Guillaume Bagan

Generating flexible workloads for graph databases

Graph data management tools are nowadays evolving at a great pace. Key drivers of progress in the design and study of data intensive systems are solutions for synthetic generation of data and workloads, for use in empirical studies. Current graph generators, however, provide limited or no support for workload generation or are limited to fixed use-cases. Towards addressing these limitations, we demonstrate gMark, the first domain- and query language-independent framework for synthetic graph and query workload generation. Its novel features are: (i) fine-grained control of graph instance and query workload generation via expressive user-defined schemas; (ii) the support of expressive graph query languages, including recursion among other features; and, (iii) selectivity estimation of the generated queries. During the demonstration, we will showcase the highly tunable generation of graphs and queries through various user-defined schemas and targeted selectivities, and the variety of supported practical graph query languages. We will also show a performance comparison of four state-of-the-art graph database engines, which helps us understand their current strengths and desirable future extensions.

Efficient enumeration for conjunctive queries over x-underbar structures

We investigate efficient enumeration algorithms for conjunctive queries for databases over binary relations that satisfy the X property. Treelike relations such as XPath axes or grids are natural examples of such relations. We first show that the result of an n-ary conjunctive query Q over an X structure S can be enumerated with a delay in O(n ċ |S| ċ |Q|) between two consecutive n-tuples. Then, we consider acyclic conjunctive queries and show that such queries admit an enumeration algorithm with delay O(|Q| ċ |D|) and a preprocessing in O(|Q| ċ |S|) where D is the domain of S. The delay can even be improved to O(n ċ |D|) with a slightly more expensive preprocessing step. As an application of our method, we also show that any n-ary XPath acyclic conjunctive query Q over an unranked tree t can be enumerated with a preprocessing and delay O(|Q| ċ |t|). In the second part of the paper, we consider conjunctive queries with possible inequalities (≠) between variables. In this case, we show that query evaluation is NP-hard and, unless P = NP, these queries do not admit enumeration algorithms with a combined polynomial time delay. However, we also show that hardness relies only on the number l of variables that appear in inequalities. We propose efficient enumeration procedures for acyclic and general conjunctive queries whose delay is exponential in l but polynomial (even quasi-linear) in |Q| and |S|.

gMark: Schema-Driven Generation of Graphs and Queries

Abstract-Massive graph data sets are pervasive in contemporary application domains. Hence, graph database systems are becoming increasingly important. In the experimental study of these systems, it is vital that the research community has shared solutions for the generation of database instances and query workloads having predictable and controllable properties. We present the design and engineering principles of gMark, a domain- and query language-independent graph instance and query workload generator. A core contribution of gMark is its ability to target and control the diversity of properties of both the generated instances and the generated workloads coupled to these instances. Further novelties include support for regular path queries, a fundamental graph query paradigm, and schema-driven selectivity estimation of queries, a key feature in controlling workload chokepoints. We illustrate the flexibility and practical usability of gMark by showcasing the framework’s capabilities in generating high quality graphs and workloads, and its ability to encode user-defined schemas across a variety of application domains.

On some domination colorings of graphs

Abstract In this paper, we are interested in four proper vertex colorings of graphs, with additional domination property. In the dominator colorings, strong colorings and strict strong colorings of a graph G , every vertex has to dominate at least one color class. Conversely, in the dominated colorings of G , every color class has to be dominated by at least one vertex. We study arbitrary graphs as well as P 4 -sparse graphs, P 5 -free graphs, bounded treewidth graphs and claw-free graphs.

Edge Monitoring Problem on Interval Graphs

Abstract Edge monitoring is a simple and effective mechanism for the security of wireless sensor networks. The idea is to award specific roles (monitors) to some sensor nodes of the network. A node v monitors an edge e if both extremities together with v form a triangle in the graph. Given an edge colored graph G = ( V , E , c ) , the color c ( e ) is a positive integer representing the number of monitors needed by the edge e. The problem is to seek a minimum cardinality subset of monitors S such that every edge e in the graph is monitored by at least c ( e ) vertices in S. If vertices of G are weighted, the objective then is to minimize the total weight of vertices of S and the problem is called weighted edge monitoring problem. In this paper, we present a polynomial-time algorithm for finding an edge monitoring set of minimum weight in interval graphs.