Support sequence keyword

[keski]

Issue by keski
Thursday Feb 04, 2016 at 11:05 GMT
_Originally opened as _

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The sequence keyword has been discussed as an extension to support CEP operators in the RSP-QL. Although this may not be supported in the standard version of the RSP-QL extensions are likely to use the same format as EP-SPARQL and CQELS. Sequence has been noted as the most important operator on several occasions.

Example 1 (based on CQELS syntax):

WHERE {
   WINDOW :w {
      { :car1 :observedBy :cam1 }
      SEQ
      { :car1 :observedBy :cam2 }
   }
}

Example 2 (sequencing with graphs):

WHERE {
   WINDOW :w {
      GRAPH ?g1 { :car1 :observedBy :cam1 }
      SEQ
      GRAPH ?g2 { :car1 :observedBy :cam2 }
   }
}

Example 3 (sequencing using windows):

WHERE {
   WINDOW :w1 { GRAPH ?g1 { :car1 :observedBy :cam1 } }
   SEQ
   WINDOW :w2 { GRAPH ?g2 { :car1 :observedBy :cam2 } }
}

Should all formats be supported?

Example 1 is excluding the named graph. This assumes that the window graphs are put in a single graph but that (somehow) ordering can still be retrieved on a triple level. Or is this just syntactic sugar?

Example 2 is a more general form of example 1 that does not require merging graphs. This is needed for complex event processing.

Example 3 is the most flexible but quickly becomes very verbose if used to sequence within the same window.