According to the paradigm of Dynamic Logic Programming, knowledge is given by a set of theories (encoded as logic programs) representing different states of the world. Different states may represent time (as in updates), specificity (as in taxonomies), strength of the updating instance (as in the legislative domain), hierarchical position of knowledge source (as in organizations), etc. The mutu...

A semiorder is a model of preference relations where each element x is associated with a utility value α(x), and there is a threshold t such that y is preferred to x iff α(y) > α(x) + t. These are motivated by the notion that there is some uncertainty in the utility values we assign an object or that a subject may be unable to distinguish a preference between objects whose values are close. How...

We show that the problem of coloring a permutation graph of size n can be solved in O(logn logk) time using O(kn2 / logk log2n) processors on the CREW PRAM model of computation, where 1 < k < n. We estimate the parameter k on random permutation graphs and show that the coloring problem can be solved in O(logn loglogn) time in the average-case on the CREW PRAM model of computation with O(n2) pro...

For digraphs D and H, a mapping f : V (D)→V (H) is a homomorphism of D to H if uv ∈ A(D) implies f(u)f(v) ∈ A(H). Let H be a fixed directed or undirected graph. The homomorphism problem for H asks whether a directed or undirected graph input digraph D admits a homomorphism to H. The list homomorphism problem for H is a generalization of the homomorphism problem for H, where every vertex x ∈ V (...

The competition graph of a digraph D is defined as a graph which has the same vertex set as D and has an edge xy between two distinct vertices x and y if and only if, for some vertex z ∈ V (D), the arcs (x, z) and (y, z) are in D. The competition number of a graph G is defined to be the smallest number k such that G together with k isolated vertices is the competition graph of an acyclic digrap...

Graphs appear as simplified representations of a diversity of real-world structures. Naturally there is a question of an intrinsic graph metric, often presumed to be the “shortestpath” metric. Other plausible possibilities for intrinsic graph metrics are formulated in terms of the (combinatorial) Laplacian matrix of the graph, as well as in terms of other combinatoric, probabilistic, and physic...

Bayesian networks, equivalently graphical Markov models determined by acyclic digraphs or ADGs (also called directed acyclic graphs or dags), have proved to be both effective and efficient for representing complex multivariate dependence structures in terms of local relations. However, model search and selection is potentially complicated by the many-to-one correspondence between ADGs and the s...

The issue of characterizing the linear transformations which map certain classes of square matrices into or onto themselves has been the theme of several papers recently written, e.g. [2-4 and 6]. The "into" problem is, in general, harder than the "onto" one, and it has been solved only under some additional hypothesis, namely, nonsingularity of the transformation or a somewhat weaker condition...