RDF database systems form the largest subset of this last NoSQL category. RDF data can be thought of in terms of a decentralized directed labeled graph wherein the arcs start with subject URIs, are labeled with predicate URIs, and end up pointing to object URIs or scalar values.
Bottom line it sounds like there’s only one difference: standardization.
- A simple and uniform standard data model: all RDF database systems share the same well-specified and W3C-standardized data model at their base.
- A powerful standard query langauge: SPARQL is a very big win for RDF databases here, providing a standardized and interoperable query language that even non-programmers can make use of, and one which meets or exceeds SQL in its capabilities and power while retaining much of the familiar syntax.
- Standardized data interchange formats: RDF databases, by contrast, all have import/export capability based on well-defined, standardized, entirely implementation-agnostic serialization formats such as N-Triples and N-Quads.