Showing papers in "Acta Informatica in 1971"
TL;DR: A “director-secretary” relationship will be introduced to reflect a possible discipline in the use of sequencing primitives and an analysis of the requirements of the correctness proofs will give an insight into the logical issues at hand.
Abstract: One of the primary functions of an operating system is to rebuild a machine that must be regarded as non-deterministic (on account of cycle stealing and interrupts) into a more or less deterministic automaton. Taming the degree of indeterminacy in steps will lead to a layered operating system. A bottom layer will be discussed and so will the adequacy of the interface it presents. An analysis of the requirements of the correctness proofs will give us an insight into the logical issues at hand. A "director-secretary" relationship will be introduced to reflect a possible discipline in the use of sequencing primitives.
797 citations
TL;DR: Pascal was developed on the basis of Algol 60 with emphasis placed on keeping the number of fundamental concepts reasonably small, on a simple and systematic language structure, and on efficient implementability.
Abstract: A programming language called Pascal is described which was developed on the basis ofAlgol 60. Compared toAlgol 60, its range of applicability is considerably increased due to a variety of data structuring facilities. In view of its intended usage both as a convenient basis to teach programming and as an efficient tool to write large programs, emphasis was placed on keeping the number of fundamental concepts reasonably small, on a simple and systematic language structure, and on efficient implementability. A one-pass compiler has been constructed for the CDC 6000 computer family; it is expressed entirely in terms of Pascal itself.
561 citations
398 citations
TL;DR: A method for the computation of the greatest common divisor of two integers u, v and of the continued fraction for u/v is modified in such a way that only O(n(lg n)2(lglg n)) elementary steps are used for u,v<.2n.
Abstract: A method, given by D. E. Knuth for the computation of the greatest common divisor of two integers u, v and of the continued fraction for u/v is modified in such a way that only O(n(lg n)2(lglg n)) elementary steps are used for u,v<.2 n.
Ein von D. E. Knuth angegebenes Verfahren, fur ganze Zahlen u, v den groβten gemeinsamen Teiler und den Kettenbruch fur u/v zu berechnen, wird so modifiziert, daβ fur n-stellige Zahlen nur O(n(lg n)2 (lglg n)) elementare Schritte gebraucht werden.
197 citations
TL;DR: The theory and practice of classical “top-down” parsing methods is presented in a tutorial manner and the results are compared to real-time parsing techniques.
Abstract: The theory and practice of classical "top-down" parsing methods is presented in a tutorial manner.
110 citations
TL;DR: A formal model for automatic error-correction that considers clusters of errors, using a local context to determine the corrections, can be embedded in left-to-right recognizers.
Abstract: A formal model for automatic error-correction is presented. It considers clusters of errors, using a local context to determine the corrections. The process can be embedded in left-to-right recognizers. The recognizer is used for standard syntax checking. When an error is detected, an error correction mechanism is activated which, by a limited backward then forward move, determines the possible corrections. An important aspect of this process is that it does not slow down the parsing of correct programs.
64 citations
TL;DR: An algorithm s to solve the (m, n) problem, which is to determine the linear ordering of their union by means of a sequence of pairwise comparisons between an element of Am and an elements of B~, is said to be M-optimal.
Abstract: The problem is to determine the linear ordering of their union (i.e., to merge A m and B~) by means of a sequence of pairwise comparisons between an element of Am and an element of B~. Given any algorithm s to solve this problem, which we refer to as the (m, n) problem, let K s (m, n) denote the maximum number of comparisons required and E s (m, n) the expected number of comparisons required to merge Am and B~ using s, assuming that all possible initial orderings of A m w B~ are equally likely. An algorithm s is said to be M-optimal if K s (m, n) = K (m, n), where K (m, n) = min K x (m, n), and E-optimal if E s (m, n) = E (m, n), where E (m, n) = miu E,(m, ~).
51 citations
TL;DR: In this paper, the problem of obtaining predictions of the extent to which additional core storage would improve the performance of a given paging system based on information that could be obtained from monitoring the system whilst running its normal workload was addressed.
