How to retrieve a RDF Property

I have this piece of information in RDF/XML

<rdf:RDF xmlns:cim="http://iec.ch/TC57/2012/CIM-schema-cim16#" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
 <cim:SynchronousMachineTimeConstantReactance rdf:ID="_54302da0-b02c-11e3-af35-080027008896">
  <cim:IdentifiedObject.aliasName>GENCLS_DYN</cim:IdentifiedObject.aliasName>
  <cim:IdentifiedObject.name>RoundRotor Dynamics</cim:IdentifiedObject.name>
  <cim:SynchronousMachineTimeConstantReactance.tpdo>0.30000001192092896</cim:SynchronousMachineTimeConstantReactance.tpdo>
  <cim:SynchronousMachineTimeConstantReactance.tppdo>0.15000000596046448</cim:SynchronousMachineTimeConstantReactance.tppdo>

I have learned a little bit about how to read the document but now I want to go farther. I am "playing" with API functions to try to get the values but I am lost (and I think I do not understand properly how JENA and RDF work). So, how can I get the values of each tag?

Greetings!

Solution

I would start with the Reading and Writing RDF in Apache Jena documentation, and then read The Core RDF Api. One important step in understanding the RDF Data Model is to seperate any notion of XML from your understanding of RDF. RDF is a graph data model that just so happens to have one serialization which is in XML.

You'll note that xml-specific language like "tags" actually don't show up at all in the discussion unless you are talking about how to serialize/deserialize RDF/XML.

In order to make the data you are looking at more human friendly, I'd suggest writing it out in TURTLE. TURTLE (or TTL) is another serialization of RDF that is much easier to read or write.

The following code will express your data in TURTLE and will be helpful in understanding what you see.

final InputStream yourInputFile = ...;
final Model model = ModelFactory.createDefaultModel();
model.read(yourInputFile, "RDF/XML");
model.write(System.out, null, "TURTLE");

You'll also want to provide minimal working examples whenever submitting questions on the subject area. For example, I had to add some missing end-tags to your data in order for it to be valid XML:

<rdf:RDF xmlns:cim="http://iec.ch/TC57/2012/CIM-schema-cim16#" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
   <cim:SynchronousMachineTimeConstantReactance rdf:ID="_54302da0-b02c-11e3-af35-080027008896">
      <cim:IdentifiedObject.aliasName>GENCLS_DYN</cim:IdentifiedObject.aliasName>
      <cim:IdentifiedObject.name>RoundRotor Dynamics</cim:IdentifiedObject.name>
      <cim:SynchronousMachineTimeConstantReactance.tpdo>0.30000001192092896</cim:SynchronousMachineTimeConstantReactance.tpdo>
      <cim:SynchronousMachineTimeConstantReactance.tppdo>0.15000000596046448</cim:SynchronousMachineTimeConstantReactance.tppdo>
   </cim:SynchronousMachineTimeConstantReactance>
</rdf:RDF>

Which becomes the following TURTLE:

<file:///R:/workspaces/create/git-svn/create-sparql/RDF/XML#_54302da0-b02c-11e3-af35-080027008896>
        a                               cim:SynchronousMachineTimeConstantReactance ;
        cim:IdentifiedObject.aliasName  "GENCLS_DYN" ;
        cim:IdentifiedObject.name       "RoundRotor Dynamics" ;
        cim:SynchronousMachineTimeConstantReactance.tpdo "0.30000001192092896" ;
        cim:SynchronousMachineTimeConstantReactance.tppdo "0.15000000596046448" .

RDF operates at the statement level, so to find out that your _54302da0-b02c-11e3-af35-080027008896 is a cim:SynchronousMachineTimeConstantReactance you would look for the corresponding triples. Jena's Model API (linked to above) will provide you with methods to identify the properties that resources have.

The following will list all statements whose subject is the aforementioned resource:

final Resource s = model.getResource("file:///R:/workspaces/create/git-svn/create-sparql/RDF/XML#_54302da0-b02c-11e3-af35-080027008896");
final ExtendedIterator<Statement> properties = s.listProperties();
while( properties.hasNext() ) {
    System.out.println(properties.next());
}

which produces:

[file:///R:/workspaces/create/git-svn/create-sparql/RDF/XML#_54302da0-b02c-11e3-af35-080027008896, http://iec.ch/TC57/2012/CIM-schema-cim16#SynchronousMachineTimeConstantReactance.tppdo, "0.15000000596046448"]
[file:///R:/workspaces/create/git-svn/create-sparql/RDF/XML#_54302da0-b02c-11e3-af35-080027008896, http://iec.ch/TC57/2012/CIM-schema-cim16#SynchronousMachineTimeConstantReactance.tpdo, "0.30000001192092896"]
[file:///R:/workspaces/create/git-svn/create-sparql/RDF/XML#_54302da0-b02c-11e3-af35-080027008896, http://iec.ch/TC57/2012/CIM-schema-cim16#IdentifiedObject.name, "RoundRotor Dynamics"]
[file:///R:/workspaces/create/git-svn/create-sparql/RDF/XML#_54302da0-b02c-11e3-af35-080027008896, http://iec.ch/TC57/2012/CIM-schema-cim16#IdentifiedObject.aliasName, "GENCLS_DYN"]
[file:///R:/workspaces/create/git-svn/create-sparql/RDF/XML#_54302da0-b02c-11e3-af35-080027008896, http://www.w3.org/1999/02/22-rdf-syntax-ns#type, http://iec.ch/TC57/2012/CIM-schema-cim16#SynchronousMachineTimeConstantReactance]

which produces: