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30
An Incremental Algorithm for a Generalization of the ShortestPath Problem
, 1992
"... The grammar problem, a generalization of the singlesource shortestpath problem introduced by Knuth, is to compute the minimumcost derivation of a terminal string from each nonterminal of a given contextfree grammar, with the cost of a derivation being suitably defined. This problem also subsume ..."
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Cited by 139 (1 self)
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The grammar problem, a generalization of the singlesource shortestpath problem introduced by Knuth, is to compute the minimumcost derivation of a terminal string from each nonterminal of a given contextfree grammar, with the cost of a derivation being suitably defined. This problem also subsumes the problem of finding optimal hyperpaths in directed hypergraphs (under varying optimization criteria) that has received attention recently. In this paper we present an incremental algorithm for a version of the grammar problem. As a special case of this algorithm we obtain an efficient incremental algorithm for the singlesource shortestpath problem with positive edge lengths. The aspect of our work that distinguishes it from other work on the dynamic shortestpath problem is its ability to handle "multiple heterogeneous modifications": between updates, the input graph is allowed to be restructured by an arbitrary mixture of edge insertions, edge deletions, and edgelength changes.
Finding the k shortest hyperpaths
"... The K shortest paths problem has been extensively studied for many years. Efficient methods have been devised, and many practical applications are known. Shortest hyperpath models have been proposed for several problems in different areas, for example in relation with routing in dynamic networks. Ho ..."
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Cited by 19 (3 self)
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The K shortest paths problem has been extensively studied for many years. Efficient methods have been devised, and many practical applications are known. Shortest hyperpath models have been proposed for several problems in different areas, for example in relation with routing in dynamic networks. However, the K shortest hyperpaths problem has not yet been investigated. In this paper we present procedures for finding the K shortest hyperpaths in a directed hypergraph. This is done by extending existing algorithms for K shortest loopless paths. Computational experiments on the proposed procedures are performed, and applications in transportation, planning and combinatorial optimization are discussed.
Hierarchical Hippocratic Databases with Minimal Disclosure for Virtual Organizations
 VLDBJ
"... Abstract The protection of customer privacy is a fundamental issue in today’s corporate marketing strategies. Not surprisingly, many research efforts have proposed new privacyaware technologies. Among them, Hippocratic databases offer mechanisms for enforcing privacy rules in database systems for i ..."
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Cited by 17 (6 self)
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Abstract The protection of customer privacy is a fundamental issue in today’s corporate marketing strategies. Not surprisingly, many research efforts have proposed new privacyaware technologies. Among them, Hippocratic databases offer mechanisms for enforcing privacy rules in database systems for interorganizational business processes (also known as virtual organizations). This paper extends these mechanisms to allow for hierarchical purposes, distributed authorizations and minimal disclosure supporting the business processes of virtual organizations that want to offer their clients a number of ways to fulfill a service. Specifically, we use a goaloriented approach to analyze privacy policies of the enterprises involved in a business process. Based on the purpose hierarchy derived through a goal refinement process, we provide algorithms for determining the minimum set of authorizations needed to achieve a service. This allows us to automatically derive access control policies for an interorganizational business process from the collection of privacy policies associated with different participating enterprises. By using effective online algorithms, the derivation of such minimal information can also be done onthefly by the customer wishing to access a service.
The maxatom problem and its relevance
 In Proc. of Int. Conf. on Logic for Programming, Artificial Intelligence and Reasoning (LPAR
, 2008
"... Abstract. Let F be a conjunction of atoms of the form max(x, y)+k ≥ z, where x, y, z are variables and k is a constant value. Here we consider the satisfiability problem of such formulas (e.g., over the integers or rationals). This problem, which appears in unexpected forms in many applications, is ..."
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Cited by 9 (0 self)
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Abstract. Let F be a conjunction of atoms of the form max(x, y)+k ≥ z, where x, y, z are variables and k is a constant value. Here we consider the satisfiability problem of such formulas (e.g., over the integers or rationals). This problem, which appears in unexpected forms in many applications, is easily shown to be in NP. However, decades of efforts (in several research communities, see below) have not produced any polynomial decision procedure nor an NPhardness result for thisapparently so simple problem. Here we develop several ingredients (smallmodel property and lattice structure of the model class, a polynomially tractable subclass and an inference system) which altogether allow us to prove the existence of small unsatisfiability certificates, and hence membership in NP intersection coNP. As a byproduct, we also obtain a weakly polynomial decision procedure. We show that the Maxatom problem is PTIMEequivalent to several other wellknownand at first sight unrelated problems on hypergraphs and on Discrete Event Systems, problems for which the existence of PTIME algorithms is also open. Since there are few interesting problems in NP intersection coNP that are not known to be polynomial, the Maxatom problem appears to be relevant.
A structure for modern computer narratives
 In CG’2002: International Conference on Computers and Games, volume 2883 of LNCS
, 2002
"... Abstract. In order to analyze or better develop modern computer games it is critical to have an appropriate representation framework. In this paper a symbolic representation of modern computer narratives is described, and related to a general model of operational behaviour. The resulting structure c ..."
