Representation

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# Representation - PowerPoint PPT Presentation

Representation. A farmer wants to move himself, a hunrgry silver fox, a hungry, fat goose, and a sack of tasty grain across a river. Unfortunately, his boat is so tiny he can move only one of his possessions across on any trip. What is he to do?. Fox, Farmer, Goose, Grain.

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## PowerPoint Slideshow about 'Representation' - erika

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Presentation Transcript
Representation
• A farmer wants to move himself, a hunrgry silver fox, a hungry, fat goose, and a sack of tasty grain across a river. Unfortunately, his boat is so tiny he can move only one of his possessions across on any trip. What is he to do?
Fox, Farmer, Goose, Grain
• 5 minute break for solving the problem
• Keep track of how you solve the problem (think about how you think to solve the problem)
Representation
• Look at the representation in figure 2.1.
• Graph like representation
• Nodes: A safe distribution of entities on both banks of the river
• Edges: connect nodes separated by a single boat trip
• Solution: draw a line from start state to end state
Analysis
• How many nodes?
• How many safe nodes?
Representation is key
• Once represented using nodes and links, problem is simple to solve
Representation
• A lexical part: What symbols are allowed in your vocabulary/lexicon
• A structural part: constraints on how symbols can be arranged
• A procedural part: access procedures to create, modify descriptions
• A semantic part: associates meaning with description
Semantic Nets
• Structural: Each link connects a tail node to a head node
• Semantic: Nodes and links denote application specific entities
Good Representations
• Example of a good representation in object identification
• Identify an object as belonging to a class
• Basic Method: Describe and Match
• Describe Object (using a “good” representation)
• Match to library of object descriptions
• Return closest match
Object Identification
• Feature based object identification
• Feature extractor, extracts easily identifiable object features (area, perimeter, hole count, hole area, …)
• Values of these features locate the object in an n-dimensional feature space (an object occupies a feature point in feature space)
• Compare the distance of unknown object’s feature point to library of known (idealized) object’s feature points. The most likely identity is determined by smallest distance.
• Read Chapters 1 and 2
• Assignment 1 considers Missionaries and Cannibals is available, due Feb 4.
• Back of book contains hints
• Need help, talk to me
3 Missionaries 3 Cannibals
• Three cannibals and three missionaries are standing on the west bank of a river. A boat is available that will hold either one or two people. If the missionaries are ever outnumbered -- on either bank or in the boat -- the cannibals will eat them. Your job is to design a program (come up with a representation and implement a search algorithm) that will get everyone across the river to the east bank safely.
Burglar and combination lock
• Generate a combination
• Test if it opens the safe
• Consider 6 digit combination
• 10^6 combinations
• 10^6/2 combinations on average to find correct combination, 3/min  16, 24 hr weeks
Generate and Test
• Powerful problem solving method
• Until a satisfactory solution is found or no more solutions can be generated
• Generate the candidate solution
• Test the candidate solution
• If an acceptable solution is found, announce it; otherwise announce failure
Dendral
• Good generator – complete, nonredundant, only generates structures arising from known formula
• Tester – Spectrogram comparator
Terminology
• State (of a system): Description of a system that is sufficient to determine the future
• State space: Each node denotes a state, and each link denotes a possible one-step transition from one state to another
State Space
• A state space is a representation
• That is a semantic net
• In which
• Nodes denote states
• Links denote transitions between states
• Initial state, current state, goal state