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Balrog

Performing federated SPARQL queries is not always easy or doable. Public SPARQL end-points may not be properly configured, or they may time out too quickly for any meaningful federated query to be completed. Balrog aims at solving these issues using a local PostgreSQL installation to federate the result sets of two different end-points. (In some use cases, we even broke up an ordinary query into two queries for Balrog, in order to quickly work around some time-out issues on the public end-points of big triple stores, such as the one of Wikidata.)

Installation

You need Postgres 9+ already installed with user postgres, password postgres for a database called postgres.

npm install

Usage

npm start

Known bugs

  • Only bind with ?key
  • Only 2 endpoint
  • No others operands in the first level except for SERVICE
  • No operands in the most external SELECT except COUNT
  • Must use SELECT inside service
  • No *
  • An OPTIONAL without at least one value makes the code crash

Feature request

  • Better error comunication to the user
  • Automatically pagination (Virtuoso endpoints have limits e.g. 10k lines)
  • Smart VALUES usage for reduce complex queries and avoid timeouts
  • Don't use fs for passing CSV

Example working query

You can find some example of currently working federate SPARQL queries in the examples directory.

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The Dwarves delved too greedily and too deep. You know what they awoke in the darkness of Khazad-dûm...

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