Thanks Andy Everything I need to know was in your reply
Cheers, Rob On 7/7/13 7:57 AM, "Andy Seaborne" <[email protected]> wrote: >On 02/07/13 22:41, Rob Vesse wrote: >> I was wondering if anyone could enlighten me as to what the following >>algebra operators are supposed to represent, where I have at least a >>rough idea I have included my guess of the purpose but knowing for sure >>would be useful for something we're working on here atm >> >> OpList - something list related? >> OpDatasetNames - named graphs in the dataset? >> OpLabel - ?? >> OpDiff – some variant on OpMinus? >> >> Thanks, >> >> Rob >> > >(sorry - forgot to reply) > >** OpList - converts multiset of solution mappings (i.e. the result of >the WHERE clause) to sequence of solution mappings. The modifiers work >on sequences, joins etc work on multisets. > >http://www.w3.org/TR/sparql11-query/#defn_algToList > >Not really needed in ARQ as it represents multisets and sequnces via >iterators. > >** OpDatasetNames - needed in quad form for the case of > >GRAPH ?g {} >(and GRAPH <V> {} -- which is just a check) > >** OpLabel -- no-op : adds a label into the algebra expression for >labelling purposes. No computational effect. Seemed like it might be >useful when rewriting either to add explanations for humans or markers >to stop re-transforming recursively. > >** OpDiff -- not to do with Minus, it's in SPARQL 1.0 -- to do with >Optional in the strict SPARQL case. ARQ directly implements LeftJoin, >not as the expansion: > >LeftJoin(Ω1, Ω2, expr) = > Filter(expr, Join(Ω1, Ω2)) ∪ Diff(Ω1, Ω2, expr) > >http://www.w3.org/TR/sparql11-query/#defn_algLeftJoin >http://www.w3.org/TR/sparql11-query/#defn_algDiff > > Andy >
