Re: Getting Symmetric Concise Bounded Description with Fuseki

[Andy Seaborne]

Hi Reto,

The whole DescribeHandler system is very(, very) old and hasn't changed 
in ages, other than maintenance.


On 10/03/18 11:44, Reto Gmür wrote:

Hi Andy,

It first didn't quite work as I wanted it to: the model of the resource passed to the 
describe model is the default graph so I got only the triples in that graph.  Setting 
"tdb:unionDefaultGraph true" didn't change the graph the DescribeHandler gets.


tdb:unionDefaultGraph only affects SPARQL execution.


Looking at the default implementation I saw that the Dataset can be accessed 
from the context passed to the start method with 
cxt.get(ARQConstants.sysCurrentDataset). I am now using the Model returned by 
dataset. getUnionModel.


That should work.  Generally available getUnionModel post-dates the 
describe handler code.



I'm wondering why the DescribeBNodeClosure doesn't do the same but instead 
queries for all graphs that contain the resource and then works on each of the 
NamedModel individually. Is the UnionModel returned by the dataset inefficient 
that you've chosen this approach?


I don't think so - much the same work is done, just in different places.

getUnionModel will work with blank node named graphs.

getUnionModel will do describes spanning graphs, iterating over named 
graphs will not.



Also the code seems to assume that the name of the graph is a URI, does Jena not support 
Blank Nodes as names for graphs (having an "anonymous node" as name might be 
surprising but foreseen in RDF datasets)?


Again, old code (pre RDF 1.1, which is where bNode graph names came in).

Properly, nowadays, it should all work on DatasetGraph whose API does 
work with bNode graphs.  Again, history.


If you want to clean up, please do so.


It seems that even when a DescribeHandler is provided, the default handler is 
executed as well. Is there a way to disable this?


IIRC all the handers are executed - the idea being to apply all policies 
and handlers may only be able to describe certain classes.  Remove any 
not required, or set your own registry in the query (a bit tricky in 
Fuseki).



Another question is about the concept of "BNode closure", what's the rationale 
for expanding only forward properties? Shouldn't a closure be everything that defines the 
node?


It is a simple, basic policy - the idea being that more appropriate ones 
which are data-sensitive would be used. This basic one can go wrong 
(FOAF graphs when people are bnodes) and does not handle IFP; it does 
cover blank nodes used for values with structure and for RDF lists.


The point about DESCRIBE is that the "right" answer is not a fixed 
data-independent algorithm but is best for the data being published.


Andy



Cheers,
Reto


-Original Message-
From: Reto Gmür 
Sent: Friday, March 9, 2018 3:42 PM
To: users@jena.apache.org
Subject: RE: Getting Symmetric Concise Bounded Description with Fuseki

Great, it works!

Here's the code: https://github.com/linked-solutions/fuseki-scbd-describe

Cheers,
Reto


-Original Message-
From: Andy Seaborne 
Sent: Thursday, March 8, 2018 5:35 PM
To: users@jena.apache.org
Subject: Re: Getting Symmetric Concise Bounded Description with Fuseki



On 08/03/18 16:12, Reto Gmür wrote:

Thanks for the link ajs6f.

The described method for registering with the
DescribeHandlerRegistry

works if Fuseki is embedded. Is there a way to add a
DescribeHandlerFactory to a stand-alone fuseki instance? ServiceLoaders

come to mind.


ServiceLoaders, or use ja:loadClass.

https://jena.apache.org/documentation/notes/system-initialization.html



If there isn't such a possibility, what's the best way to embed
fuseki with the

full webapp (Fuseki UI and Admin functions)?




You just need to include it, set environment variables FUSEKI_HOME and
FUSEKI_BASE, put the files in the right place on disc

"$FUSEKI_HOME/webapp"

and call the main function.

org.apache.jena.fuseki.cmd.FusekiCmd.main(args ...)

  Andy


Cheers,
Reto


-Original Message-
From: ajs6f 
Sent: Saturday, March 3, 2018 5:13 PM
To: users@jena.apache.org
Subject: Re: Getting Symmetric Concise Bounded Description with
Fuseki

You can replace Jena's DESCRIBE behavior with whatever you like:

https://jena.apache.org/documentation/query/extension.html#describe
-
handlers

ajs6f


On Mar 3, 2018, at 8:03 AM, Reto Gmür 

wrote:


Hi all,

I've noticed that a DESCRIBE query returns the Concise Bounded
Description

(CBD) of a resource, i.e. it expands forward properties to the next
non-blank node. Is it possible to configure FUSEKI to also follow
properties backwards when answering a DESCRIBE query? Or is there
another query that would return that? By using the non-standard
possibility to query for blank-nodes I could get the full resource
context with multiple queries but I would refer to do this with a
single query

and not to use any non-standard SPARQL feature.


