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Uncertain Knowledge in AI from Object Automation
- 2. Uncertain Knowledge and Reasoning Abhishek Sharma Object Automation Software Solutions ltd
- 3. Agenda Uncertain Knowledge and Reasoning Causes of uncertainty Probabilistic Reasoning Bayes Rules & use cases Axioms of probability Use case of Bayes Theorem in AI Project – Signature forgery Detection using CNN Siamese network
- 4. Knowledge Representation and Reasoning in AI • Humans are best at understanding, reasoning, and interpreting knowledge. Human knows things, which is knowledge and as per their knowledge they perform various actions in the real world. But how machines do all these things comes under knowledge representation and reasoning. • KR, KRR is the part of AI which concerned with AI agents thinking and how thinking contributes to intelligent behavior of agents. • It is responsible for representing information about the real world so that a computer can understand and can utilize this knowledge to solve the AI problems. • It is also a way which describes how we can represent knowledge in AI. • Knowledge representation is not just storing data into some database, but it also enables an intelligent machine to learn from that knowledge and experiences so that it can behave intelligently like a human.
- 5. knowledge needs to be represented in AI systems • Object: All the facts about objects. E.g., Guitars contains strings, trumpets are brass instruments. • Events: Events are the actions which occur in our world. • Performance: It describe behavior which involves knowledge about how to do things. • Meta-knowledge: It is knowledge about what we know. • Facts: Facts are the truths about the real world and what we represent. Knowledge-Base: The central component of the knowledge-based agents is the knowledge base. It is represented as KB. The Knowledgebase is a group of the Sentences (Here, sentences are used as a technical term and not identical with the English language). Knowledge: Knowledge is awareness or familiarity gained by experiences of facts, data, and situations. Following are the types of knowledge in artificial intelligence
- 6. Issues in knowledge representation • Relationships among attributes : The attributes used to describe objects are nothing but the entities. However, the attributes of an object do not depend on the encoded specific knowledge • Choosing the granularity of representation : While deciding the granularity, it is necessary to know: • i. What are the primitives and at what level should the knowledge be represented? ii. What should be the number (small or large) of low-level primitives or high-level facts? High-level facts may be insufficient to draw the conclusion while Low-level primitives may require a lot of storage. • Representing sets of objects : There are some properties of objects which satisfy the condition of a set together but not as individual; Example: Consider the assertion made in the sentences: "There are more sheep than people in Australia", and "English speakers can be found all over the world." These facts can be described by including an assertion to the sets representing people, sheep, and English • Finding the right structure as needed : To describe a particular situation, it is always important to find the access of right structure. This can be done by selecting an initial structure and then revising the choice
- 7. Uncertainty • If knowledge representation is with certain, means we were sure about the predicates. With this knowledge representation, we might write A→B, which means if A is true then B is true, • But consider a situation where we are not sure about whether A is true or not then we cannot express this statement, this situation is called uncertainty. • So to represent uncertain knowledge, where we are not sure about the predicates, we need uncertain reasoning or probabilistic reasoning. Causes of uncertainty • Information occurred from unreliable sources. • Experimental Errors • Equipment fault • Temperature variation • Climate change.
- 8. Uncertain Knowledge and Reasoning • Uncertain knowledge: When the available knowledge has multiple causes leading to multiple effects or incomplete knowledge of causality in the domain • Uncertain data: Data that is missing, unreliable, inconsistent or noisy • Uncertain knowledge representation: The representations which provides a restricted model of the real system, or has limited expressiveness • Inference: In case of incomplete or default reasoning methods, conclusions drawn might not be completely accurate.
- 9. Uncertainty can be dealt with using • Probability theory • Truth Maintenance systems • Fuzzy logic.
- 10. Probabilistic reasoning • It is a way of knowledge representation where we apply the concept of probability to indicate the uncertainty in knowledge. • We combine probability theory with logic to handle the uncertainty. • We use probability in probabilistic reasoning because it provides a way to handle the uncertainty that is the result of someone's laziness and ignorance. • In the real world, there are lots of scenarios, where the certainty of something is not confirmed, such as "It will rain today," "behavior of someone for some situations," "A match between two teams or two players." • These are probable sentences for which we can assume that it will happen but not sure about it, so here we use probabilistic reasoning.
- 11. Need of probabilistic reasoning in AI • When there are unpredictable outcomes. • When specifications or possibilities of predicates becomes too large to handle. • When an unknown error occurs during an experiment. • In probabilistic reasoning, there are two ways to solve problems with uncertain knowledge: • Bayes' rule • Bayesian Statistics
- 12. Probability • Probability can be defined as a chance that an uncertain event will occur. It is the numerical measure of the likelihood that an event will occur. The value of probability always remains between 0 and 1 that represent ideal uncertainties. • 0 ≤ P(A) ≤ 1, where P(A) is the probability of an event A. • P(A) = 0, indicates total uncertainty in an event A. • P(A) =1, indicates total certainty in an event A.
- 13. Probability • P(¬A) = probability of a not happening event. • P(¬A) + P(A) = 1. • Event: Each possible outcome of a variable is called an event. • Sample space: The collection of all possible events is called sample space. • Random variables: Random variables are used to represent the events and objects in the real world. • Prior probability: The prior probability of an event is probability computed before observing new information. • Posterior Probability: The probability that is calculated after all evidence or information has taken into account. It is a combination of prior probability and new information.
