Semantics of SPARQL 1.1 aggregates

Hi,

I am trying to understand the semantics of aggregates. However, the
explanation in 'SPARQL 1.1 Query Language. W3C Recommendation 21 March
2013' (especially in Section 18.2.4.1 Grouping and Aggregation), is
confusing. Could someone explain either in plain English or in a more
formal way than in SPARQL specification, how aggregates are supposed to
work?

Some specific questions:

1) In Step: Aggregates, which variables are referred in

'For each variable V appearing outside of an aggregate'

2) Are arbitrary expressions allowed as actual parameters in aggregate
calls? Is AVG(?x/10) legal? What about nested aggregates, e.g., in the
following, somewhat strange query:

PREFIX :<http://example.org/#>

SELECT ?w (MAX(?w/(AVG(?h/100)*AVG(?h/100))) as ?m) {
       ?p :weigth ?w ; :height ?h .
} GROUP BY ?w


/Esko
-- 
Esko Nuutila
Aalto University School of Science and Technology
Department of Computer Science and Engineering
P.O.Box 15400 (T-building, Konemiehentie 2, room B218)
FI-00076 AALTO, FINLAND
tel. +358 50 5750278 mailto: esko.nuutila@aalto.fi