just some comments as you already got the answer:
pagination in SPARQL can only be done via limit + offset, as you already
have figured out - but, formally, it is only guaranteed to be correct
when sorting the data.
depending on the size of the data this can be expensive - especially
what people always find strange is hat offset operator in SPARQL is not
as simple as it might be in SQL because of the semantics of SPARQL.
There isn't a "simple" cursor like in SQL database, so it might be
rather slow for large offsets.
Jena usually doesn't know the result size during query execution as it's
(afaik) using a pipelined execution (aka lazy or Volcano) - only for
operations where it has to have to whole intermediate result computed to
proceed to the next stage (e.,g. aggregates) this assumption holds.
long story short: if you really think that a user needs to see all
pages, as already suggest, a count in a separate query before would do it.
On 09.03.21 09:52, Donald McIntosh wrote:
Hi..
I have an implementation where I would like to page through data retrieved via
a SPARQL query on Apache Jena on a UI. offset and limit features take me some
of the way there but do not tell me the full size of the overall result set so
that users can skip to the end or to page x knowing that it will exist. I am
guessing that internally Jena will know the result set size from a query but
perhaps this not available to the caller, as the full set will have been
retrieved and sorted.
Is there a correct and efficient way to implement this type of use case
inApache Jena ?
Thanks,
Donald
