Categories – relations or individuals? • What are the differences in representing collie as a relation vs. an individual? • As a relation: collie(lassie) • Can reason only about members of the category collie, not about the category (FOPC only allows terms, not predicates, as arguments of predicates: cannot make true/false statements about predicates): goodWithKids(lassie). • As an individual: ISA(lassie,collie) • Can make statements about both categories and individual members of categories: • goodWithKids(lassie) • goodWithKids(collie)
Reification • Reification is the technique we used to make collie an individual; reification is sometimes called objectification. • ISA is a member-class relationship • ISA(lassie, collie) • AKO (A Kind Of) is a subclass-superclass relationship: • AKO(collie, dog) • AKO(dog, mammal) • AKO(mammal, animal)
Events – relations or individuals? • We face the same question for events as we did for categories. • Should we represent events as relations or as individuals? • Looking at syntax it seems that representing the event as a relation is natural (think of subcategorization frames). • But, this implies we can’t reason about events! • Take the same approach as with categories: reify!
Basic problem (p. 524-525) • Examples with the verb to eat: • I ate. • I ate a turkey sandwich. • I ate a turkey sandwich at my desk. • I ate at my desk. • I ate lunch. • I ate a turkey sandwich for lunch. • I ate a turkey sandwich for lunch at my desk. • All describe an event of eating. • What is a reasonable representation?
Events as relations • Suppose we decide that events should be represented as relations. • Q: What is the arity (# arguments) of the predicate? • A: It is different in different examples! • Eating1(Speaker) • Eating2(Speaker, TurkeySandwich) • Eating3(Speaker, TurkeySandwich, Desk) • Eating4(Speaker, Desk) • Eating5(Speaker, Lunch) • Eating6(Speaker, TurkeySandwich, Lunch) • Eating7(Speaker, TurkeySandwich, Lunch, Desk)
Reasoning problem • While we can build such representations, they do not possess the desired characteristics. • For example, we cannot reason with these representations to learn that they all describe the same type of event (an eating event): • Eating1 Eating2 Eating3 Eating4 Eating5 Eating6 Eating7 • Can solve this problem by introducing meaning postulates, such as, • w,x,y,z Eating7(w,x,y,z) Eating6(w,x,y) • Such a solution does not scale well (since these have to be explicitly encoded into knowledge base).
Additional problems • Assumes that underlying event always has four arguments (eater, food, meal, location) • but surely you can eat outside of regular meal times • Can’t express that two (partial) descriptions are about the same event: • w,x Eating(Speaker, w, x, Desk) • w,x Eating(Speaker, w, Lunch, x) • w Eating(Speaker, w, Lunch, Desk)
Reification of event is a better solution • Compare the following two representations of “I ate a Turkey sandwich” • w,x Eating(Speaker, TurkeySandwich, w, x) • e ISA(e,Eating)Eater(e,Speaker)Eaten(e,TurkeySandwich) • Advantages: • “There is no need to specify a fixed number of arguments for a given surface predicate, rather as many roles and fillers can be glued on as appear in the input.” [p. 527] • “No more roles are postulated than are mentioned in the input.” [p. 527] • “The logical connections among closely related examples is satisfied without the need for meaning postulates.” [p. 527]
Time and events • Consider the following three examples (cf examples on page 528) • I will arrive in Buffalo. • I am arriving in Buffalo. • I arrived in Buffalo. • They all describe an event of arriving: • e ISA( e, Arriving ) Arriver( e, Speaker ) Destination( e, Buffalo ) • What makes them different is the time of the event.
Representing the time of an event • e,i,t ISA(e,Arriving) Arriver(e,Speaker) Destination(e,Buffalo) IntervalOf(e,i) EndPointOf(i,t) Precedes(Now,t) • e,i,t ISA(e,Arriving) Arriver(e,Speaker) Destination(e,Buffalo) IntervalOf(e,i) MemberOf(i,Now) • e,i,t ISA(e,Arriving) Arriver(e,Speaker) Destination(e,Buffalo) IntervalOf(e,i) EndPointOf(i,t) Precedes(t,Now)
Representing time • Reichenbach (1947) • E is the event time • R is the reference time • U is the utterance time • See diagram on page 530.
Simple past (R=E < U) Present (R=E=U) Simple future (R=U < E) Past perfect (E<R<U) Present perfect (E<R=U) Future perfect (U<E<R) I ate. I eat. I will eat. I had eaten. I have eaten. I will have eaten. Examples
Aspect • The aspect of an event describes: • whether event is ongoing or completed • whether it occurs at a point in time or over an interval of time • whether its completion results in a change in the state of the world • Events are classified as one of: • state • activity • accomplishment • achievement
States – I • “States are like snapshots of the world at a given instant. They lack a natural culmination or end point, and their subject is perceived not as an agent (as doing something) but as an experiencer (as experiencing something).” “Meaning and Grammar: An Introduction to Semantics” by Chierchia and McConnell-Ginet, p. 353
States – II • Examples: • John is drunk. • John knows Latin. • Diagnostics: • not good in progressive: • *John is being drunk. • *John is knowing Latin. • not good in imperative: • *Be drunk! • *Know Latin!
Activities – I • “Activities share with states the property of lacking a natural culmunation. Yet they are agentive in that they typically involve a subject doing something. They cannot in general be viewed as instantaneous snapshots of the world.” [ibid, p. 353]
Activities - II • Examples: • John is kicking. • John is studying. • Diagnostics: • fine in progressive (see above!) • fine in imperatives: • Kicker harder! • Study longer!
Accomplishments – I • “accomplishment expressions describe events that have a natural end point and result in a particular state.” [p. 532] • Examples [p. 532]: • He booked me a reservation. • United flew me to New York.
Accomplishments – II • Diagnostic: stop [p. 532]: • I stopped living in Brooklyn. [activity] • She stopped booking my flight. [accomplishment] • Inferences? • I lived in Brooklyn. • but not: She booked my flight. (intended state was not reached) • Diagnostic: temporal adverbials [p.533] • *I lived in Brooklyn in a year. [activity] • She booked a flight in a minute. [accomplishment]
Achievements – I • “[Achievement expressions] are similar to accomplishments in that they result in a state. […] Unlike accomplishments, achievement events are though of as happening in an instant, and are not equated with any particular activity leading up to the state.” [p. 533]
Achievements – II • Examples: • She found her gate. • I reached New York. • Diagnostic: temporal adverbial [p. 533] • I lived in New York for a year. [activity/accomplishment] • *I reached New York for a few minutes. [achievement] • Diagnostic: stop [p. 533] • I stopped booking my flight. [accomplishment] • *I stopped reaching New York. [achievement]