QB4OLAP: A New Vocabulary for OLAP Cubes on the Semantic Web

On-Line Analytical Processing (OLAP) tools allow querying large multidimensional databases called data warehouses (DW). OLAP-style data analysis over the semantic web (SW) is gaining momentum, and thus SW technologies will be needed to model, manipulate, and share multidimensional data. To achieve this, the definition of a precise vocabulary that adequately represents OLAP data on the SW is required. Unfortunately, so far, the proposals in this direction have followed different roads. On the one hand, the QB vocabulary (a proposal by the W3C Government Linked Data Working Group) follows a model initially devised for analyzing statistical data, but does not adequately support OLAP multidimensional data. Another recent proposal, the Open Cube vocabulary (OC) follows closely the classic multidimensional models for OLAP and allows implementing OLAP operators as SPARQL queries, but does not provide a mechanism for reusing data already published using QB. In this work, we propose a new vocabulary, denoted QB4OLAP, which extends QB to fully support OLAP multidimensional models and operators. We show how data already published in QB can be analyzed à la OLAP using the QB4OLAP vocabulary, and vice versa. To this end we provide algorithms that build the structures that allow performing both kinds of analysis, and show that compatibility between QB and QB4OLAP can be achieved at low cost, only adding schema information.