Re: (non-)shrinking semantics of aggregates

Dear Peter,

I think [2] is a wrong reference. It should point to the C-SPARQL paper I’m attaching. In particular you should read section 3.4 where the “original” C-SPARQL aggregates are presented. Either there, the word “ shrinking” is not used since it emerged later on in the C-SPARQL research.

To give you the intuition, SQL and SPARQL aggregates are “shrinking” because they compute aggregates and the solution mappings they come from disappear.

The “original” C-SPARQL aggregates decorate each solution mapping with the computed aggregates without “shrinking” the result.

The “original” C-SPARQL aggregates were proposed before SPARQL 1.1, where the aggregates were standardised, and after a long discussion with the SPARQL 1.1 working group, we agreed that SPARQL 1.1 combining aggregates and subqueries can generate the same answers of the “original” C-SPARQL aggregates. Indeed, the “original” C-SPARQL aggregates are only an handy syntax that avoids using subqueries explicitly to obtain the non-“shrinking” semantics.

I’m available for further discussion if needed.

Best Regards,

Emanuele

On 18 Feb 2016, at 09:20, Wetz Peter <peter.wetz@tuwien.ac.at<mailto:peter.wetz@tuwien.ac.at>> wrote:

Hi all,

I hope someone of you can help in answering my question: In [1] (e.g. page 8 and 11) I read about “shrinking” and “non-shrinking semantics” of aggregates with a reference to the paper at [2]. However, in [2] the word “shrinking” does not appear a single time.

So I wonder, if the reference is a mistake, or maybe I’m just blind and can’t find the explanation in [2]. After all, I just would like to know where to find a proper definition of shrinking and non-shrinking semantics.

Thanks!

[1] Scharrenbach, T., Urbani, J., Margara, A., Della Valle, E., & Bernstein, A. (2013). Seven commandments for benchmarking semantic flow processing systems. In The Semantic Web: Semantics and Big Data (pp. 305-319). Springer Berlin Heidelberg. URL: http://eswc-conferences.org/sites/default/files/papers2013/scharrenbach.pdf

[2] Barbieri, D. F., Braga, D., Ceri, S., Della Valle, E., & Grossniklaus, M. (2010). Incremental reasoning on streams and rich background knowledge (pp. 1-15). Springer Berlin Heidelberg. Chicago. URL: http://kops.uni-konstanz.de/bitstream/handle/123456789/25310/Barbieri_253103.pdf


Best,
Peter

--
Emanuele Della Valle, PhD
DEIB - Politecnico di Milano
m. +393389375810
w. http://emanueledellavalle.org