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streamreasoning / RSP-QL

A home of RSP-QL syntax and semantics discussion
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implementing Define isomorphism of RDF stream relative to sequence order #37

Closed greenTara closed 8 years ago

greenTara commented 8 years ago

Daniele - would you please review this pull request? Thanks!

dellaglio commented 8 years ago

The definitions are clear, but I have only one concern: can an RDF stream be infinite? If yes, the isomorphism on RDF streams is semi-decidable, as it is possible to state that two streams are not isomorphic, but not that they are isomprhic.

If what I wrote above is right, I would suggest to add a "practical" notion of isomorphism. That means, isomorphism on a window content (that is limited), or "isomorphism between streams up to time x".

greenTara commented 8 years ago

Yes, since an RDF stream is defined as a sequence, it can be either finite or infinite. The definition doesn't exclude it, so I suppose it could even be bi-infinite. Note that this is also true for RDF graphs (and datasets). An RDF graph is defined as a set of triples. There is no requirement that it be finite.

There is another section of the document that defines window functions (see https://github.com/streamreasoning/RSP-QL/pull/42). In some cases, the output of the window function will be finite. In those cases, the determination of isomorphism of the resulting streams is decidable. But just specifying a cutoff time is not enough to guarantee finiteness (e.g. Zeno's paradox).

I would be interested to see what practical kinds of isomorphism are needed.

dellaglio commented 8 years ago

Right, I was (wrongly) assuming that the time is defined in N. Thank you for the clarification

jpcik commented 8 years ago

31

greenTara commented 8 years ago

@dellaglio , @jpcik Can we merge this pull request now? I think the only outstanding question is a "practical" notion of isomorphism, and I think that is outside the scope of the original issue.

dellaglio commented 8 years ago

Yes, we can merge it.

Il Gio 3 Mar 2016 00:08 Tara Athan notifications@github.com ha scritto:

@dellaglio https://github.com/dellaglio , @jpcik https://github.com/jpcik Can we merge this pull request now? I think the only outstanding question is a "practical" notion of isomorphism, and I think that is outside the scope of the original issue.

— Reply to this email directly or view it on GitHub https://github.com/streamreasoning/RSP-QL/pull/37#issuecomment-191502851 .

Sent from my Android phone. Please excuse my brevity.

greenTara commented 8 years ago

close #31