Resolution

resolution steps are applied  to CNFcomplete for FOL

 

Initial State: Knowledge base (KB) of axioms and negated theorem in CNF

Operators: Resolution rule picks 2 clauses and adds new clause

Goal Test: Does KB contain the empty clause?

Branches of AI and Applications of AI

 Branches of AI

 

logical AI

What a program knows about the world in general the facts of the specific situation in which it must act, and its goals are all represented by sentences of some mathematical logical language. The program decides what to do by inferring that certain actions are appropriate for achieving its goals.

search

AI programs often examine large numbers of possibilities, e.g. moves in a chess game or inferences by a theorem proving program. Discoveries are continually made about how to do this more efficiently in various domains.

pattern recognition

When a program makes observations of some kind, it is often programmed to compare what it sees with a pattern. For example, a vision program may try to match a pattern of eyes and a nose in a scene in order to find a face. More complex patterns, e.g. in a natural language text, in a chess position, or in the history of some event are also studied. These more complex patterns require quite different methods than do the simple patterns that have been studied the most.

representation

Facts about the world have to be represented in some way. Usually languages of mathematical logic are used.

inference

From some facts, others can be inferred. Mathematical logical deduction is adequate for some purposes, but new methods of non-monotonic inference have been added to logic since the 1970s. The simplest kind of non-monotonic reasoning is default reasoning in which a conclusion is to be inferred by default, but the conclusion can be withdrawn if there is evidence to the contrary. For example, when we hear of a bird, we man infer that it can fly, but this conclusion can be reversed when we hear that it is a penguin. It is the possibility that a conclusion may have to be withdrawn that constitutes the non-monotonic character of the reasoning. Ordinary logical reasoning is monotonic in that the set of conclusions that can the drawn from a set of premises is a monotonic increasing function of the premises. Circumscription is another form of non-monotonic reasoning.

common sense knowledge and reasoning

This is the area in which AI is farthest from human-level, in spite of the fact that it has been an active research area since the 1950s. While there has been considerable progress, e.g. in developing systems of non-monotonic reasoning and theories of action, yet more new ideas are needed.

learning from experience

Programs do that. The approaches to AI based on connectionism and neural nets specialize in that. There is also learning of laws expressed in logic.

planning

Planning programs start with general facts about the world (especially facts about the effects of actions), facts about the particular situation and a statement of a goal. From these, they generate a strategy for achieving the goal. In the most common cases, the strategy is just a sequence of actions.

epistemology

This is a study of the kinds of knowledge that are required for solving problems in the world.

ontology

Ontology is the study of the kinds of things that exist. In AI, the programs and sentences deal with various kinds of objects, and we study what these kinds are and what their basic properties are. Emphasis on ontology begins in the 1990s.

heuristics

A heuristic is a way of trying to discover something or an idea imbedded in a program. The term is used variously in AI. Heuristic functions are used in some approaches to search to measure how far a node in a search tree seems to be from a goal. Heuristic predicates that compare two nodes in a search tree to see if one is better than the other.

genetic programming

Genetic programming is a technique for getting programs to solve a task by mating random Lisp programs and selecting fittest in millions of generations. 

 

Applications of AI:

game playing

You can buy machines that can play master level chess for a few hundred dollars. There is some AI in them, but they play well against people mainly through brute force computation--looking at hundreds of thousands of positions. To beat a world champion by brute force and known reliable heuristics requires being able to look at 200 million positions per second.

speech recognition

In the 1990s, computer speech recognition reached a practical level for limited purposes. Thus United Airlines has replaced its keyboard tree for flight information by a system using speech recognition of flight numbers and city names. It is quite convenient. On the the other hand, while it is possible to instruct some computers using speech, most users have gone back to the keyboard and the mouse as still more convenient.

understanding natural language

Just getting a sequence of words into a computer is not enough. Parsing sentences is not enough either. The computer has to be provided with an understanding of the domain the text is about, and this is presently possible only for very limited domains.

computer vision

The world is composed of three-dimensional objects, but the inputs to the human eye and computers' TV cameras are two dimensional. Some useful programs can work solely in two dimensions, but full computer vision requires partial three-dimensional information that is not just a set of two-dimensional views. At present there are only limited ways of representing three-dimensional information directly, and they are not as good as what humans evidently use.

expert systems

A "knowledge engineer'' interviews experts in a certain domain and tries to embody their knowledge in a computer program for carrying out some task. How well this works depends on whether the intellectual mechanisms required for the task are within the present state of AI. When this turned out not to be so, there were many disappointing results. One of the first expert systems was MYCIN in 1974, which diagnosed bacterial infections of the blood and suggested treatments. It did better than medical students or practicing doctors, provided its limitations were observed. Namely, its ontology included bacteria, symptoms, and treatments and did not include patients, doctors, hospitals, death, recovery, and events occurring in time. Its interactions depended on a single patient being considered. Since the experts consulted by the knowledge engineers knew about patients, doctors, death, recovery, etc., it is clear that the knowledge engineers forced what the experts told them into a predetermined framework.

heuristic classification

One of the most feasible kinds of expert system given the present knowledge of AI is to put some information in one of a fixed set of categories using several sources of information.

Forward vs. backward chaining

Forward vs. backward chaining

•FC is data-driven, automatic, unconscious processing,

–e.g., object recognition, routine decisions

•May do lots of work that is irrelevant to the goal

•BC is goal-driven, appropriate for problem-solving,

–e.g., Where are my keys? How do I get into a PhD program?

•Complexity of BC can be much less than linear in size of KB

Inference

Inference: 

•KB ├i α = sentence α can be derived from KB by procedure i

•Soundness: i is sound if whenever KB ├i α, it is also true that KB╞ α

•Completeness: i is complete if whenever KB╞ α, it is also true.

 

•Preview: we will define a logic (first-order logic) which is expressive enough to say almost anything of interest, and for which there exists a sound and complete inference procedure.

•That is, the procedure will answer any question whose answer follows from what is known by the KB.

Logic

Logic:

•Logics are formal languages for representing information such that conclusions can be drawn

•S yntax defines the sentences in the language

•Semantics define the "meaning" of sentences;

 Entailment:

•Entailment means that one thing follows from another:

KB ╞ α

•Knowledge base KB entails sentence α if and only if α is true in all worlds where KB is true

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–E.g., the KB containing “the Giants won” and “the Reds won” entails “Either the Giants won or the Reds won”

–E.g., x+y = 4 entails  4 = x+y

–Entailment is a relationship between sentences (i.e., syntax) that is based on semantics

Artificial Agent

Artificial Agent:

•Representation of knowledge and the reasoning process that brings knowledge to life.

•Knowledge and reasoning -artificial agent.

•Central component of the knowledge-based agent is its knowledge base or KB.

•Knowledge base = set of sentences.

•Language of sentence – Knowledge  representation language.

•Two standard tasks- TELL and ASK.

•Both task , involve – inference (deriving new sentence from old.

 

 

Backtracking search

•Variable assignments are commutative 

            [ WA = red then NT = green ] same as

            [ NT = green then WA = red ]

•Depth-first search for CSPs with single-variable assignments is called backtracking search.

•Chooses values for one variable at a time and backtracks when a variable has no legal value.

•Backtracking search is the basic uninformed algorithm for CSPs