rdfapi-php-interest

[Rdfapi-php-interest] explicit individual statement reification

[Saf H. <saf...@gm...>]

Hi,

New to RDF and PHP so this may be a simple syntax issue:

Having consulted the tutorials and class details for statements, I'm
still unclear as to how to set the label of a statement. I don't want
to use the system-generated numbers e.g. by reifying a whole model - I
just want to give my statements names of my choice.
e.g.
<a><b><c>   reify as:   'Matilda'
results in:
<Matilda><type><statement>
<Matilda><subj><a>
<Matilda><pred><b>
<Matilda><obj><c>

I keep getting an error message regarding not being able to pass
parameter 1 e.g. 'Matilda' whenever I use
$statement_x->reify("Matilda");

Please could someone provide a worked example?

I'm assuming 'Matilda' will be regarded as both a uri and url for this
statement resource, like any other type of resource. Is this true?

Thanks

Saf

Re: [Rdfapi-php-interest] explicit individual statement reification

[Richard C. <ri...@cy...>]

Hi Saf,

On 15 Sep 2005, at 11:07, Saf Hulou wrote:

> Hi,
>
> New to RDF and PHP

Welcome!

> so this may be a simple syntax issue:
>
> Having consulted the tutorials and class details for statements, I'm
> still unclear as to how to set the label of a statement. I don't want
> to use the system-generated numbers e.g. by reifying a whole model - I
> just want to give my statements names of my choice.

Okay. If you reify a statement, you say that a *resource* represents  
the statement.

Let me repeat: A reified statement is not a "label" for a statement,  
it's a resource representing the statement. So it can be a URI or a  
blank node, but not a simple string.

> e.g.
> <a><b><c>   reify as:   'Matilda'
> results in:
> <Matilda><type><statement>
> <Matilda><subj><a>
> <Matilda><pred><b>
> <Matilda><obj><c>

'Matilda' is a string. A reified statement can be a URI or a blank  
node, but not a string.

> I keep getting an error message regarding not being able to pass
> parameter 1 e.g. 'Matilda' whenever I use
> $statement_x->reify("Matilda");

You have to pass a model or a blank node. Passing a string doesn't work.

> Please could someone provide a worked example?
>
> I'm assuming 'Matilda' will be regarded as both a uri and url for this
> statement resource, like any other type of resource. Is this true?

You really have to be more clear about the difference between URIs  
and simple strings.

If you want to assign a simple string as a label to a reified  
statement, you can create an RDF graph like this:

_:blank rdf:type rdf:Statement .
_:blank rdf:subject :a .
_:blank rdf:predicate :b .
_:blank rdf:object :c .
_:blank rdfs:label "Matilda" .

(This is Turtle syntax)

_:blank is the blank node representing the statement. All the other  
things with ":" in them are URIs (abbreviated as QNames). The  
rdfs:label triple assigns a label to the reified statement.

That said, the reification support in RAP is clunky. Apparently  
there's no way to create a reified statement from a URI, you have to  
use a blank node. That's a limitation of RAP; RDF allows it.

I probably caused more confusion than clarity with this response.  
Sorry about that!

All the best,
Richard


>
> Thanks
>
> Saf
>
>
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[Rdfapi-php-interest] Re: explicit individual statement reification

[Saf H. <saf...@gm...>]

Hi Richard,

Thank you for your reply.

The last point - rap won't let me create a reified statement from a
uri is precisely my problem.

Sorry about the confusion with 'Matilda'. I used the string because I
couldn't see the difference (as far as RDF is concerned) between
'Matilda' and ' http://www.my_statements.com/matilda'.

It seems that I will have to create the blank node and create a  label
for the blank node, as you suggest. This is a bit wierd though.
How do I pass a blank node id or a model to a reify function?=20
Isn't it a bit meaningless to create a blank node or model before I've
reified the statement? Are they simply  placeholders?

I think I'm misunderstanding something here....

Re: [Rdfapi-php-interest] Re: explicit individual statement reification

[Richard C. <ri...@cy...>]

Hi Saf,

Sorry for the long delay.

On 16 Sep 2005, at 13:10, Saf Hulou wrote:
> The last point - rap won't let me create a reified statement from a
> uri is precisely my problem.

Ah, I see. It's a RAP limitation.

> It seems that I will have to create the blank node and create a  label
> for the blank node, as you suggest. This is a bit wierd though.
> How do I pass a blank node id or a model to a reify function?

When you pass a blank node, then that blank node will simply be used  
as the subject of the four reification statements. To create a blank  
node, do "$blank = new BlankNode($model)".

What happens when you pass a model is this: RAP creates a new blank  
node, which becomes the representation of the reified statement. The  
model is needed only because of the way RAP creates blank nodes. RAP  
uses the model to make sure that the blank node is unique (within  
that model).

Don't you have a model anyway where your statements are stored? You  
just can use that model as the argument to $statement->reify. You  
don't have to create a new model.

> Isn't it a bit meaningless to create a blank node or model before I've
> reified the statement? Are they simply  placeholders?

As I said, you don't have to create the blank node yourself. The  
reify method can create it for you. However, you have to pass in some  
model because RAP needs one to create unique blank nodes. Don't pass  
a new model every time, but re-use the model you're working with anyway.

> I think I'm misunderstanding something here....

Sorry about that. RAP's reification support is a bit strange and  
doesn't seem to be used very much.

I think what you probably want to do is this:

    $new_blank_node = $model->reify_statement($statement)

This would create a new blank node and it would add the four  
reification statements to $model.

In RAP you have to do this to get the same effect:

    $new_blank_node = new BlankNode($model)
    $reification_quad = $statement->reify($new_blank_node)
    $model->addModel($reification_quad)

(But this doesn't work currently because of a bug, I'll send a  
separate mail about that.)

Hope that helps.
Richard



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