Mohammed Amin Tahraoui

Component-cardinality-constrained critical node problem in graphs

An effective way to analyze and apprehend the structural properties of networks is to find their most critical nodes. This makes them easier to control, whether the purpose is to keep or to delete them. Given a graph, Critical Node Detection problem (CNDP) consists in finding a set of nodes, deletion of which satisfies some given connectivity metrics in the induced graph. In this paper, we propose and study a new variant of this problem, called Component-Cardinality-Constrained Critical Node Problem (3C-CNP). In this variant, we seek to find a minimal set of nodes, removal of which constrains the size of each connected component in the induced graph to a given bound. We prove the NP-hardness of this problem on a graph of maximum degree Δ = 4 , through which we deduce the NP-hardness of CNP (Arulselvan etźal., 2009) on the same class of graphs. Also, we study 3C-CNP on trees for different cases depending on node weights and connection costs. For the case where node weights and connection costs have non-negative values, we prove its NP-completeness. While, for the case where node weights (or connection costs) have unit values, we present a polynomial algorithm. Also, we study 3C-CNP on chordal graphs, where we show that it is NP-complete on split graphs, and polynomially solvable on proper interval graphs.

Gap vertex-distinguishing edge colorings of graphs

Abstract In this paper, we study a new coloring parameter of graphs called the gap vertex-distinguishing edge coloring . It consists in an edge-coloring of a graph G which induces a vertex distinguishing labeling of G such that the label of each vertex is given by the difference between the highest and the lowest colors of its adjacent edges. The minimum number of colors required for a gap vertex-distinguishing edge coloring of G is called the gap chromatic number of G and is denoted by gap ( G ) . We here study the gap chromatic number for a large set of graphs G of order n and prove that gap ( G ) ∈ { n − 1 , n , n + 1 } .

A survey on tree matching and XML retrieval

With the increasing number of available XML documents, numerous approaches for retrieval have been proposed in the literature. They usually use the tree representation of documents and queries to process them, whether in an implicit or explicit way. Although retrieving XML documents can be considered as a tree matching problem between the query tree and the document trees, only a few approaches take advantage of the algorithms and methods proposed by the graph theory. In this paper, we aim at studying the theoretical approaches proposed in the literature for tree matching and at seeing how these approaches have been adapted to XML querying and retrieval, from both an exact and an approximate matching perspective. This study will allow us to highlight theoretical aspects of graph theory that have not been yet explored in XML retrieval.

The Critical Node Detection Problem in networks: A survey

Abstract In networks, not all nodes have the same importance, and some are more important than others. The issue of finding the most important nodes in networks has been addressed extensively, particularly for nodes whose importance is related to network connectivity. These nodes are usually known as Critical Nodes. The Critical Node Detection Problem (CNDP) is the optimization problem that consists in finding the set of nodes, the deletion of which maximally degrades network connectivity according to some predefined connectivity metrics. Recently, this problem has attracted much attention, and depending on the predefined metric, different variants have been developed. In this survey, we review, classify and discuss several recent advances and results obtained for each variant, including theoretical complexity, exact solving algorithms, approximation schemes and heuristic approaches. We also prove new complexity results and induce some solving algorithms through relationships established between different variants.

Labeled embedding of (n, n − 2)-graphs in their complements

Abstract Graph packing generally deals with unlabeled graphs. In [4], the authors have introduced a new variant of the graph packing problem, called the labeled packing of a graph. This problem has recently been studied on trees [M.A. Tahraoui, E. Duchêne and H. Kheddouci, Labeled 2-packings of trees, Discrete Math. 338 (2015) 816-824] and cycles [E. Duchˆene, H. Kheddouci, R.J. Nowakowski and M.A. Tahraoui, Labeled packing of graphs, Australas. J. Combin. 57 (2013) 109-126]. In this note, we present a lower bound on the labeled packing number of any (n, n − 2)-graph into Kn. This result improves the bound given by Woźniak in [Embedding graphs of small size, Discrete Appl. Math. 51 (1994) 233-241].

Labeled 2-packings of trees

Graph packing generally deals with unlabeled graphs. In Duchene et?al. (2013), the authors introduced a new variant of the graph packing problem, called labeled packing of a graph. In the current paper, we present several results about the labeled packing number of trees. Exact values are given in the cases of paths and caterpillars. For a general tree, a lower bound is given thanks to the introduction of the concept of fixed-point free labeled packing.