culminated process expression describes the iterated process of playing the Minute Waltz in less than $ix~ seconds as lasting for more than an hour. The expression it took me..., finally, is like an in-adverbial in that it is looking for a culminated process expression to combine with. It finds one in the expression to play the Minute Waltz in less than sixty seconds for more than an hour but combination is hampered by the fact that there is a conflict in the length of time the adverbials describe. In the case of (10), the whole culminated process is instead viewed as a culmination in its own right (via the path through the point node). Knowledge concerning such musical feats then supplies an appropriate preparatory process which we can think of as practicising. The adverbial/t took me two days then defines the temporal extent of this preparatory process needed to reach the point at which repeatedly playing that piece of music so fast for such a considerable length of time became a newly acquired skilL This basic framework thus allows for a unified semantics of a wide variety of aspectual adverbials, the progressive, the perfect, and iterative expressions in English. It is also used to explain the effect of bare plurals and certain varieties of negation on the overall temporal structure of discourse (Moens forthcoming).</Paragraph> <Paragraph position="20"> All of the permissible transitions between aspectual categories illustrated in Figure 2 appear to be related to a single elementsry contingency-based event structure which we call a &quot;nucleus&quot;. A nucleus is defined as a structure comprising a culmination, an associated preparatory process, and a consequentstate, hcanberepresented~.orially as in~gure3. 2 preparatory process consequent state</Paragraph> <Paragraph position="22"> Any or all of these elements may be compound: the preparation may consist of a number of discrete steps, for example the stages of climbing, having lunch or whatever, leading to the culmination of reaching the top. The consequent state may also be compound. Most importantly, we shall see that it includes the further events, if any, that are in the same sequence of contingently related events as the culmination.</Paragraph> <Paragraph position="23"> Similarly, the culmination may itself be a complex event such as the entire culminated process of climbing a mountain.</Paragraph> <Paragraph position="24"> (In this case, the associated preparatory process and consequant state will be quite different ones to those internal to the culminated process itself.) The device is intended to embody the proposal that when we hear about an event like climbing a moun~a/n in conjunction with some coercive aspectuzl category which forces it to undergo a transition, then the alternatives that are available are: a) to decompose the core event into a nucleus and to make a transition to one of the componants, such as the prepuratory activity of climbing or to the consequent state of having climbed the mountain; or b) to treat the entire event as a culmination, to c(m~oose it into a nucleus with whatever preparation and consequences the context provides for the activity of climbing a mountain, and to make the transition to either one of those.</Paragraph> <Paragraph position="25"> We further claim that those are the on/y alternatives.</Paragraph> <Paragraph position="26"> The concept of a nucleus not only explains the Iransitions of Figure 2, but also provides an answer to the question raised in the introduction concerning the apparent vagaries in the meaning of when-clauses.</Paragraph> </Section> <Section position="5" start_page="0" end_page="4" type="metho"> <SectionTitle> 3. When-clauses </SectionTitle> <Paragraph position="0"> The aspects and temporal/aspecmal adverbials considered above all act to modify or change the aspecmal class of the core proposition, subject to the limits imposed by the network in Figure 2, which we claim is in turn determined by the organisation of episodic memory. However. tenses and certain other varieties of adverbial adjuncts have a rather different character. Tense is widely regarded as an anaphoric category.</Paragraph> <Paragraph position="1"> requiring a previously established temporal referent. The referent for a present tense is usually the time of speec.~ but the referent for a past tense must be explicitly established.</Paragraph> <Paragraph position="2"> Such a referent is usually established using a second type of &quot;temporal&quot; adverbial, such as once upon a time. attire o'clock last Saturday, while I was cleaning my teeth, or when I woke up this morning.</Paragraph> <Paragraph position="3"> Most accounts of the anaphoric nature of tense have invoked Reichenbach's (1947) trinity of underlying times, and his concept of the &quot;positional&quot; use of the reference time which he 2 A similar ~ent structure is proposed by Passonneau (1987).</Paragraph> <Paragraph position="4"> called &quot;R&quot;. Under these accounts (reviewed in Steedman, 1982), the adjuncts establish a reference time to which the reference lime of a main clause and subsequent same-tensed clauses may attach or refer, in much the same way that various species of full noun phrases establish referants for pronouns.</Paragraph> <Paragraph position="5"> However, in one respect, the past tense does not behave like a pronotm. Use of a pronoun such as &quot;she&quot; does not change the referent to which a subsequent use of the same pronoun may refer, whereas using a past tense may. In the following example. the teml~al reference point for sentence (b) seems to have moved on from the time established by the adjunct in (a): (II) a. At exactly five o'clock, Harry walked in.