  Graph database users today face a choice between two technology stacks: the
Resource Description Framework (RDF), on one side, is a data model with
built-in semantics that was originally developed by the W3C to exchange
interconnected data on the Web; on the other side, Labeled Property Graphs
(LPGs) are geared towards efficient graph processing and have strong roots in
developer and engineering communities. The two models look at graphs from
different abstraction layers (triples in RDF vs. edges connecting vertices with
inlined properties in LPGs), expose - at least at the surface - distinct
features, come with different query languages, and are embedded into their own
software ecosystems. In this short paper, we introduce a novel unifying graph
data model called Statement Graphs, which combines the traits of both RDF and
LPG and achieves interoperability at different levels: it (a) provides the
ability to manage RDF and LPG data as a single, interconnected graph, (b)
supports querying over the integrated graph using any RDF or LPG query
language, while (c) clearing the way for graph stack independent data exchange
mechanisms and formats. We formalize our new model as directed acyclic graphs
and sketch a system of bidirectional mappings between RDF, LPGs, and Statement
Graphs. Our mappings implicitly define read query semantics for RDF and LPGs
query languages over the unified data model, thus providing graph users with
the flexibility to use the query language of their choice for their graph use
cases. As a proof of concept for our ideas, we also present the 1G Playground;
an in-memory DBMS built on the concepts of Statement Graphs, which facilitates
storage of both RDF and LPG data, and allows for cross-model querying using
both SPARQL and Gremlin.
