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<Paper uid="C96-1074">
  <Title>Distributedness and Non-Linearity of LOLITA's Semantic Network</Title>
  <Section position="4" start_page="436" end_page="438" type="metho">
    <SectionTitle>
3 SemNet: LOLITA's Semantic
</SectionTitle>
    <Paragraph position="0"> Network SomNet; IHLs b(`-e\]t designed spociti(:a, lly for la.rgc scMc NI, I&amp;quot;,. This so(:tJot~ desct'il)0s some of Lhc core aspcot;s needed lk)r this discussion. Sere-Net; is ++ graph of nodes ~md arcs which degan I)o rea.d/Lraversed in oil, her (lir0cLion. Assochfl.od wiLh 0ach noddeg ~Lrc controls. (lotfl, rots hold sl;ru&lt;:-Lurod inform;d,ion al)otH; Lhe, ir nodo, s. t/ccauso Lhcy a.ro inLernal t() cinch noddeg l;hoy axe llOt+ sub,iecL (wil, h rcspecl, Lo ScinNoL) t,o l, he .'-;cax(:h prol)orl;ics mcntionod proviously.</Paragraph>
    <Paragraph position="1"> 'l'hcrc are, Lhroe Lyl)oS o\[7 nodes: o.ntil,io.q, ov(`-nl,s 'n,o,.o .,-o th,.o.</Paragraph>
    <Paragraph position="2"> typos of directed aros: subj0cl;, object and acl, ion u which (:ml I)o re~d/Lravcrsed in degil,hor diredegLion. ~&amp;quot;l'he nmnes of I.hcse. m'(:s shotl\](l neiLher I)c (:oH+\['tlSCd wii;\[l gheir gr;,tulnh+tgi(:kt |COUllCel'l:,~l+l't, ~ Ol' wil,}l t;\]lc case mmlysis of (l&amp;quot;ilhnorc, 1,968). 'l'he.y can be LhoughL</Paragraph>
    <Paragraph position="4"> l?igure 1: Figure 1: (a) SemNet event for &amp;quot;Every farmer that owns a donkey beats it.&amp;quot; (b) SemNet epistemic event for &amp;quot;Roberto believes that every farmer owns a donkey.&amp;quot; Only event nodes can have a subject, object or action. Only action nodes can be an action for an event node. A control for each node specifies its type. E3 in Figure l(a) asserts that two entities (FAP~MER1 and DONKEY1) are in an beating relationship. The subject/object arcs ensure that it is understood that farmers beat donkeys and not vice versa.</Paragraph>
    <Paragraph position="5"> A fundamental principle of the design is that concepts are not reduced to primitives. The meaning of any node is detined in terms of its relationship with other nodes, so ultimately each node is only fully defined by the whole semantic network.</Paragraph>
    <Paragraph position="6"> It shonld be noted that the event nodes can be the subject or object, of another event so that SemNet is 'propositional' in the sense used by (Kumar, 1993).</Paragraph>
    <Section position="1" start_page="436" end_page="436" type="sub_section">
      <SectionTitle>
3.1 Quantification
</SectionTitle>
      <Paragraph position="0"> A problem for networks is to ensure that relationships refer to concepts unambiguously (Woods, 1991). For example without reference information, E3 in figure l(a), could mean any of: a farmer beats a donkey, all farmers beat a donkey, all farmers beat a (the same) donkey, or all farmers beat all donkeys. In SemNet this ambiguity is resolved by attaching the following quantification a labels to arcs: * Universal U refers to the instances of the concept and says that all the instances of the concept are involved in relationship specified by the event.</Paragraph>
      <Paragraph position="1"> * Individual I refers to the concept as a whole and says that it is involved in the relationship specified by the event.</Paragraph>
      <Paragraph position="2"> alt should be noted that this paper presents a simplified account of the quantification scheme used in SemNet. The full scheme is described in (Short, 1996). * Existential E refers to the instances of the concept, but the instance involved depends on the particular instance of some other universally quantified concept which is involved in the event.</Paragraph>
      <Paragraph position="3"> Existential arcs can be thought of as existentially quantified variables in First Order Logic (FOL), which are necessarily scoped by some universal. To represent an existential that is not scoped by a universal we use the individual ra.nk. 'thus for E2 in figure l(a), the donkey thai; is involved depends on the farmer. This could be interpreted 4 into FO1, as:-Beats(x, y)) 'lb demonstrate how SemNet can represent complex expressions, consider the well known donkey sentence: &amp;quot;Every farmer that owns a donkey beats it.&amp;quot; Of course to capture this unambiguously the meaning has to be agreed. It is assumed that it is correctly represented by the FOL  statement:-A l o, k y(y) A</Paragraph>
      <Paragraph position="5"> SemNet represents this as shown in figure l(a).</Paragraph>
      <Paragraph position="6"> The event 1!;2 is an 'observing' event, it represents the assertion of the donkey sentence) l'h is a 'defining' event used to build the complex concepts I&amp;quot;ARMER1 (farmers that own (and so beat) donkeys) and DONKEY1 (donkeys that are owned by these Nrmcrs). For clarity the events linking hierarchies of farmers and donkeys have been written as spec (for specialisation).</Paragraph>
    </Section>
    <Section position="2" start_page="436" end_page="438" type="sub_section">
      <SectionTitle>
3.2 Representation of Belief and
Intensional Knowledge
</SectionTitle>
