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Harmful Internet hijacking incidents put in evidence how fragile interdomain routing is. In particular, the Border Gateway Protocol (BGP), which is used to exchange routing information between Internet entities, called Autonomous Systems (ASes), proved to be prone to attacks launched by a single malicious AS. Recent research contributions pointed out that even S-BGP, the secure variant of BGP that is being deployed, is not fully able to blunt traffic attraction attacks. Given a traffic flow between two ASes, we study how difficult it is for a malicious AS to devise a strategy for hijacking or intercepting that flow. The goal of the attack is to attract a traffic flow towards the malicious AS. While in the hijacking attack connectivity between the endpoints of a flow can be disrupted, in the interception attack connectivity must be maintained. We show that this problem marks a sharp difference between BGP and S-BGP. Namely, while it is solvable, under reasonable assumptions, in polynomial time for the type of attacks that are usually performed in BGP, it is NP-hard for S-BGP. Our study has several by-products. E.g., we solve a problem left open in the literature, stating when performing a hijacking in S-BGP is equivalent to performing an interception. [ABSTRACT FROM AUTHOR]

Abstract: Consider a planar drawing of a planar graph such that the vertices are drawn as small circles and the edges are drawn as thin stripes. Consider a non-simple cycle of . Is it possible to draw as a non-intersecting closed curve inside , following the circles that correspond in to the vertices of and the stripes that connect them? We show that this test can be done in polynomial time and study this problem in the framework of clustered planarity for highly non-connected clustered graphs. [Copyright &y& Elsevier]

A diagram is a drawing on the plane that represents a graph-like structure, where nodes are represented by symbols and edges are represented by curves connecting pairs of symbols. An automatic layout facility is a tool that receives as input a graph-like structure and is able to produce a diagram that nicely represents such a structure. Many systems use diagrams in the interaction with the users; thus, automatic layout facilities and algorithms for graphs layout have been extensively studied in the last years. We present a new approach in designing an automatic layout facility. Our approach is based on a modular management of a large collection of algorithms and on a strategy that, given the requirements of an application, selects a suitable algorithm for such requirements. The proposed approach has been used for designing the automatic layout facility of Diagram Server, a network server that offers to its clients several facilities for managing diagrams. [ABSTRACT FROM AUTHOR]

The data dictionary contains the description of all types of data produced, managed, exchanged, and maintained in an organization. Data descriptions (very often hundreds of schemas) should be organized in such a way to allow all the users of the information system to understand the meaning of data and their relationships. In this paper, a new set of structuring primitives is presented for a dictionary of entity relationship data schemas. The formal properties of such structuring primitives ire investigated and the feasibility of their usage is shown by providing a methodology for dictionary design. [ABSTRACT FROM AUTHOR]

In this paper we settle the computational complexity of two open problems related to the extension of the notion of level planarity to surfaces different from the plane. Namely, we show that the problems of testing the existence of a level embedding of a level graph on the surface of the rolling cylinder or on the surface of the torus, respectively known by the name of Cyclic Level Planarity and Torus Level Planarity , are polynomial-time solvable. Moreover, we show a complexity dichotomy for testing the Simultaneous Level Planarity of a set of level graphs, with respect to both the number of level graphs and the number of levels. [ABSTRACT FROM AUTHOR]

In a drawing of a clustered graph vertices and edges are drawn as points and curves, respectively, while clusters are represented by simple closed regions. A drawing of a clustered graph is c-planar if it has no edge–edge, edge–region, or region–region crossings. Determining the complexity of testing whether a clustered graph admits a c-planar drawing is a long-standing open problem in the Graph Drawing research area. An obvious necessary condition for c-planarity is the planarity of the graph underlying the clustered graph. However, this condition is not sufficient and the consequences on the problem due to the requirement of not having edge–region and region–region crossings are not yet fully understood. In order to shed light on the c-planarity problem, we consider a relaxed version of it, where some kinds of crossings (either edge–edge, edge–region, or region–region) are allowed even if the underlying graph is planar. We investigate the relationships among the minimum number of edge–edge, edge–region, and region–region crossings for drawings of the same clustered graph. Also, we consider drawings in which only crossings of one kind are admitted. In this setting, we prove that drawings with only edge–edge or with only edge–region crossings always exist, while drawings with only region–region crossings may not. Further, we provide upper and lower bounds for the number of such crossings. Finally, we give a polynomial-time algorithm to test whether a drawing with only region–region crossings exists for biconnected graphs, hence identifying a first non-trivial necessary condition for c-planarity that can be tested in polynomial time for a noticeable class of graphs. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we analyze the relationships among different planar embeddings of the same graph and study how two planar embeddings can be morphed one into the other with the minimum number of elementary changes, while preserving the mental map of the user. We call this problem Topological Morphing, in analogy with the well-known Geometric Morphing problem, in which it is studied how two planar drawings can be morphed one into the other with the minimum number of elementary changes. First, we define two operations, called flip and skip, describing natural transformations of a graph embedding that preserve the mental map of the user. Then, we study the problem of performing a morph while minimizing the number of these operations. We show that the Topological Morphing problem is NP-hard for biconnected planar graphs, we give polynomial-time algorithms for some restricted versions of the problem, and, based on such polynomial-time algorithms, we give a fixed-parameter tractable algorithm for the general case. [Copyright &y& Elsevier]

A simple topological graph is k -quasiplanar (k ≥ 2) if it contains no k pairwise crossing edges, and k -planar if no edge is crossed more than k times. In this paper, we explore the relationship between k -planarity and k -quasiplanarity to show that, for k ≥ 2 , every k -planar simple topological graph can be transformed into a (k + 1) -quasiplanar simple topological graph. [ABSTRACT FROM AUTHOR]