Hello Dave and Christopher,
Thank you very much for your clarifiying feedback. I had the notion of rdf:List
being a Container in my mind. All this led me to a helpful StackExchange topic:
https://stackoverflow.com/a/17589666/532272 . As I do not need finite
collections, I chose rdf:Seq although there might be advantages to rdf:List (I
just need control over the order of entries). The reason is mainly my
environment in which I generate RDF from XML via XSLT and parse it with Jena
for well formedness. So creating the rdf:List in Turtle, Ntriples or via API is
not an option. Further I learned that rdf:List is a nested structure rather
than a container - creating this via XSLT would be very cumbersome. In
contrary, creating a Seq container and filling this with rdf:li is very
convenient.
I have one question left: What is the best practice to dynamically recognize a
Seq? At the moment, I hardcoded the assumption that I got a Seq if the current
node isAnon(). This works with my data, but is obviously not very generic. Any
suggestions for improvements? Especially: Is there a Jena API call like
isResource(), isLiteral() -> isList(), isSeq(), ...?
Best Regards
Andreas
The Java Code reading the Seq is now this:
//Outer Method:
public Set<String> getLiteralsByPropertyURI(final String propertyUri) throws
TitleDataInvalidException {
final List<RDFNode> objectList = ...
//Keeps insertion order
final Set<String> output = new LinkedHashSet<>();
if (objectList != null && !objectList.isEmpty()) {
objectList.stream()
.filter(rdfNode -> null != rdfNode) //Filter out null
Objects as they will throw an NPE on TreeMap.compare()
.forEach(rdfNode -> {
//The Seq starts with an anon node
if (rdfNode.isAnon()) {
output.addAll(LDUtilities.getSeqItemsFrom(rdfNode));
} else if (rdfNode.isResource()) {
output.add(((Resource) rdfNode).getURI());
} else if (rdfNode instanceof Literal) {
output.add(((Literal) rdfNode).getLexicalForm());
}
});
}
return output;
}
//Inner Method:
protected static List<String> getSeqItemsFrom(final RDFNode node) {
final List<String> output = new ArrayList<>();
//Hardcoded as Seq:
final Seq seq = node.as(Seq.class);
final int x = seq.size();
for (int i = 1; i <= seq.size(); i++) {
final RDFNode object = seq.getObject(i);
if (object.isURIResource()) {
output.add(object.asResource().getURI());
} else if (object.isLiteral()) {
output.add(object.asLiteral().getLexicalForm());
}
}
return output;
}
>>> Christopher Johnson <[email protected]> 03.04.18 20.48 Uhr >>>
Hi,
My experience has informed me that a convenient way to create RDF Lists is
to start with JSON-LD. Here is the example:
{
"@context": {
"rdf": "http://www.w3.org/1999/02/22-rdf-syntax-ns#";
},
"@graph": [
{
"@id": "http://data.rism.info/id/rismauthorities/pe30077074";,
"http://umbel.org/umbel#isLike": {
"@list": [
"http://digital.slub-dresden.de/id339704470";,
"http://digital.slub-dresden.de/id313540659";,
"http://digital.slub-dresden.de/id307035654";
]
}
}
]
}
then as n-triples:
<http://data.rism.info/id/rismauthorities/pe30077074> <
http://umbel.org/umbel#isLike> _:b0 .
_:b0 <http://www.w3.org/1999/02/22-rdf-syntax-ns#first> "
http://digital.slub-dresden.de/id339704470"; .
_:b0 <http://www.w3.org/1999/02/22-rdf-syntax-ns#rest> _:b1 .
_:b1 <http://www.w3.org/1999/02/22-rdf-syntax-ns#first> "
http://digital.slub-dresden.de/id313540659"; .
_:b1 <http://www.w3.org/1999/02/22-rdf-syntax-ns#rest> _:b2 .
_:b2 d307035654" .
_:b2 <http://www.w3.org/1999/02/22-rdf-syntax-ns#rest> <
http://www.w3.org/1999/02/22-rdf-syntax-ns#nil> .
then as rdfxml:
*<?xml version='1.0' encoding='utf-8' ?>
<rdf:RDF xmlns:ns0='http://umbel.org/umbel# <http://umbel.org/umbel#>'
xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#
<http://www.w3.org/1999/02/22-rdf-syntax-ns#>'>
<rdf:Description
rdf:about='http://data.rism.info/id/rismauthorities/pe30077074
<http://data.rism.info/id/rismauthorities/pe30077074>'>
<ns0:isLike>
<rdf:Description rdf:nodeID='b0'>
<rdf:first>http://digital.slub-dresden.de/id339704470
<http://digital.slub-dresden.de/id339704470></rdf:first>
<rdf:rest>
<rdf:Description rdf:nodeID='b1'>
<rdf:first>http://digital.slub-dresden.de/id313540659
<http://digital.slub-dresden.de/id313540659></rdf:first>
<rdf:rest>
<rdf:Description rdf:nodeID='b2'>
<rdf:first>http://digital.slub-dresden.de/id307035654
<http://digital.slub-dresden.de/id307035654></rdf:first>
<rdf:rest
rdf:resource='http://www.w3.org/1999/02/22-rdf-syntax-ns#nil'/
<http://www.w3.org/1999/02/22-rdf-syntax-ns#nil'/>>
</rdf:Description>
</rdf:rest>
</rdf:Description>
</rdf:rest>
</rdf:Description>
</ns0:isLike>
</rdf:Description>
</rdf:RDF>*
As Dave indicates, creating lists in rdfxml is a bit of a pain.
