Suggestion: Dereferencing of URIs used in FROM and FROM Named clauses without corresponding graphs in the dataset

[MaillPierre]

As seen in a previous issue, Corese has implemented a dereferencing mechanism that uploads a file as a graph. This mechanism could be implemented to dereference URIs used in SPARQL queries in FROM and FROM NAMED clauses.

Detailed Description

In the SPARQL norm, the dereferencing of URIs in FROM and FROM NAMED clauses is left to the implementor. Only security remarks are left as information for the implementation of the norm.
Currently, Corese already implements a dereferencing and loading mechanism for files that contain the owl:imports property.
This mechanism could be transposed to SPARQL queries when a FROM clause is given but does not name an existing graph.

Context

The implementation of this mechanism would make it possible to test the dereferencability of URIs. In best practices for Linked Data, URIs are encouraged to be dereferenceable but no way to verify or take advantage of that is available is SPARQL. With this change in Corese, one could test if the graph resulting from the dereference of a URI contains any triples, and deduce if the URI can be dereferenced or not.

Furthermore, the SPARQL-SD and the VoID define ways to retrieve metadata descriptions, of SPARQL endpoints and datasets respectively, hosted in an RDF document. Despite their usefulness, those descriptions are not natively usable in SPARQL queries. With the proposed change, one could make SPARQL that adapt themselves to a SPARQL server or a dataset according to their self-descriptions.

Possible Implementation

A security audit of possible ways to abuse this mechanism is necessary. The mechanism of file retrieval and load as it exists seems usable as is. If the URI given correspond to an existing graph, then no dereferencing should be done, and the query should be executed as done currently.

Your Environment

• Version used: Server
• Server type and version: 4.4.0
• Operating System and version: Linux
• Link to your project: https://github.com/Wimmics/IndeGx

[ocorby]

Hello, Corese provides the statement below to dereference an URI: bind (xt:load(URI) as ?g)graph ?g { BGP } Regards Olivier

[MaillPierre]

This work for my use case, while I wait for the implementation of the suggestion ;)

Thanks