Notes for November 11, 2002
Semantic Analysis
- Thematic Roles
- How do syntactic and lexical analysis fit in with semantic analysis?
- Lexical analysis
o How you get verbs from a sentence: ôHe at a frogِ € lexical anaysis € ôئHeئ is a pronounِ, ôئateئ is a verbِ, à
- Syntactic analysis
o Using the verb وateئ we retrieve a frame from memory and try to fill in the slots.
o A simple rule for finding the agent could be ôWhatever comes before وeatئ is the agentِ
- As a sentence becomes more complex, analysis becomes more difficult.
o For instance, ôThe frog was eaten by himِ
o The word before وeatenئ is not the agent.ل
o We could add more rules.ل However, the more rules we add the more the like lexical analysis this becomes.
o In order to add rules, we need a better lexicon:
o Now we can add a rule to the frame.
o Now we make sure that the thing before ôeatِ is animate.
- Step-by-step process for the two rule example:
1. Start with a sentence and find its verb (lexical analysis).
2. Use the verb to probe into memory and retrieve the relevant frame.
3. Look at each slot in order and if applicable apply rule 1.
4. Otherwise, look at rule 2 if applicable and call the syntactic analysis with the new lexicon.
More complex sentences
- Garden Path Sentence
o Syntactically correct but meaningless
o ôGreen ideas sleep furiouslyِ
- Sentences with multiple verbs:
o ôI bought a doll and put a pin in it because it replicated my lover who left me.ِ
- Ambiguous sentences:
o ôI saw the man on the hill with the telescopeِ
o وtelescopeئ could go with me, man, or hill
- Complex sentences require frame composition or extra knowledge
o The frame provides some context.
o To gain more context, we can use multiple frames or a script per paragraph.
؛ Memory is a reservoir of contexts
؛ retrieve context € context drives analysis
o If you add, ôI went for a walkِ after the telescope sentence, it disambiguates the owner of the telescope somewhat.ل It is unlikely that someone would walk with a telescope.
Scripts provide dependencies between frames:
- Preceding frame guides current frame.
- Vision has an analogous problem:
o Analyzing frames and scripts is analogous to analyzing images and videos in computer vision. You can get context from adjacent images.ل (temporal constraints)
Question in class: Why not use nouns instead of verbs to reference frames?
Answer: there are far fewer verbs in natural languages.
- The reference problem:
o ôJohn took Mike to an ice cream shop.ِ
o ôHe ordered butter rumِ (ambiguous: who ordered butter rum?)
o ôAs Mike was eating his ice cream (disambiguates: Mike must have ordered butter rum)
o In this case, we go back to a previous frame and fill in the agent ôMikeِ for ordering the butter rum.
o There must be a working memory to do this.ل (working memory is small and limited).
o
- Problems for working memory:
1. Keeping track of frames
2. How to keep track of unfilled slots or ambiguously filled slots
*Remember truth propagation networks (with a meta-reasoner)?
*Scripts
- Airport video example (how to use all that info to figure out who is acting suspiciously).
- Can use video scripts that define suspicious behavior
- Text:للللللللللللللللللللللللللللللللللللللللللللللللللللللللللللللل (Abstraction 1)
o I went to a fancy restaurant.لللللللللللللللل Frame 1
o I ordered veal filet mignon.لللللللللللللللل Frame 2
o It came burned.للللللللللللللللللللللللللللللللللل Frame 3
- Question:لللللللللللللللللللللللللللللللللللللللللللللللللللللللل Each frame provides context for rest
o Did Ashok leave a heavy tip?
- Abstraction 2:
o Use script for sequence of frames as context for each frame.
Example: Check email script
- Text:
o Zack logs on to machine
o He activates the mailer
o He checks his CoC email
o He then shakes his head, grunts, and gets up.
- Question:
o Did he receive CoC email?
- Script:
o Checks for favorite email first
o If there is mail, reads it
o If not, leaves the room
Humorà??
- Humor is telling a story that doesnئt meet expectations?