- 14. Axioms of Probability • There are three axioms of probability that make the foundation of probability theory- • Axiom 1: Probability of Event • The first one is that the probability of an event is always between 0 and 1. 1 indicates definite action of any of the outcome of an event and 0 indicates no outcome of the event is possible. • Axiom 2: Probability of Sample Space • For sample space, the probability of the entire sample space is 1. • Axiom 3: Mutually Exclusive Events • And the third one is- the probability of the event containing any possible outcome of two mutually disjoint is the summation of their individual probability.
- 15. Probability of Event • The first axiom of probability is that the probability of any event is between 0 and 1. • As we know the formula of probability is that we divide the total number of outcomes in the event by the total number of outcomes in sample space. • And the event is a subset of sample space, so the event cannot have more outcome than the sample space. • Clearly, this value is going to be between 0 and 1 since the denominator is always greater than the numerator.
- 16. Probability of Sample Space • The second axiom is that the probability for the entire sample space equals 1.
- 17. Mutually Exclusive Event • When there is nothing common between A and B. These particular type of events which is called Mutually Exclusive Events. • These Mutually exclusive events mean that such events cannot occur together or in other words, they don’t have common values or we can say their intersection is zero/null. We can also represent such events as follows:
- 18. Conditional probability • Conditional probability is a probability of occurring an event when another event has already happened. • Let's suppose, we want to calculate the event A when event B has already occurred, "the probability of A under the conditions of B", it can be written as:Where P(A⋀B)= Joint probability of a and B • P(B)= Marginal probability of B. • If the probability of A is given and we need to find the probability of B, then it will be given as:
- 19. Vien Diagram
- 20. Example • In a class, there are 70% of the students who like English and 40% of the students who likes English and mathematics, and then what is the percent of students those who like English also like mathematics? • Let, A is an event that a student likes Mathematics • B is an event that a student likes English. • Hence, 57% are the students who like English also like Mathematics.
- 21. Bayes' theorem in Artificial intelligence .
- 22. Bayes' theorem • Bayes' theorem is also known as Bayes' rule, Bayes' law, or Bayesian reasoning, which determines the probability of an event with uncertain knowledge. • In probability theory, it relates the conditional probability and marginal probabilities of two random events. • Bayes' theorem was named after the British mathematician Thomas Bayes. The Bayesian inference is an application of Bayes' theorem, which is fundamental to Bayesian statistics. • It is a way to calculate the value of P(B|A) with the knowledge of P(A|B). • Bayes' theorem allows updating the probability prediction of an event by observing new information of the real world.
- 23. Example • If cancer corresponds to one's age then by using Bayes' theorem, we can determine the probability of cancer more accurately with the help of age. • Bayes' theorem can be derived using product rule and conditional probability of event A with known event B: • As from product rule we can write: • P(A ⋀ B)= P(A|B) P(B) or • Similarly, the probability of event B with known event A: • P(A ⋀ B)= P(B|A) P(A) • Equating right hand side of both the equations, we will get:
- 24. Example • The above equation (a) is called as Bayes' rule or Bayes' theorem. This equation is basic of most modern AI systems for probabilistic inference. • It shows the simple relationship between joint and conditional probabilities. Here, • P(A|B) is known as posterior, which we need to calculate, and it will be read as Probability of hypothesis A when we have occurred an evidence B. • P(B|A) is called the likelihood, in which we consider that hypothesis is true, then we calculate the probability of evidence. • P(A) is called the prior probability, probability of hypothesis before considering the evidence • P(B) is called marginal probability, pure probability of an evidence. • In the equation (a), in general, we can write P (B) = P(A)*P(B|Ai), hence the Bayes' rule can be written as: • Where A1 , A2 , A3 ,........, An is a set of mutually exclusive and exhaustive events.
- 25. Applying Bayes' rule • Bayes' rule allows us to compute the single term P(B|A) in terms of P(A|B), P(B), and P(A). • This is very useful in cases where we have a good probability of these three terms and want to determine the fourth one. • Suppose we want to perceive the effect of some unknown cause, and want to compute that cause, then the Bayes' rule becomes:
- 26. Example-1 • A doctor is aware that disease meningitis causes a patient to have a stiff neck, and it occurs 80% of the time. He is also aware of some more facts, which are given as follows: • The Known probability that a patient has meningitis disease is 1/30,000. • The Known probability that a patient has a stiff neck is 2%. • Let a be the proposition that patient has stiff neck and b be the proposition that patient has meningitis. , so we can calculate the following as: • P(a|b) = 0.8 • P(b) = 1/30000 • P(a)= .02 • Hence, we can assume that 1 patient out of 750 patients has meningitis disease with a stiff neck.
- 27. Question From a standard deck of playing cards, a single card is drawn. The probability that the card is king is 4/52, then calculate posterior probability P(King|Face), which means the drawn face card is a king card.4 • P(king): probability that the card is King= 4/52= 1/13 • P(face): probability that a card is a face card= 3/13 • P(Face|King): probability of face card when we assume it is a king = 1 • Putting all values in equation (i) we will get:
- 28. Application of Bayes' theorem in Artificial intelligence • Bayes Theorem is also widely used in the field of machine learning and AI • Including its use in a probability framework for fitting a model to a training dataset, referred to as maximum a posteriori or MAP for short, and in developing models for classification predictive modeling problems such as the Bayes Optimal Classifier and Naive Bayes. • It is used to calculate the next step of the robot when the already executed step is given. • Bayes' theorem is helpful in weather forecasting. • It can solve the Monty Hall problem.