</Paragraph> <Paragraph position="6"> b. He sat down.</Paragraph> <Paragraph position="7"> This fact has caused theorists such as Dowry (1986), Hinrichs (1984) and Partee (1984) to stipulate that the ref~,~,ce time autonomously advances during a narrative. However. such a stipulation (besides creating problems for the theory vis-~i-v/s those narratives where reference time seems not to advance) seems to be unnecessmT, since the amount by which it advances still has to be determined by context. The concept of a nucleus that was invoked above to explain the varieties of aspecmal categories offers us exactly what we need to explain both the fact of the advance and its extent. We simply need to assume that a main clause event such as Harry walked in is interpreted as an entire nucleus, complete with consequent state, for by definition the consequent state includes whatever other events were contingent upon Harry walking in, including whatever he did next. Provided that the context (or the heerer's assumptions about the world) suppolls the idea that a subsequent main clause identifies this next contingent event, then it will provide the temporal referent for that main clause.</Paragraph> <Paragraph position="8"> In its ability to refer to entities that have not been explicitly mentioned, but whose existence has merely been implied by the presence of an entity that has been mentioned, tense appears more like a definite NP like the mus/c in the following example than like a p~o,~oun, as Webber (1987) points out.</Paragraph> <Paragraph position="9"> (12) I went to a party last night. The music was wonderful.</Paragraph> <Paragraph position="10"> A similar move is all that is required to explain the puzzle concerning the apparent ambiguity of when-clauses with which the paper began. A when-clause behaves rather like one of those phrases that are used to explicitly change topic, like and your father in the following example from Isard, (1975): (13) And your father, how is he? A when-clause introduces a novel temporal referent into focus whose unique identifiability in the bearer's memory is similarly presupposed. However, again the focussed temporal referent is an entire nucleus, and again an event main clause can attach itself anywhere within this structure that world knowledge will allow. For example, consider the example (1) with which we began (repeated here): (14) When they built the 39th Street bridge...</Paragraph> <Paragraph position="11"> (a) ...a local architect drew up the plans.</Paragraph> <Paragraph position="12"> Co) ...they used the best materials.</Paragraph> <Paragraph position="13"> (c) ...they solved most of their traffic problems.</Paragraph> <Paragraph position="14"> Once the core event of the when-clause has been identified in memory, the hearer has the same two alternatives described before: either it is decomposed into a preparatory process, a culmination and a consequent state, or the entire event is ueated as itself the culmination of another nucleus. Either way, once the nucleus is established, the reference time of the main clause has to be situated somewhere within it - the exact location being determined by knowledge of the entities involved and the episode in question. So in example (a) the entire culminated process of building the bridge becomes a culmination (via a path in Figure 2 which passes through the &quot;point&quot; node) which is associated in a nucleus with preparations for, and consequences of, the entire business, as in Figure 4: they prepare they have built to build the bridge The drawing up of the plans is then, for reasons to do with knowledge of the world, situated in the preparatory phase.</Paragraph> <Paragraph position="15"> In example (b), in contrast, the building of the bridge is decomposed into a quite different preparatory process of building, a quite different culmination of completing the bridge end some consequences which we take to be also subtly distinct f~rom those in the previous case, as in Figure 5. The use of the best materials is then, as in (a), situated in the preparatory process - but it is a different one this time.</Paragraph> <Paragraph position="16"> they build they have completed but pragmatics demands that the main clause be situated somewhere in the consequent state of building the bridge.</Paragraph> <Paragraph position="17"> Thus, a main clause event can potentially be situated anywhere along this nucleus, subject to support f3&quot;om knowledge about the precise events involved, But example (2) is still strange, because it is so hard to think of any relation that is supported in this way: (15) #When my car broke down, the sun set The when-clause defines a nucleus, consisting of whatever process we can think of as leading up to the car's break-down, the break-down itself and its possible or actual consequences. It is not clear where along this nucleus the culmination of the sun set could be situated: it is not easy to imagine that it is a functional part of the preparatory process typically associated with a break-down, and it is similarly hard to imagine that it can be a part of the consequent state, so under most imaginable circumstances, the utterance remains bizarre.