[Mulgara-general] walking bnodes?

tl thomas at stray.net
Wed Apr 30 18:41:58 UTC 2008

Am 29.04.2008 um 16:38 schrieb Paul Gearon:
> Hi,
> On Tue, Apr 29, 2008 at 8:38 AM, Alex Hall <alexhall at revelytix.com>  
> wrote:
>> On Tue, Apr 29, 2008 at 5:28 AM, tl <thomas at stray.net> wrote:
> <snip/>
>>> the question now is: is it possible to query for all predicates/
>>> objects of a given subject and let the query automagically follow  
>>> any
>>> _bnodes it encounters on the way? that's essentially the sparql
>>> DESCRIBE command [1] returning a Concise Bounded Description [2] i
>>> guess.
> Errrr, no. Have a look at DESCRIBE. It doesn't prescribe anything at
> all. It *might* do what you want here, but it really comes down to
> whatever the implementor felt like giving you when he wrote it.
> Note that the language says, "This data is not prescribed by a SPARQL
> query....", and, "The description is determined by the query service."
> The examples also use words like "may include", etc, etc.

i noticed that. the whole DESCRIBE is optional. i cited the spec  
because i hoped it could put in clearer words what i'm looking for.  
and i felt a little assured by the fact that the spec supports my  
point of view that recursively following the blank nodes would be a  
sensible way to gather information about a given subject.


>>> does TQL even provide the capability to identify a bnode and do
>>> something different in that case)?
>> TQL does provide a mechanism for discovering the type of nodes in a
>> graph using the nodetyping resolver [1].  Unfortunately, it does not
>> provide direct support for blank nodes; I believe this is a  
>> restriction
>> imposed by the internal architecture.
> It's not really imposed. I was just creating a way of identifying the
> "node type", and blank nodes don't really have a type. Since you can
> remove types with minus, I figured it was OK.
> It may be more convenient to check if something is a blank node
> explicitly, in which case I can probably add that. However, I don't
> have the time for it right now.

i'll remind you ;-)


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