      <Paragraph position="0"> It is important to emphasise that the information which is recorded within SemNet is intended to reflect the world as it is to be understood by the agent that uses the network. No claim is made that the representation reflects the world as it really is (if there is such a thing), nor even that the representation reflects some consensus view of the way the world is. Thus from an external view-point the concepts should be interpreted as intensional, ttowever from the agent's viewpoint, they  resents &amp;quot;farmers that own donkeys&amp;quot; so this formula is inferred by second (donkey sentence) formula, as would be expected.</Paragraph>
      <Paragraph position="1">  constitute the world it believes in, and thus may be either extensional or intensional. As it is cmnbersome to repeal; that we are dealing with the agent's belieN, this shall be taken as read in the rest of this section. Similarly, the agent will be referred to by the natne I, OI,ITA, as this is the only agent so far which uses SereNe,.</Paragraph>
      <Paragraph position="2"> It is possible for LOLITA to believe that another agent believes some relation to hohl. lib,: example, 1,OIXI'A may believe that &amp;quot;l{oberto believes that every l%rmer owns a donkey.&amp;quot;, see figure l(b). 1)istributedness requires that one may read igl and 1'32 independently front the other. Aceording to the description given so t%r, there is no difl%rence between the way 1';1 is represented when I,()M'I'A believes it, and when it; is there merely as a part of some other event which \[,()I,I'I'A believes (of course it could I)e both), q'hns it' 1'31 is read on its own, all that wouhl be said is that some agent potentially believes in the relation it expresses. To identify any such agent would require some form of search which would be inetficient as very often the agent will be l,()lJ'.l?A, l)istributedness ca.n be better exploited by using a control. A status control makes this distinction, it takes two va.lues: real (when I~OI,I'I'A believes in the event), and hypothetical (otherwise).</Paragraph>
      <Paragraph position="3"> Statements may either I)e made about concepts or about the things concepts rel&gt;r to. These eases need to be distinguished, l,'or example, con-sider the three concepts &amp;quot;the morning star&amp;quot;, the &amp;quot;evening star&amp;quot; and &amp;quot;Venns&amp;quot;. 'Phe nlorning star is the last p()int of light in the sky to disal)l)ear at dawn, the evening star is Lhe first l)oi,,t of lighL in the sky to appear at dusk, and Venus is a particMar planet of the solar system. Thus, Mthough they have the same extension they are different intensioually. Since the representation ret)resents different concepts I)y different nodes, there inust be a means to state that two coi, cepts reD,; to the same objeet. '\['his is done using an extensional synonym event to connect the concet)ts. The synonym event, has no e\[Dct on distributedness or non-linearity but affects topological dist~mce and deterrninism of search adversely.</Paragraph>
      <Paragraph position="4"> This price is justified as distinguishing intensional and extensionM concepts is important in many situations. For exert,pie, if one tells LOLH?A &amp;quot;I need a hammer&amp;quot;, one does not want her to answer that she has found a hammer: &amp;quot;the hammer that you need&amp;quot;. Such misunderstandings will occur unless the hammer is correctly understood as intensional and distinguished in the representation from extensional hammers. This is done using a 'tensional' control stating whether tile node has an extension in the world, an extension in some other franle of existence, such as Agatha Christie's fictional world where tile hamtner was the lnnrder weapon, or an unkuown extension. Not('. that 'tensionality' and belief are independent. A relation may be not only hypotheticM, but also inteusionM: &amp;quot;John believes he needs a hanlmer&amp;quot;.</Paragraph>
      <Paragraph position="5"> a.a Features exploiting {he search I)rOl)Oxtlo.s If controls were written as events, they would be ant-directional, involving an uni-directional sub ject or object arc, i.e. if a control rel&gt;rs to a node. of the network, there need not be any information on that node baek to the control. Such unidire(:tional events are beneficial to the (leterntinism of search since they restrict the number of arcs that can be traversed from any node. Controls represent a fltrther imln'Ovement on distributedness since they reduce the number of reqnired event nodes without Mfecting richness. The in~ formation expressed as controls is never re l~rred to by other events.</Paragraph>
      <Paragraph position="6"> Controls allow defaulting, which is illegal for the network, l)efaulting consists of assulning some fact, when no information of that fact's type is e.xpressed explicitly. This means that the infer-.</Paragraph>
      <Paragraph position="7"> marion expressed by some section of SereNe, can be unsound with re.spect to the fn\]l semanl,ic net.</Paragraph>
      <Paragraph position="8"> It might appear suHicient to check all the events attached to a node to determine whether a default al)l:)lies , but it; shouhl be remembered that events can also be inherited from far Ul) the inheritance hierarehy. Indeed, one of the practical advantages of distributedness is that it does away with the need of inheriting all a nodes 'ancestors' inR)rlnalion while allowing the benefits of a hierarchieal knowledge base.</Paragraph>
    </Section>
  </Section>
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