</Paragraph> <Paragraph position="18"> The constraints when places on possible inteqa~etations of the relation between subordinate and main clause are therefore quite strong. First, general and specific knowledge about the event described in the when-clause has to support the association of a complete nucleus with it. Secondly. world knowledge also has to support the contingency relation between the events in subordinate end main clause. As a result, many constructed examples sound strange or are considered to be infelicitous, because too much context has to be imported to make sense of them.</Paragraph> <Paragraph position="19"> In all of the cases discussed so far, the main clause has been an event of some variety. When the main clause is stative, as in the following examples, the effect is much the same. That is to say, the when-clause establishes a nucleus, end the stative is asserted or ,-,ehed wherever world knowledge permits within the nucleus. The only difference is that statives are by definition unbounded with respect to the reference time that they are predicated of, end outlast it. It follows that they can usually fit in almost anywhere, end therefore tend not to coerce the when-clause, or to induce the causal/contingent interpretalions that we claim characteriso the corresponding sentences with events as main clauses: (16) When they built that bridge ..l was still a young lad.</Paragraph> <Paragraph position="20"> ...my grandfather had been dead for several years.</Paragraph> <Paragraph position="21"> ...my aunt was having an affair with the milkman.</Paragraph> <Paragraph position="22"> ...my father used to play squash.</Paragraph> <Paragraph position="23"> However, world knowledge may on occasion constrain the relation of a stative main clause, and force it to attach to or describe a situation holding over either the preparatory process or the consequent state of the subordinate clause, as in the following examples (cf. Smith 1983): (17) When Harry broke Sue's vase, ...she was in a good mood.</Paragraph> <Paragraph position="24"> ...she was in a bad mood.</Paragraph> </Section> <Section position="6" start_page="4" end_page="5" type="metho"> <SectionTitle> 4. Towards a Formal Representation </SectionTitle> <Paragraph position="0"> We have argued in this paper that a principled end unified semantics of natural language categories like tense, aspect and aspectual/temporal adverbials requires an ontology based on contingency rather than temporality. The notion of &quot;nucleus&quot; plays a crucial role in this ontology. The process of temporal reference involves reference to the appropriate part of a nucleus, where appropriateness is a function of the inherent meaning of the core expression, of the coercive nature of co-occurring linguistic expressions, end of particular end general knowledge about the area of discourse.</Paragraph> <Paragraph position="1"> The identification of the correct ontology is also a vital preliminary to the construction and management of temporal databases. Effective exchange of information between people and machines is easier if the data structures that are used to orgenise the information in the machine correspond in a natural way to the conceptual structures people use to organize the same information. In fact, the penalties for a bad fit between data-structures and human concepts are usually crippling for any attempt to provide natural language interfaces for data base systems. Information extracted from natural language text can only be stored to the extent that it fits the preconceived formats, usually resulting in loss of information. Conversely.</Paragraph> <Paragraph position="2"> such data structures cannot easily be queried using natural language if there is a bad fit between the conceptual structure implicit in the query and the conceptual structure of the database. null The &quot;contingency-based&quot; ontology that we are advocating here has a number of implications for the construction and management of such temporal databases. Rather than a homogeneous database of dated points or intervals, we should partition it into distinct sequences of causally or otlun~vise contingently related sequences of events which we will call &quot;episodes&quot;, each leading to the satisfaction of a particular goal or intention. This partition will quite incidentally define a partial temporal ordering on the events, but the primary purpose of such sequences is more related to the notion of a plan of action or an explanation of an event's occurrence than to anything to do with time itself.</Paragraph> <Paragraph position="3"> It follows that only events that are continganfly related necessarily have well defined temporal relations in memory.</Paragraph> <Paragraph position="4"> A first atxempt to investigate this kind of system was reported by Steedman (1982), using a program that verified queries against a database structured according to some of the principles outlined above. These principles can be described using Kowalski's event-calculus (Kowalski & Sergot 1986). In this f~amework, there are primitives called events, the occurrence of which usually implies the existence of periods of time over which states hold. In the terms of the present paper, these &quot;events&quot; are either &quot;points&quot; or &quot;culminations&quot; (depending on whether they are in fact associated with consequent states see section 2). For example, in the world of academic promolions which Kowalski and Sea'got take as an example, an evant description like John was promoted from the rank of lecturer to the rank of professor is a culmination which implies that there was a period of time, ended by this event, during which John had the rank of lecturer, and there is a period of time, started by that same event, during which John had the rank of professor.