◆ Semantic Web Catalogue

Problem thread

Querying a web, not a database

Can you query data spread across thousands of independent servers as if it were one database?

issue
scale & performance
also query & validation
status
open
steps
7, 2008–2025
threads
all problem threads

SPARQL gave RDF a query language, and the Linked Data vision implied that one query could reach across the whole Web of data. Link traversal and federated queries tried to make that real; monitoring then showed that public SPARQL endpoints were often unavailable or slow, and cheaper interfaces followed. In practice most querying still happens over central copies and crawls, and even the largest public endpoint has had to split its data to keep running.

Lineage

  1. 15 Jan 2008
    proposes standard ★ seminal
    SPARQL

    A query language for RDF data, a W3C Recommendation from January 2008. [src]

  2. Oct 2009
    proposes writing
    Executing SPARQL Queries over the Web of Linked Data

    Intertwine query evaluation with traversal of RDF links: URIs in partial results are looked up and the data they return is added, so there is no need to know all sources in advance. Waiting on lookups blocks execution, and completeness is hard to guarantee. [src1][src2]

  3. 21 Mar 2013
    proposes standard
    SPARQL 1.1

    Federated query: the SERVICE keyword sends part of a query to a remote SPARQL endpoint and combines its results with the rest. [src]

  4. Oct 2013
    measures writing ★ seminal
    SPARQL Web-Querying Infrastructure: Ready for Action?

    Monitoring of hundreds of public SPARQL endpoints finds many of them often unavailable, slow, or limited in what they will answer. [src]

  5. Mar 2016
    responds writing ★ seminal
    Triple Pattern Fragments: A Low-cost Knowledge Graph Interface for the Web
    ↳ responds to SPARQL Web-Querying Infrastructure: Ready for Action?

    Servers answer only simple triple patterns and clients do the rest, trading slower queries for servers that are cheap to keep available; it also queries federations of sources from the client. [src]

  6. 13 May 2019
    workaround writing
    Google Dataset Search: Building a search engine for datasets in an open Web ecosystem

    Finds datasets the way a search engine finds pages: by crawling their schema.org descriptions into one central index, rather than querying the sources live. [src]

  7. 9 May 2025
    measures project
    Wikidata Query Service

    The largest public SPARQL endpoint splits its graph: with more than 16 billion triples, its backend can no longer keep up, and scholarly articles move to a separate endpoint. Queries that need both must be federated. [src]

Recent signals

Dated events that show the problem moving, newest last.

  1. 17 Oct 2026

    The Wikidata Query Service is migrating to QLever, with pilot endpoints in testing. Wikidata Query Service[src]

Open now

Under each question, the answers people have put forward or built. The catalogue gives no odds on them.

  • Which queries over the open Web of data can be answered completely, and at what cost? [src]
    Hartig's later work shows that complete results over all Linked Data on the Web are likely infeasible, and that an iterator-based implementation of traversal querying cannot guarantee completeness.
  • Can public query services stay available as datasets grow into tens of billions of statements? [src1][src2]
    Endpoint monitoring in 2013 and Wikidata's graph split in 2025 point the same way.
    • Split the graph and switch to faster engines. Wikidata Query Service
      Wikidata split its graph in 2025 and is moving to QLever, the fastest engine in recent benchmarks.[src1][src2]

Forces

Pressures that push this problem one way or another, as their sources argue them. All forces

Decision points

Dated moments when a decision or a deadline can change the outcome.

  1. 1 Nov 2026
    New Wikidata query endpoints open service

    The QLever-based endpoints open to the community; the old Blazegraph endpoints may degrade from February 2027.[src]

How to contribute

  • Comunica repository

    Open-source framework for querying knowledge graphs from JavaScript, with packages for link-traversal querying and Triple Pattern Fragments. [src1][src2]

    checked 21 Oct 2026
  • Wikidata Query Service backend update forum · Wikidata Query Service

    Hub for moving the query service to QLever: early access to the new endpoints, office hours, and a place to submit hard use cases. [src]

    checked 21 Oct 2026