Amber Stubbs, SeoHyun Im, Roser Saurí, Marc Verhagen
Version 2, December 2006.
We consider main events within the scope of a sentence. With that in mind, we start by defining the basic notions at play: sentence, and event.
We adopt the notion of sentence standardly assume in the NLP community. That is, as the basic textual unit immediately above the phrase which ends with a terminal punctuation mark, such as: ., ?, or !. Example (1) contains two different sentences (delimited by the <s> tag), whereas example (2) has only one.
(1) <s>Australia has been independent since 1901.</s> <s>However, it still recognizes the British monarch as its head of state.</s>
(2) <s>Australia has been independent since 1901, but it still recognizes the British monarch as its head of state.</s>
Event is a cover term for predicates describing:
(3) 11,024 people were evacuated to 18 disaster relief centers.
(4) After these payments, about $225,000 will be available for the 20 million common shares outstanding.
Events can be denoted by verbs (reach, evacuate), adjectives (available, outstanding), or nouns (search, payment).
Events in text are annotated following TimeML annotation guidelines (Saurí et al., 2005:section 2.1.1). These guidelines cover problematic cases in detail, such as: light verb constructions, complex verb forms (with auxiliaries and/or polarity particles), phrasal verbs, predicative constructions, etc.
There will be only one main event per sentence.
Identifying the main event in a sentence that has only one event is trivial, since this automatically becomes the main event of that sentence.
In the case of sentences with multiple events (e.g., example 5), the main event will be determined following very shallow, syntactic-based criteria.
(5) ``We're expecting a major eruption,'' he said in a telephone interview early today.
Two different situations can be distinguished here:
The main event will be the event that is dominant syntactically. This apply to all kinds of subordination. Here, we list the most relevant for reference.
(6) It surprised me [that Gulshan Lake has so many little bugs and bacteria].
(7) He told reporters [(that) he had no message from Baghdad].
(8) Reporters asked President Bush [whether the interdiction would apply to food].
(9) The panel is investigating [who shot down Rwandan President Juvenal Habyarimana's plane on April 6, 1994].
(10) A war [that is supposed to help feed the desperate people of Afghanistan].
(11) Several neighbors heard [it happen].
(12) Her wife convinced [him to leave the country].
(13) I don't see things [getting as acrimonious as they do].
(14) He stayed behind because he couldn't speak French.
(15) So when Wong Kwan spent seventy million dollars for this house, he thought it was a great deal.
(16) There have been far more participants this year [than there were last year].
(17) He is about as old [as his father was at his age].
Two comments need to be made here. First, note that the main events selected here (participants, old) do not denote an event by themselves. They are however annotated as events following the TimeML annotation guidelines (Saurí et al, 2005), which specify that the copular verb be is never marked as event, but the head of their predicative complement instead.
Second, in (17) there are two phrases introduced by the conjunction as. The subordinated phrase is the second one.
(18)[The transaction] has been approved by Kyle's board.
(19) The new Essex County task force is delving [into the slayings of 14 black women].
(20) There was no independent confirmation [of the fact] by the government-run news agency.
(21) The agreement is subject [to shareholder and regulatory approval].
(22) A new Essex County task force began [delving Thursday into the slayings of 14 black women].
(23) The chip gives [wrong answers] for some mathematical calculations.
(24) [But over all, arrests were made in more than 60 percent of murder cases], he said.
(25) The rains caused the flood.
The main event will be the first one of the two coordinated events. Some coordinating conjunctions in English are: and, or, but, nor, yet, so, as well as, only, such that.
(26) He sold the property to five buyers [and] said he'd double his money.
(27) Australia has been independent since 1901, [but] like many Commonwealth nations it still recognizes the British monarch as its head of state.
(28) I had hoped to see her, [only] she did not come.
(29) The work started very hard, [such that] many people were injured.