Each level of the tree is called a ply. Since the same state may be reachable by different sequences of moves, the state space may in general be a graph. It may be treated as a tree for simplicity, at the cost of duplicating states. 81 Solving problems using search Given an informal description of the problem, construct a formal description as a state space: Define a data structure to represent the state a principal type scheme? Give the principal type scheme for N1, or explain informally why it does not have one. On average, how many such questions will need to be asked before the symbol is discovered? What is the entropy of the symbol set? [2 marks] Construct a uniquely decodable prefix code for the symbols. Explain why it is uniquely decodable and why it has the prefix property. [2 marks] 10 CST.2017.8.9 11 Security I (a) Windows implements static inheritance for the access-control lists of NTFS files and folders. (i) What does static inheritance mean here and how does it differ from dynamic inheritance? [4 marks] (ii) Five flag bits (ci,oi,np,io,i) in each NTFS access-control entry (ACE) manage how it is inherited. Briefly describe the purpose of each bit. y If it already exists, then a. Set the node that is being expanded to the point to the already existing node corresponding to its successor rather than to the new one. The new one can be thrown away. 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. For example, when given the tree shown above as the first argument the predicate should unify the second argument with the list [4,2,7,4,2,6]. [4 marks] When creating a network application, the developer's main task is therefore to write the code for both the client and server programs. There are two types of network applications. One type is an implementation whose operation is specified in a protocol standard, such as an RFC or some other standards document; such an application is sometimes referred to as "open," since the rules specifying its operation are known to all. Relate the bits in the code words forming your prefix code to the 'yes/no' questions that you proposed in (a). [3 marks] (b) Explain how the bits in an IrisCode are set by phase sequencing. Discuss how quantisation of the complex plane into phase quadrants sets each pair of bits; why it is beneficial for quadrant codes to form a Gray Code; how much entropy is thereby typically extracted from iris images; and why such bit sequences enable extremely efficient identity searches and matching. [4 marks] (i) Explain why the bfs/2 predicate might benefit from being converted to use difference lists. [2 marks] (ii) Implement a new predicate diffbfs/2 which makes use of a difference list to exploit the benefit you identified in part (iii).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, i.e. constitutes an advance toward the goal, may be more useful. 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. To illustrate how their modes of operation work, we can use instead a pseudo-random permutation that operates on the 26 letters of the English alphabet: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 m A B C D E F G H I J K L M N O P Q R S T U V W X Y Z EK(m) P K X C Y W R S E J U D G O Z A T N M V F H L I B Q As the XOR operation is not defined on the set {A, . . . , Z}, we replace it here during encryption with modulo-62 addition (e.g., C D = F and Y C = A). Some prominent intelligent search algorithms are stated below: 1. Generate and Test Search 2. Best-first Search 3. Greedy Search 4. A* Search 5. Constraint Search 6. Means-ends analysis There are some more algorithms. They are either improvements or combinations of these. If the best or shortest path is being determined, check to see if this path is better or worse than the old one. If worse, do nothing. Search Tree The sequence of states formed by possible moves is called a search tree.