Cheers,
Reto

RE: Getting Symmetric Concise Bounded Description with Fuseki

[Reto Gmür]

Hi Andy,

It first didn't quite work as I wanted it to: the model of the resource passed 
to the describe model is the default graph so I got only the triples in that 
graph.  Setting "tdb:unionDefaultGraph true" didn't change the graph the 
DescribeHandler gets. 

Looking at the default implementation I saw that the Dataset can be accessed 
from the context passed to the start method with 
cxt.get(ARQConstants.sysCurrentDataset). I am now using the Model returned by 
dataset. getUnionModel.

I'm wondering why the DescribeBNodeClosure doesn't do the same but instead 
queries for all graphs that contain the resource and then works on each of the 
NamedModel individually. Is the UnionModel returned by the dataset inefficient 
that you've chosen this approach? Also the code seems to assume that the name 
of the graph is a URI, does Jena not support Blank Nodes as names for graphs 
(having an "anonymous node" as name might be surprising but foreseen in RDF 
datasets)?

It seems that even when a DescribeHandler is provided, the default handler is 
executed as well. Is there a way to disable this?

Another question is about the concept of "BNode closure", what's the rationale 
for expanding only forward properties? Shouldn't a closure be everything that 
defines the node?

Cheers,
Reto

> -Original Message-
> From: Reto Gmür 
> Sent: Friday, March 9, 2018 3:42 PM
> To: users@jena.apache.org
> Subject: RE: Getting Symmetric Concise Bounded Description with Fuseki
> 
> Great, it works!
> 
> Here's the code: https://github.com/linked-solutions/fuseki-scbd-describe
> 
> Cheers,
> Reto
> 
> > -Original Message-
> > From: Andy Seaborne 
> > Sent: Thursday, March 8, 2018 5:35 PM
> > To: users@jena.apache.org
> > Subject: Re: Getting Symmetric Concise Bounded Description with Fuseki
> >
> >
> >
> > On 08/03/18 16:12, Reto Gmür wrote:
> > > Thanks for the link ajs6f.
> > >
> > > The described method for registering with the
> > > DescribeHandlerRegistry
> > works if Fuseki is embedded. Is there a way to add a
> > DescribeHandlerFactory to a stand-alone fuseki instance? ServiceLoaders
> come to mind.
> >
> > ServiceLoaders, or use ja:loadClass.
> >
> > https://jena.apache.org/documentation/notes/system-initialization.html
> >
> > >
> > > If there isn't such a possibility, what's the best way to embed
> > > fuseki with the
> > full webapp (Fuseki UI and Admin functions)?
> > >
> >
> > You just need to include it, set environment variables FUSEKI_HOME and
> > FUSEKI_BASE, put the files in the right place on disc
> "$FUSEKI_HOME/webapp"
> > and call the main function.
> >
> > org.apache.jena.fuseki.cmd.FusekiCmd.main(args ...)
> >
> >  Andy
> >
> > > Cheers,
> > > Reto
> > >
> > >> -Original Message-
> > >> From: ajs6f 
> > >> Sent: Saturday, March 3, 2018 5:13 PM
> > >> To: users@jena.apache.org
> > >> Subject: Re: Getting Symmetric Concise Bounded Description with
> > >> Fuseki
> > >>
> > >> You can replace Jena's DESCRIBE behavior with whatever you like:
> > >>
> > >> https://jena.apache.org/documentation/query/extension.html#describe
> > >> -
> > >> handlers
> > >>
> > >> ajs6f
> > >>
> > >>> On Mar 3, 2018, at 8:03 AM, Reto Gmür 
> wrote:
> > >>>
> > >>> Hi all,
> > >>>
> > >>> I've noticed that a DESCRIBE query returns the Concise Bounded
> > >>> Description
> > >> (CBD) of a resource, i.e. it expands forward properties to the next
> > >> non-blank node. Is it possible to configure FUSEKI to also follow
> > >> properties backwards when answering a DESCRIBE query? Or is there
> > >> another query that would return that? By using the non-standard
> > >> possibility to query for blank-nodes I could get the full resource
> > >> context with multiple queries but I would refer to do this with a
> > >> single query
> > and not to use any non-standard SPARQL feature.
> > >>>
> > >>> Cheers,
> > >>> Reto
> > >