Krishnamurthy, R., Ramakrishnan, R., and Shmueli, O. A framework for testing safety and e#ective computability. Journal of Computer and System Sciences 52 (1996), 100--124.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....x is a substring of y. If only y is given then occurs(x,y) produces as outputs x all substrings of y. This is again analogous to logic programming [12] where free variables are bound into result values. The ability to generate output extends the safety aspect common to database query evaluation [11] because it is now possible to formulate queries with infinite answer sets already in the level of the string programs in addition to the query language level. For example, given only x as input occurs(x,y) would match infinitely many y and should therefore be rejected from evaluation. Thus for ....

Krishnamurthy, R., Ramakrishnan, R., and Shmueli, O. A framework for testing safety and e#ective computability. Journal of Computer and System Sciences 52 (1996), 100--124.

....the general case. The more stringent condition given above is enforced by repeatedly deleting those transitions, which can justifiably be argued not to take part in any loops of the kind mentioned in Observation 2. This technique is related to analyzing the input output behavior of logic programs [16,26], which analyze the call graph of the given program component by component. However, our technique remains simpler, because our automata are more restricted than general logic programs. 9 function halting( G :transition graph GA of a k FSA A; X:subset of 1, k ) B; 1: b # 1; 2: ....

Krishnamurthy, R., Ramakrishnan, R., and Shmueli, O. A framework for testing safety and e#ective computability. Journal of Computer and System Sciences 52 (1996), 100--124.

....on the value, which is the given value of K. Thus it can be concluded that the number of iterations is finite and each iteration produces only finite tuples. Consequently, the rule is safe. In general, the problem of checking for safety is undecidable. The safety checking algorithm proposed in [KrRS] is to find a well founded formula that can be used as a su#cient condition to guarantee safety. This algorithm is an enumerative algorithm that exhausts an exponential number of cases, to ensure the existence of a well founded formula for each recursive cycle. The enumerative algorithm guesses ....

Krishnamurthy, R. R. Ramakrishnan and O. Shmueli, "A Framework for Testing Safety and E#ective Computability," Proc. ACM SIGMOD Int. Conf. on Management of Data, pp. 154--163, 1988.

....Datalog E Programs We now introduce a class of Datalog E programs. Our goal is to identify the programs that can be executed without generating infinite relations for external predicates and that can be compiled separately. First, we recall the notion of finiteness constraint (FC) from [KRS88]. Intuitively, this captures the notion of the input output requirements of an external predicate. A computed predicate p is said to satisfy a finiteness constraint of the form X # Y if and only if for each tuple T in p, the set of tuples S[Y ] S # p and S[X] T [X] is finite. 2 ....

....global predicates, since it can be inferred during compilation. Briefly, the input bindings are specified in the query form for which the program is compiled. During compilation, safety analysis guarantees that the resulting execution will produce a finite result when applied to a finite database[KRS88]. In other words, if the arguments x 1 , x 2 , x k are used for input and y 1 , y 2 , y m are 2 Note this notion is strictly weaker than that of functional dependency. 3 the output arguments specified, the compiler guarantees the FC x 1 , x 2 , x k # y 1 , y 2 , ....

Krishnamurthy, R., R. Ramakrishnan, O. Shmueli. "Framework for Testing Safety and E#ective Computability of Extended Datalog," in SIGMOD, Chicago, 1988.

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