Abstract: This paper concerns the problem of obtaining predictions of the extent to which additional core storage would improve the performance of a given paging system based on information that could be obtained from monitoring the system whilst running its normal workload.
It is shown that for a large class of replacement algorithms there are efficient techniques for producing exact predictions of the performance improvement, and that for a further class of algorithms statistical predictions can be provided.
48 citations
TL;DR: A constructive model for data structures description based on the concept of data space defined as the Cartesian product of a name space and a value space that is used for classification of data structures into regular, semiregular and irregular data structures.
Abstract: This paper presents a constructive model for data structures description based on the concept of data space defined as the Cartesian product of a name space and a value space. The subsets of name space are ordered by an a priori given selector function. The model is used for classification of data structures into regular (array-like), semiregular (key-ordered list-like) and irregular (threaded list-like) data structures. The notion of data storage structures induced by addressing mechanism is introduced and storage mapping functions are described using this concept together with the data structure model. The first part of the paper contains also some of the model applications to regular and semiregular data structure problems and a brief comparison withAlgol 68 treatment of regular data structures.
12 citations
TL;DR: A simple proof of the decidability of the class L R (k) grammars is given by the help of k-pushdown classes which are introduced in this paper and on a result of Btichi on regular canonical systems.
Abstract: In [2] Knu th consideres a special class of context free grammars (~ which he calls translatable from left to right with bound k>--O (~ E L R (k)). Knuth shows tha t for fixed bound k it can be decided in a finite number of steps whether a context free g rammar is an L R (k) grammar. Here we shall give a different simple proof of the decidability of the class L R (k). The proof is based on a characterization of L R (k) grammars by the help of k-pushdown classes which we introduce in this paper and on a result of Btichi on regular canonical systems [1 ~. A regular canonical system • over a finite a lphabet ~ is a special canonical sys tem with a finite number of product ions of the form ~a = ~b,a, b E~*. ~ is a variable over ~* and indicates tha t replacements m a y be done only at the right end of a word: u is directly derivable from v (v / u) : M v ---xa and u = x b where a = ~ b is a product ion of 27. The transit ive closure I x of ~ in ~* defines the relat ion of general derivability. Biichi shows: If u and v are words in ~* then the genera ted set of words. ~(u,27,v) : =(x~.q*:u ~xv}
10 citations
TL;DR: Formal transformations of programs or switching circuits can be described by a system of relations within the concept of free X-categories, which can be applied only to loopfree switching circuits or programs, but loops may easily be presented in afree X-category.
Abstract: Formal transformations of programs or switching circuits can be described by a system of relations within the concept of free X-categories. In this theory the programs or switching circuits are the morphisms of the free X-category. A finite relation system is given which is correct and complete (in an analogous sense to the notions of the predicate calculus) and which describes the transformations of programs or switching circuits. At first this system can be applied only to loopfree switching circuits or programs, but loops may easily be presented in a free X-category. All these subjects will thoroughly be discussed in this paper.
TL;DR: There exists an automaton whose automorphism group is isomorphic to G and such that the quotient by the automorphist congruence is $$\mathfrak{A}$$ .
Abstract: We study a class of congruences of strongly connected finite automata, called the group congruences, which may be defined in this way: every element fixing any class of the congruence induces a permutation on this class. These congruences form an ideal of the lattice of all congruences of the automaton $$\mathfrak{A}$$ and we study the group associated with the maximal group congruence (maximal induced group) with respect to the Suschkevitch group of the transition monoid of $$\mathfrak{A}$$ . The transitivity equivalence of the subgroups of the automorphism group of $$\mathfrak{A}$$ are found to be the group congruences associated with regular groups, which form also in ideal of the lattice of congruences of $$\mathfrak{A}$$ . We then characterize the automorphism group of $$\mathfrak{A}$$ with respect to the maximal induced group. As an application, we show that, given a group G and an automaton $$\mathfrak{A}$$ , there exists an automaton whose automorphism group is isomorphic to G and such that the quotient by the automorphism congruence is $$\mathfrak{A}$$ .