Re: Linked Data Fragments: Web-scale querying

Ruben,

I'm implementing my own basic LDF server on top of some data I have. Questions:

1. Are the parameters standard? Do they have to be called
`?predicate=&subject=&object=`?
2. Is there a page somewhere that describes these parameters? For
example, how do I limit a specific set? Is there a `?limit=10`
parameter in the standard? And how would I do pagination? Ex: is there
`?offset=`?
3. In the paper it says "This would involve support for filters; one
way to implement them is to offer ldfs with regular expression
selectors. Such features would then also be indicated by a server.".
Again, is there a standard way of doing this and does basic LDF
enforce these rules are are they left to the server implementation?

Please have a look at https://github.com/kwijibo/trilby

What they do here is the implement basic triple matching patterns
directly as HTTP parameters. Here's a site using Trilby:
http://keithalexander.co.uk/ecco-tcp/

What I like about this is that it offers extra special parameters such
as `?_page=` but also filters like:
http://keithalexander.co.uk/ecco-tcp/?dct:date;_max=1795 using some
special path-based language that I'm not quite familiar with.

For now I'm not that interested in filters as complex as SPARQL
FILTERs, but more interested in providing at least pagination so was
wondering how basic LDF servers do that.

Thanks,
Luca

On Fri, Mar 21, 2014 at 3:03 PM, Olaf Hartig <ohartig@uwaterloo.ca> wrote:
> On Wednesday 19 March 2014 11:09:20 Kingsley Idehen wrote:
>> On 3/19/14 10:03 AM, Olaf Hartig wrote:
>> > Hi Martynas,
>> >
>> > On Wednesday 19 March 2014 12:58:15 Martynas Jusevičius wrote:
>> >> >Ruben,
>> >> >
>> >> >interesting stuff. I remember another project that does something like
>> >> >that: SQUINhttp://squin.sourceforge.net/index.shtml
>> >
>> > SQUIN implements a traversal-based query execution strategy that relies
>> > only on the Linked Data publishing principles (i.e., the possibility to
>> > look up HTTP URIs). Query processing approaches that have this property
>> > are typically referred to as Linked Data query processing. If you want to
>> > get an overview on these approaches, you may want to check out my recent
>> > survey [1].
>> >
>> >> >How does LDF compare to to it?
>> >
>> > I understand LDF more as an alternative practice for publishing (Linked)
>> > data on the Web. However, the primary purpose for proposing this practice
>> > (as Ruben and his colleagues emphasize in their LDOW paper) his to
>> > facilitate distributed querying without putting most of the burden on the
>> > servers.
>> >
>> > So, the primary difference between querying LDFs and the aforementioned
>> > Linked Data query processing is that querying LDFs is a form of
>> > distributed query processing, that is, some part of the execution of a
>> > given user query is distributed to LDF servers (which provide a limited
>> > form of query processing functionality). In contrast, Linked Data query
>> > processing  is_not_  a form of distributed query processing. Instead, for
>> > Linked Data query processing approaches, the whole execution of a query
>> > happens within the Linked Data query processing system (e.g., SQUIN),
>> > simply because these approaches do not assume / rely on server-side query
>> > processing functionality (servers in this setting are only required to
>> > answer URI lookup requests).
>> >
>> > Cheers,
>> > Olaf
>> >
>> >
>> > [1] Olaf Hartig: An Overview on Execution Strategies for Linked Data
>> > Queries. In Datenbankspektrum, 13(2) Jul. 2013.
>> > http://olafhartig.de/files/Hartig_LDQueryExec_DBSpektrum2013_Preprint.pdf
>>
>> Olaf,
>>
>> Is there a live showcase instance of SQUIN somewhere?
>
> I'm not maintaining any at the moment.
> Olaf
>
>

Received on Friday, 21 March 2014 16:42:22 UTC