</Paragraph> <Paragraph position="5"> The events in the event calculus are given unique identifiers, but are not necessarily associated with absolute time. Moreover, they can be partially ordered with respect to each other, or occur simultaneously. Events themselves may also be described only partially;, later information can be added when it becomes available. These features, which they share with the corresponding primitives in a number of other formalisms, such as those of McDermott (1982), Allen (1984) and Lansky (1986), an constitute an advance over temporal representation formalisms based on the situation calculus (McCarthy & Hayes 1969)o Although Kowalski's events are undecomposable points or culminations, they can be used to describe extended events such as our processes, in terms of a pair identifying their starting point and to the point at which they stop (in the case of processes) or their culmination (in the case of culminated processes). This means that a process expression like John ran will introduce two events, one indicating the start of the process and one indicating the endpoint. Just like the point events considered by Kowalski and Sergot, these events have certain properties or states associated with them. The starting-point of the process referred to by uttering John ran marks the beginning of a progressive state that we refer to when we use a progressive like John is running, a state which is terminated by the corresponding endpoint event.</Paragraph> <Paragraph position="6"> This duality between events and states (which was also exploited in Steedman, 1982), is very useful for representing the kind of ontology that we have argued natural language categories reflect. But one shortcoming of Kowalski's event calculus is the absence of other than temporal relations between the events. The best worked out event-based model that takes into account causal as well as temporal relations is Lansky's (1986). The representation she presents is based on GEM (Lamsky & Owieki 1983), a tool for the specification and verification of concurrent programs. GEM retries events and explicitly represents both their causal and temporal relations.</Paragraph> <Paragraph position="7"> It also provides mechanisms for structuring events into so-called &quot;locations of activity&quot;, the boundaries on these locations being boundaries of causal access - as in our episodes. In Lansky (1986), the GEM tool is used to build event-based knowledge representations for use in planners. She suggests the use of three accessibility relations: temporal precedence (<), causality or contingency (@). and simultaneity ($).</Paragraph> <Paragraph position="8"> These relations have the following properties:</Paragraph> <Paragraph position="10"> Because we follow Lansky in making the causality/contingency relation @ intransitive, we avoid certain notorious problems in the treatment of when-clauses and perfects, which arise because the search for possible consequences of an event has to be restricted to theftrs~ event on the chain of contingencies. Thus, when (18a) and (b) are asserted, it would be wrong to infer (c): (18) (a) When John left. Sue cried (b) When Sue cried, her mother got upset (c) When John left, Sue's mother got upset The reason is exactly the same as the reason that it would be wrong to infer that Sue's mother got upset because John left, and has nothing to do with the purely temporal relations of these events. It should also be noted that the notion of causality or contingency used here (in line with Lansky's proposals) is weaker than that used in other representation schemes (for example that of McDermott 1982) in that causality is here decoupled from eventuality: if an event A stands in a causal relation to event B, then an occurrence of A will not automatically lead to an occurrence of B: John laying the foundations of the house is a prereclulSlto for or enables him to build the walls and roof but does not &quot;cause&quot; it in the more Iraditional sense of the word and doe~ not automatically or inevitably lead to him building the walls.</Paragraph> </Section> <Section position="7" start_page="5" end_page="5" type="metho"> <SectionTitle> 5. Conclusion </SectionTitle> <Paragraph position="0"> Many of the apparent anomalies and ambiguities that plague current semantic accotmts of temporal expressions in natural language stem from the assumption that a linear model of time is the one that our linguistic categories are most directly related to. A more principled semantics is possible on the assumption that the temporal categories of tense, aspect, aspecmal adverbials and of propositions themselves refer to a mental representation of events that is smJcmred on other than purely temporal principles, and to which the notion of a nucleus or contingently related sequence of preparatory process, goal event and consequent state is central.</Paragraph> <Paragraph position="1"> We see this claim as a logical preliminary to the choice of any particular formal representation. However, certain properties of the event-based calculi of Kowalski and Sergot. and of Lansky. seem to offer an appropriate representation for a</Paragraph> </Section> <Section position="8" start_page="5" end_page="5" type="metho"> <SectionTitle> 3 A Prolog program incorporating the above exmnsion to the </SectionTitle> <Paragraph position="0"> event calculus is under construction and will be presented in Moens (forthcoming).</Paragraph> <Paragraph position="1"> semantics of this kind.</Paragraph> </Section> class="xml-element"></Paper>