On 01/09/14 06:40, Wei Zhang wrote:
Hi All,
I want to parse the SPARQL query and get every element of a query and all the
features in order to rewrite the query. So I need to know all the triple
patterns and their level in the query.
For example, for a query like:
select * where {
{ bgp1}
UNION
{ bgp2.
bgp3}
OPTIONAL
{ bgp4}
}
I want to get bgp1-4, and also the relationships between them. e.g. bgp2 and
bgp3 is the conjunctive relationship. bgp1 and { bgp2. bgp3} are union
relationship.
Using algebra cannot get their relationships.
yes it can otherwise the query could not be executed.
SELECT *
WHERE
{ { { ?s1 ?p1 ?o1 }
UNION
{ ?s2 ?p2 ?o2 .
?s3 ?p3 ?o3
}
OPTIONAL
{ ?s4 ?p4 ?o4 }
}
}
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
(leftjoin
(union
(bgp (triple ?s1 ?p1 ?o1))
(bgp
(triple ?s2 ?p2 ?o2)
(triple ?s3 ?p3 ?o3)
))
(bgp (triple ?s4 ?p4 ?o4)))
Currently, I just decompose the first level as groups, then to find the pattern
in each element:
Query query = QueryFactory.create(strQuery);
Element qp = query.getQueryPattern();
List<Element> listElement = ((ElementGroup) qp).getElements();
for (int i = 0; i < listElement.size() ; i++){
Element e = listElement.get(i)
if ( e instanceof ElementUnion) {...}
if (e instanceof ElementGroup){...}
...
}
But there are two problems:
1) I cannot get further level of elements.
You need to recusive call your inspection code. It's need to do type
testing every time there is an Element.
Take the query example, {
bgp2. bgp3} is considered as one element and cannot be decomposed
further. But what I want is bgp2, bgp3 and their conjunctive relationship
It's an ElementPathBlock which has getPattern() to get the PathBlock
whch has .getList()
Everything is a path (a triple is a path of one step) in the grammar.
The algebra conversion sorts that out.
2) I cannot get subquery in this way. I found Andy said
ElementSubQuery can be used to get subquery
(https://www.mail-archive.com/[email protected]/msg06993.html) but I
cannot find more detailed documents or examples regarding to how to use
ElementSubQuery.
Its easier to look at the code - the syntax tree isn't complicated as
it's just a datastructure with very little algorithm.
ElementSubQuery.getQuery() -> Query
then call recursively, you code for looking in a query.
Andy
Could anyone help on this or give me any reference to use ElementSubQuery?
Thank you very much for your time and help!
Best Regards,
Wei Zhang
