OLAP Querying of Document Stores in the Presence of Schema Variety

Document stores are preferred to relational ones for storing heterogeneous data due to their schemaless nature. However, the absence of a unique schema adds complexity to analytical applications. In a previous paper we have proposed an original approach to OLAP on document stores; its basic idea was to stop fighting against schema variety and welcome it as an inherent source of information wealth in schemaless sources. In this paper we focus on the querying phase, showing how queries can be directly rewritten on a heterogeneous collection in an inclusive way, i.e., also including the concepts present in a subset of documents only.