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Cited by 7 (3 self)
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Abstract. In order to analyze or better develop modern computer games it is critical to have an appropriate representation framework. In this paper a symbolic representation of modern computer narratives is described, and related to a general model of operational behaviour. The resulting structure can then be used to verify desirable properties, or as the basis for a narrative development system. 1
Mode directed path finding
 In Lecture notes in computer science: Vol. 3720. Proceedings of the 16th European Conference on Machine Learning
, 2005
"... Abstract. Learning from multirelational domains has gained increasing attention over the past few years. Inductive logic programming (ILP) systems, which often rely on hillclimbing heuristics in learning firstorder concepts, have been a dominating force in the area of multirelational concept lea ..."
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Cited by 7 (1 self)
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Abstract. Learning from multirelational domains has gained increasing attention over the past few years. Inductive logic programming (ILP) systems, which often rely on hillclimbing heuristics in learning firstorder concepts, have been a dominating force in the area of multirelational concept learning. However, hillclimbing heuristics are susceptible to local maxima and plateaus. In this paper, we show how we can exploit the links between objects in multirelational data to help a firstorder rule learning system direct the search by explicitly traversing these links to find paths between variables of interest. Our contributions are twofold: (i) we extend the pathfinding algorithm by Richards and Mooney [12] to make use of mode declarations, which specify the mode of call (input or output) for predicate variables, and (ii) we apply our extended path finding algorithm to saturated bottom clauses, which anchor one end of the search space, allowing us to make use of background knowledge used to build the saturated clause to further direct search. Experimental results on a mediumsized dataset show that path finding allows one to consider interesting clauses that would not easily be found by Aleph. 1
Hypergraph Traversal Revisited: Cost Measures and Dynamic Algorithms
 LECTURE NOTES IN COMPUTER SCIENCE
, 1998
"... Directed hypergraphs are used in several applications to model different combinatorial structures. A directed hypergraph is defined by a set of nodes and a set of hyperarcs, each connecting a set of source nodes to a single target node. A hyperpath, similarly to the notion of path in directed g ..."
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Cited by 6 (0 self)
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Directed hypergraphs are used in several applications to model different combinatorial structures. A directed hypergraph is defined by a set of nodes and a set of hyperarcs, each connecting a set of source nodes to a single target node. A hyperpath, similarly to the notion of path in directed graphs, consists of a connection among nodes using hyperarcs. Unlike paths in graphs, however, hyperpaths are suitable of many different definitions of measure, corresponding to different concepts arising in various applications. In this paper we consider the problem of finding optimal hyperpaths according to several measures. We also provide results that may shed some light on the intrinsic complexity of finding optimal hyperpaths.
Trees of Shortest Paths vs. Steiner Trees: Understanding and Improving Delete Relaxation Heuristics
"... Heuristic search using heuristics extracted from the delete relaxation is one of the most effective methods in planning. Since finding the optimal solution of the delete relaxation is intractable, various heuristics introduce independence assumptions, the implications of which are not yet fully unde ..."
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Cited by 6 (0 self)
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Heuristic search using heuristics extracted from the delete relaxation is one of the most effective methods in planning. Since finding the optimal solution of the delete relaxation is intractable, various heuristics introduce independence assumptions, the implications of which are not yet fully understood. Here we use concepts from graph theory to show that in problems with unary action preconditions, the delete relaxation is closely related to the Steiner Tree problem, and that the independence assumption for the set of goals results in a treeofshortestpaths approximation. We analyze the limitations of this approximation and develop an alternative method for computing relaxed plans that addresses them. The method is used to guide a greedy bestfirst search, where it is shown to improve plan quality and coverage over several benchmark domains. 1
Linear Connectivity Problems in Directed Hypergraphs
"... We introduce a notion of hyperconnection (formally denoted Lhyperpath) between nodes in a directed hypergraph and relate this notion to existing notions of hyperpaths in directed hypergraphs. We show that some interesting questions in problem domains such as secret transfer protocols and routing in ..."
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Cited by 5 (0 self)
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We introduce a notion of hyperconnection (formally denoted Lhyperpath) between nodes in a directed hypergraph and relate this notion to existing notions of hyperpaths in directed hypergraphs. We show that some interesting questions in problem domains such as secret transfer protocols and routing in packet filtered networks are basically questions about the existence of Lhyperpaths in directed hypergraphs. We study the computational complexity of problems related to Lhyperpaths and the Lcyclomatic number of directed hypergraphs (the minimum number of hyperedges that need to be deleted to make a directed hypergraph free of Lhypercycles). We prove that the Lhyperpath existence problem, the Lcyclomatic number problem, the minimum Lcyclomatic set problem, and the minimal Lcyclomatic, Πp, and DP, respectively. set problem are each complete for the complexity class NP, Σ p 2 1
Modelling of quality of protection in outsourced business processes
 In Proc. of IAS’07. IEEE
"... There is a large number of research papers and standards dedicated to security for outsourced data. Yet, most papers propose new controls to access and protect the data rather than to assess the level of assurance of the whole process that is currently deployed. The main contributions of the paper ..."
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Cited by 5 (2 self)
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There is a large number of research papers and standards dedicated to security for outsourced data. Yet, most papers propose new controls to access and protect the data rather than to assess the level of assurance of the whole process that is currently deployed. The main contributions of the paper is an approach for aggregating security properties of individual tasks of a complex business process in order to receive the level of assurance provided by the whole process. The approach takes into account the fact that some tasks of a business process may be outsourced and thus account for not very reliable partners. The approach chooses the concrete business process offering the highest assurance among several possible design alternatives by building an optimal hyperpath traversing the business process. 1