Section: New Results

Knowledge Bases

Knowledge bases are collection of semantic facts (typically of the form subject–predicate–object) along with possible logical rules (e.g., in the form of existential rules) that apply to these facts. We investigate querying, data integration, and inference in such knowledge bases.

In [27], we focus on autocompletion of SPARQL queries over knowledge bases. We analyze several autocompletion features proposed by the main editors, highlighting the needs currently not taken into account while met by a user community we work with, scientists. Second, we introduce the first (to our knowledge) autocompletion approach able to consider snippets (fragments of SPARQL query) based on queries expressed by previous users, enriching the user experience. Third, we introduce a usable, open and concrete solution able to consider a large panel of SPARQL autocompletion features that we have implemented in an editor. Last but not least, we demonstrate the interest of our approach on real biomedical queries involving services offered by the Wikidata collaborative knowledge base.

In [25], we introduce a novel open-source framework for integrating the data of a user from different sources into a single knowledge base. Our framework integrates data of different kinds into a coherent whole, starting with email messages, calendar, contacts, and location history. We show how event periods in the user's location data can be detected and how they can be aligned with events from the calendar. This allows users to query their personal information within and across different dimensions, and to perform analytics over their emails, events, and locations. Our system models data using RDF, extending the schema.org vocabulary and providing a SPARQL interface.

Finally, in [22], [32], we view knowledge bases as composed of an instance that contains incomplete data and a set of existential rules, and investigate ontology-based query answering: answers to queries are logically entailed from the knowledge base. This brings to light the fundamental chase tool, and its different variants that have been proposed in the literature. It is well-known that the problem of determining, given a chase variant and a set of existential rules, whether the chase will halt on a given instance / on any instance, is undecidable. Hence, a crucial issue is whether it becomes decidable for known subclasses of existential rules. We consider linear existential rules, a simple yet important subclass of existential rules. We study the decidability of the associated chase termination problem for different chase variants, with a novel approach based on a single graph and a single notion of forbidden pattern. Besides the theoretical interest of a unified approach, an original result is the decidability of the restricted chase termination for linear existential rules.