Christopher Johnson
Scientific Associate
Universitätsbibliothek Leipzig
On 3 April 2018 at 17:09, Dave Reynolds <[email protected]> wrote:
> Hi,
>
> There seems to be a little confusion here.
>
> There are two mechanisms for representing ordered sequences of things in
> RDF. There are containers which come in three flavours one of which
> (rdf:Seq) is intended for ordered sequences:
>
> https://www.w3.org/TR/rdf-mt/#Containers
>
> There are also collections aka Lists:
>
> https://www.w3.org/TR/rdf-mt/#collections
>
> These are quite different both syntactically and semantically so you need
> to be clear on which one you are trying to use. Then the appropriate syntax
> and Jena API will follow.
>
> On 03/04/18 14:04, Andreas Kahl wrote:
>
>> Hello everyone,
>>
>> we have the requirement to preserve the order of umbel:isLike resources
>> and rdagr2:alternateIdentity literals in
>> https://data.rism.info/id/rismauthorities/pe30077074?format=rdf . To my
>> understanding, rdf:List would be a good choice. I followed the
>> recommendation at
>> http://patterns.dataincubator.org/book/ordered-list.html (data shortened
>> for brevity here):
>> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#";>
>> <rdf:Description rdf:nodeID="genid5">
>> <rdf:type
>> rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#List"/>
>> <rdf:li
>> rdf:resource="http://digital.slub-dresden.de/id339704470"/>
>> <rdf:li
>> rdf:resource="http://digital.slub-dresden.de/id313540659"/>
>> <rdf:li
>> rdf:resource="http://digital.slub-dresden.de/id307035654"/>
>> </rdf:Description>
>> <rdf:Description
>> rdf:about="http://data.rism.info/id/rismauthorities/pe30077074";>
>> <umbel:isLike xmlns:umbel="http://umbel.org/umbel#";
>> rdf:nodeID="genid5"/>
>> </rdf:Description>
>> </rdf:RDF>
>>
>
> This is not a list. You are using the syntax for Containers but trying to
> give it a type of rdf:List. This will not generate a legal list.
>
> Selecting this list via SimpleSelector and using Jena's RDFList fails
>> because no rdf:first & rdf:rest are found:
>>
>
> Correct, your data doesn't contain any lists.
>
> The only way of getting RDFList to work is adding
>> rdf:parseType='Collection'
>>
>
> Correct, if you are using RDF/XML that's the way to generate lists.
> However, you need to get the whole of the syntax right and you haveniteration
> (and not necessarily the
>> first).
>>
>
> Sounds like you haven't got the rest of the syntax right. For an example
> see:
> https://www.w3.org/TR/rdf-syntax-grammar/#section-Syntax-
> parsetype-Collection
>
> Note that this doesn't use the rdf:li syntax, that's for Containers not
> for Collections.
>
> W3C's validator says, the above rdf:List is valid RDF/XML.
>>
>
> It may be valid RDF/XML and it may mention rdf:List but it is not valid
> RDF/XML for a list :)
>
> Should I use another Java interface in Jena for this? Or do I have to
>> implement the list with more low level Jena calls avoiding the RDFList
>> interface? (e.g. iterating the _1, _2, _3, ...-Predicates with Selectors
>> myself)
>>
>
> The _1, _2 ... predicates are for Containers not Collections.
>
> I'd suggest picking which approach you want to use (ideally Lists but your
> choice), generating test cases in Turtle (*much* easier syntax when dealing
> with lists) and then use the corresponding Jena API (RDFList if you use
> lists). If you need to use RDF/XML then let the tools generate that for
> your from Turtle or from programmatic calls.
>
> Dave
>
>>
>> Thanks & Best Regards
>> Andreas
>>
>> P.S. My Jena dependency and version currently used:
>> <dependency>
>> <groupId>org.apache.jena</groupId>
>> <artifactId>apache-jena</artifactId>
>> <version>3.6.0</version>
>> <type>pom</type>
>> </dependency>
>>
>>
https://stackoverflow.com/a/17589666/532272
