I am in well over my head !
I can’t speak for the general case, but would a syntax something like…
results=ldp:contains[rdf:about is sys:Pug-2]/{(../rdf:about),
(cal:dtstart), (cal:dtend)}
Have expressed what I wanted per my original schema and grouped it the way I
wanted ?
Maybe at some point we run out of different types of parentheses ! And maybe
the ../ construct is playing too fast and loose with the path. Or is the
problem that somehow ../ is ambiguous in this environment ?
Many thanks
Alan
From: Sebastian Schaffert [mailto:sebastian.schaff...@gmail.com]
Sent: Friday, July 24, 2015 3:58 AM
To: users@marmotta.apache.org
Subject: Re: LDPath Query
2015-07-23 10:06 GMT+02:00 Sergio Fernández
<wik...@apache.org<mailto:wik...@apache.org>>:
Hi Alan
On Wed, Jul 22, 2015 at 9:16 AM, Robson, Alan
<alan.rob...@viasat.com<mailto:alan.rob...@viasat.com>> wrote:
I’d like a single query to return all the freezes for a system specified by its
fqdn in one shot (ie. if possible not have to query to collect the resources
with that fqdn (eg sys:Pug-2) followed by a separate query to get the freezes
that are rdf:about sys:Pug-2)
First of all LDPath is a resource-centered query language: you start with a
context resource and then you follow paths. For such kind of queries " return
all the freezes for a system" maybe SPARQL would give your better
expressiveness. Check it out in Marmotta, please.
I have two questions…
1) How can I select cal:dtstart and cal:dtend times for freezes belonging
to the freeze matching rdf:about[crtv:fqdn is "pug.local"] ? I can see how I
can select rdf:about, but not the other fields in the freeze record
Because at that point you already walked the path, you're already in the
rdf:about, and you can' t go back to the parent.
Jakob, do we have any trick for such construction?
This would require a *tree* query language, while LDPath is a *path* query
language. I was discussing the change to a tree language once with Jakob. It's
what I did more than 10 years ago for my PhD, so the algorithms are available.
It would, however, make the language syntax more complex because you'd need to
introduce variables that you bind, and your results would be result sets with
grouped variable bindings.
A trick that can be used is a concatenation of two subpaths using a function
that takes multiple arguments.
2) How can I group the results together ? If I mess with it I can get a
list of start times, a list of end times or even a big list of start and end
times mixed together, but I can’t figure a way to get a list of pairs of start
and end times that go together, one for each “Freeze”. Maybe I have just
structured the data wrongly.
This is actually the same question as 1, and the same answer.... ;-)
Sebastian
