We address the issue of Ontology-Based Data Access which consists of exploiting the semantics expressed in ontologies while querying data. Ontologies are represented in the framework of existential rules, also known as Datalog+/-. We focus on the backward chaining paradigm, which involves rewriting the query (assumed to be a conjunctive query, CQ) into a set of CQs (seen as a union of CQs). The proposed algorithm accepts any set of existential rules as input and stops for so-called finite unification sets of rules (fus). The rewriting step relies on a graph notion, called a piece, which allows to identify subsets of atoms from the query that must be processed together. We first show that our rewriting method computes a minimal set of CQs when this set is finite, i.e., the set of rules is a fus. We then focus on optimizing the rewriting step. First experiments are reported.
We address the issue of Ontology-Based Data Access, with ontologies represented in the framework of existential rules, also known as Datalog±. A wellknown approach involves rewriting the query using ontological knowledge. We focus here on the basic rewriting technique which consists of rewriting the initial query into a union of conjunctive queries. First, we study a generic breadth-first rewriting algorithm, which takes any rewriting operator as a parameter, and define properties of rewriting operators that ensure the correctness of the algorithm. Then, we focus on piece-unifiers, which provide a rewriting operator with the desired properties. Finally, we propose an implementation of this framework and report some experiments.
We address the issue of Ontology-Based Data Access, with ontologies represented in the framework of existential rules, also known as Datalog+/-. A well-known approach involves rewriting the query using ontological knowledge. We focus here on the basic rewriting technique which consists of rewriting a conjunctive query (CQ) into a union of CQs. We assume that the set of rules is a finite unification set, i.e., for any CQ, there exists a finite sound and complete rewriting of this CQ with the rules. First, we study a generic breadth-first rewriting algorithm, which takes as input any rewriting operator. We define properties of the rewriting operator that ensure the correctness and the termination of this algorithm. Second, we study some operators with respect to the exhibited properties. All these operators have in common to be based on so-called piece-unifiers but they lead to different explorations of the rewriting space. Finally, an experimental comparison of these operators within an implementation of the generic breadth-first rewriting algorithm is presented.
User-stories are commonly used to define requirements in agile project management. In Software Product Lines (SPL), a user-story corresponds to a feature description (or part of it), that can be shared by several products. In practice, large SPL include a huge number of user-stories, making variability hard to grasp and handle. In this paper we present an exploratory approach that aims to guide the synthesis of Feature Models that capture and structure the commonalities and the variability expressed in these user-stories. The built Feature Models aim to help the project understanding, maintenance and evolution. Our approach first decomposes the user-stories to extract the roles and the features, using natural language processing techniques. In a second step, we group userstories having the same topics thanks to a clustering method. This contributes to extract more general features. In a third step, we leverage the use of Formal Concept Analysis to extract logical constraints between the features that guide Feature Model synthesis. We illustrate our approach using a dataset from our industrial partner. CCS CONCEPTS• Software and its engineering → Software reverse engineering; Software configuration management and version control systems; Agile software development.
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