Examples
Worked examples
- Is an instance
A DBpedia TPF endpoint allowing federated queries without running a heavyweight SPARQL endpoint.
- Is an instance
A research-information graph published as TPF for client-side joining with other LDF sources.
Counter-examples
Looks similar, but isn't
- Not an instance
A REST API returning JSON is not LDF.
- Not an instance
A static SPARQL dump alone is one extreme of the LDF spectrum, not the full LDF interface.
Editorial commentary
Introduced by Ruben Verborgh and colleagues, Linked Data Fragments (LDF) reframe RDF publishing as a spectrum of client-server query-cost trade-offs rather than a single fixed interface. At one extreme, a full SPARQL endpoint answers arbitrary, complex queries but concentrates all computational cost on the server, making it expensive to keep available under heavy public load. At the other extreme, a static RDF dump shifts all query work onto the client, which must download and index the entire dataset before it can ask anything. The intermediate Triple Pattern Fragments (TPF) interface answers queries restricted to a single triple pattern (subject-predicate-object, with wildcards), letting a federation of cheap, low-maintenance servers support globally-scaled federated SPARQL queries via client-side query planning that stitches many simple triple-pattern requests together.
Why the spectrum matters for research infrastructure
Research-data and knowledge-graph publishers (authority files, controlled vocabularies, linked open datasets built from CRIS or repository metadata) routinely find that a full public SPARQL endpoint is the interface researchers most want but the hardest and most expensive to keep continuously available — a small number of expensive queries can degrade or take down the service for everyone. LDF’s contribution is treating that trade-off as a design choice with named intermediate points, rather than an all-or-nothing decision between a fragile SPARQL endpoint and an unqueryable static dump.
Worked example
DBpedia has published a Triple Pattern Fragments endpoint alongside its full SPARQL endpoint specifically so that federated, cross-dataset queries can be answered even when the heavyweight SPARQL service is under load — a client library performs the query planning locally, issuing many simple triple-pattern requests to reconstruct the equivalent of a complex SPARQL query.
Counter-example
A plain REST API that returns JSON records by ID is not Linked Data Fragments, even if the underlying data model is RDF-based — LDF specifically describes interfaces built around the triple-pattern query primitive, not any API serving linked data in some form. Likewise, a static SPARQL results dump on its own is only one extreme point on the spectrum, not the LDF interface itself.
Related concepts
LDF sits alongside other lightweight metadata-exchange protocols research infrastructure relies on for similar reasons of server cost and availability, such as OAI-PMH for repository metadata harvesting, and is a relevant design reference when building or evaluating a PID graph or other queryable identifier infrastructure intended for public reuse.
References
- Verborgh, R., Vander Sande, M. et al., ‘Triple Pattern Fragments: A low-cost knowledge graph interface for the Web’, Journal of Web Semantics 37-38, 2016.
Also known as
LDF · Triple Pattern Fragments
Machine-readable encodings
Use in your systems
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