[#SES-409] SPARQL OPTIONAL clause semantics not fully compatible

Issue Details [XML]

Key:	SES-409
Type:	Bug
Status:	Closed
Resolution:	Fixed
Priority:	Minor
Assignee:	Unassigned
Reporter:	Jeen Broekstra
Votes:	0
Watchers:	0

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Sesame

SPARQL OPTIONAL clause semantics not fully compatible

Created: 14/Jun/07 11:23 AM Updated: 20/Mar/08 08:41 PM

Component/s:

SPARQL

Affects Version/s:

2.0-beta5, 2.0-beta4

Fix Version/s:

2.0-beta6

Issue Links:

Dependency

This issue is a dependency for:
	~~SES-421~~ update SPARQL support to the CR of 14...

Description

SPARQL has adopted a semantics for the OPTIONAL clause which essentially reduces it a LeftJoin. In Sesame, we have an depth-first evaluation approach for SPARQL queries. In corner cases, this is not quite compatible with the official semantics of SPARQL.

The corner case is that of queries which contain patterns which are not "well designed". See http://iswc2006.semanticweb.org/items/Arenas2006bv.pdf : Perez. et al., "Semantics and Complexity of SPARQL", section 4.2, for a definition of this notion.

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Comment by Arjohn Kampman [07/Sep/07 11:38 AM]

The corner cases ("non well-designed graph patterns") are now handled differently by the generic query engine.