Integrating nested data into knowledge graphs with RML fields

Thomas Delva, Dylan Van Assche, Pieter Heyvaert, Ben De Meester, Anastasia Dimou

Keywords: RML, nested data, KGC challenges

TL;DR: An extension which empowers RML to integrate nested data into knowledge graphs

Abstract:

To support business decisions or improve operational efficiency,
heterogeneous data is often integrated into a knowledge graph. This inte-
gration can be achieved with one of the existing declarative mapping lan-
guages, which offer declarative data integration in the form of knowledge
graphs. However, current mapping languages cannot always integrate
data with nested structure, such as JSON or XML files or JSON docu-
ments stored in a database column. We designed a backwards-compatible
extension of the RDF Mapping Language (RML) which empowers it to
integrate nested data: RML fields. In this paper, we introduce RML fields,
compare it with the state of the art in mapping languages, and validate
it on mapping challenges formulated by the Knowledge Graph Construc-
tion W3C community group. Our extension allows to address several of
the challenges related to nested data that were previously not possible.
RML fields can be used to integrate even more datasets into knowledge
graphs with all the advantages of using a language specially designed for
that purpose. Our extension currently is intended to integrate multiple
data sets independently, but some use cases require joins or other oper-
ations during knowledge graph generation, which we will investigate in
the future.