Queries Across Sources
You've been told that SPARQL queries can allow you to query across sources, and that the
fd: in front of predicates meant
Fluree. Now, it's time to actually learn how to query across sources.
The concept is pretty simple: each triple refers to a particular dataset. A single triple cannot reference multiple datasets.
If every item in a triple is a variable, we assume that your datasource is Fluree, but you can specify otherwise by listing a prefix in front of any variable, for example
?creator fd:?label ?artwork.
The most up-to-date list of supported sources is available here.
In this lesson, we'll focus on three sources:
- The current Fluree
- The Fluree as of a given point in time
- Wikidata sources
There are multiple ways to specify Fluree, including
fdb. In order to use a Fluree as of a given block, simply add a number after the prefix, for example
The following query has triples that use the current Fluree as a source, as well as a previous version of the Fluree as a source:
SELECT ?person ?favNums
?person fd:person/favNums ?favNums;