Hi Andy,
> On Feb 23, 2019, at 3:14 PM, Andy Seaborne <[email protected]> wrote:
>
> I thought xml:base has to be enabled in the RDF/XML writer, it's no on by
> default.
>
> https://jena.apache.org/documentation/io/rdfxml_howto.html#advanced-rdfxml-output
>
> <https://jena.apache.org/documentation/io/rdfxml_howto.html#advanced-rdfxml-output>
Ah! Thanks very much for pointing to docs on
org.apache.jena.rdf.model.RDFWriter . Indeed setting the “xmlbase” property
causes an xml:base to be included in the <rdf:RDF/> header as desired:
> org.apache.jena.rdf.model.RDFWriter rdfw = m.getWriter("RDF/XML");
> rdfw.setProperty("xmlbase", "http://purl.bdrc.io/ontology/ext/auth/";);
> rdfw.write(m, System.out, "http://purl.bdrc.io/ontology/ext/auth/";);
Are there any particular issues to be aware of when using
org.apache.jena.rdf.model.RDFWriter vs org.apache.jena.riot.RDFWriter which
underlies {Model, OntModel}.write? The latter doesn’t support a property to
include xml:base in the output.
>> However, we are wanting to ensure that there is an explicit baseURI present
>> in the resulting serialization.
>
> Out of curiosity, why do you want that?
>
> Using ":" instead of a "base" seems quite common.
There are third party tools, such as TopBraid Composer FE, SE and ME, that
require an explicit xml:base when resolving an owl:imports via the web - i.e.,
there is no matching local file - rather than using the URI in the owl:imports
as the baseURI for the document. As I read the RDF/XML syntax spec the client
is supposed to use the document URL for the baseURI when no xml:base is
present. The TBC uses an "Accept: application/rdf+xml, text/turtle” and with
such a list RDF/XML is selected (the service can provide both serializations).
A solution, when serializing as RDF/XML, might be to use
Model.write(OutputStream, “RDF/XML", null) or Model.write(OutputStream,
“RDF/XML”), which forces absolute paths to be used in the output; however,
without the (unnecessary) xml:base, TBC fails silently to load the imports. By
comparison, Protégé has no problem correctly following owl:imports.
We’re just trying to provide proper content negotiation and accommodate the
dictum that the client makes it right.
Based on the javadoc for Model.write parameter, base:
> base The base uri to use when writing relative URI's. null means use only
> absolute URI's. This is used for relative URIs that would be resolved against
> the document retrieval URL. For some values of lang, this value may be
> included in the output.
It is unclear of what use a non-null value for XML/RDF is since the resulting
output has no xml:base, the URL of the doc can not be necessarily relied on,
and the output is rendered ambiguous since relative URIs can’t be resolved
unless perhaps the default namespace, denoted by “:”, is used..
The write w/ an explicit baseURI could output an explicit xml:base (as an @base
is written for Turtle) or as also suggested by the javadoc simply use the
supplied baseURI to construct the proper URIs for values of rdf:about etc on
output.
> Andy
Thank you,
Chris
>
> On 23/02/2019 00:42, Martynas Jusevičius wrote:
>> Sorry, can't run the test case right now.
>> No I'm thinking RDF/XML :) But the prefixes are only used for
>> properties, not subject (@rdf:about) or object (@rdf:resource) values.
>> What would you gain by adding an xml:base? You could shorten
>> prfx:lcl-name to just lcl-name by setting xml:base to prfx: namespace
>> URI, but that would only work for a single namespace.
>> And not sure how much sense it makes to compare RDF/XML with Turtle
>> because the former builds on XML which has its own namespace
>> mechanism. But maybe I'm completely misunderstanding what you are
>> trying to do :)
>> On Sat, Feb 23, 2019 at 12:18 AM Chris Tomlinson
>> <[email protected]> wrote:
>>>
>>> No.
>>>
>>> If you run the test case you see that RDF/XML writes out xmlns defns of
>>> prefixes and uses the prefixes in the serialization. Perhaps you are
>>> thinking of n-triples.
>>>
>>> Thanks,
>>> Chris
>>>
>>>> On Feb 22, 2019, at 16:52, Martynas Jusevičius <[email protected]>
>>>> wrote:
>>>>
>>>> Isn't it so that RDF/XML writer always writes absolute URIs, so
>>>> xml:base is unnecessary because it would have no effect anyway?
>>>>
>>>> On Fri, Feb 22, 2019 at 11:20 PM Chris Tomlinson
>>>> <[email protected]> wrote:
>>>>>
>>>>> Hello,
>>>>>
>>>>> We are trying to serve various ontology files in a variety of
>>>>> serializations, principally RDF/XML and Turtle.
>>>>>
>>>>> The specs indicate that if the baseURI for an ontology is the URL by
>>>>> which the ontology is retrieved then it is not required that the producer
>>>>> include an explicit xml:base or @base or similar in the serialization.
>>>>>
>>>>> However, we are wanting to ensure that there is an explicit baseURI
>>>>> present in the resulting serialization.
>>>>>
>>>>> This is because not all tools respect the injunction to use the URL that
>>>>> was used to retrieve the ontology as the baseURI if there is not an
>>>>> explicit xml:base or @base and so on in the serialization.
>>>>>
>>>>> The question is that Model.write(OutputStream, Language, baseURI)
>>>>> includes an @base when the language is “TURTLE“ in the serialization but
>>>>> when the language is “RDF/XML” we do not see an xml:base in the result.
>>>>> (same happens when OntModel is used and when RDFWriter is used.)
>>>>>
>>>>> The docs indicate that the baseURI param is to be used to specify what
>>>>> URI should be used to serialize relative URIs and says nothing about
>>>>> including xml:base or @base; yet, we see the @base for Turtle and no
>>>>> xml:base for RDF/XML.
>>>>>
>>>>> This is an issue when a tool requests RDF/XML before Turtle in accept
>>>>> headers and requires that there be an xml:base in the RDF/XML
>>>>> serialization. Noting that RDF/XML is the only required serialization.
>>>>>
>>>>> What procedure should be used to “force” an @base or xml:base uniformly?
>>>>>
>>>>> Here is a small test case that shows the issue:
>>>>>
>>>>>
>>>>> https://github.com/buda-base/lds-pdi/blob/master/src/test/java/io/bdrc/ldspdi/test/ModelWriteTest.java
>>>>>
>>>>> <https://github.com/buda-base/lds-pdi/blob/master/src/test/java/io/bdrc/ldspdi/test/ModelWriteTest.java>
>>>>>
>>>>>
>>>>> Thank you,
>>>>> Chris
>>>>>
>>>>>
