The NepomukMiddleware is the way to make sure your service is visible to other NepomukServices. When a service is registered with the middleware it will do three things:

• Make this service accessible through the OSGIServiceTracker
• Attempt to make this services accessible through SOAP, this requires a valid WSDL file, see below. It will fail silently, so if you are not interested in SOAP (and you shouldn't be) just leave the WSDL out)
• Make this service accessible through XMLRPC

For accessing services through the middleware, see NepomukServices

Programming against the OSGI Nepomuk Middleware

Creating the service

• Create a java interface for your service (can be automatic, or the two steps can be reversed)
• Implement your service as a java class
• Use only simple types (String,Integer,Double), Arrays of these, Collections of these, or simple JavaBeans? (See also MiddlewareTypes)
• Add a NepomukType? annotation to your interface (Note that the WSDL pointed to in NepomukType? does not need to exist, it can be generated later if needed):

  @NepomukType(type="http://www.dfki.uni-kl.de/~grimnes/2006/11/nepomuk/ExampleService.wsdl")
  

• OPTIONAL: Add a WebService? annotation to your interface (this is only needed if you want to general WSDL for your service or you want it SOAPified.):

  @WebService(targetNamespace="http://exampleservice.examples.nepomuk.semanticdesktop.org", name="ExampleService")
  

  • If you want a WSDL file - make sure you read CorrectWSDLs to learn about where to put your wsdl file for Nepomuk to cache it for offline work.

Registering

• Do NOT register your service directly with OSGI, instead use the Nepomuk registery:

ServiceReference sr = context.getServiceReference(OSGIRegistry.class.getName());
if (sr==null) { 
  log.fatal("Could not find Nepomuk Registry - aborting.");
  throw new Exception("No Nepomuk registry found");
}
registry=(OSGIRegistry) context.getService(sr);
		
service = new ExampleServiceImpl();
		
registry.registerService(ExampleService.class, service, "ExampleService");

• This will register your service as:
  1. A soap service, accessible under http://localhost:8181/soap/servicename
  2. A OSGI Service, accessible as normal (but dont do this directly! See below)
  3. With the Nepomuk Middleware Registry

Invoking Services

• To discover Nepomuk service of a certain types, use the NepomukServices interface:

  ServiceReference sr = bc.getServiceReference(NepomukServices.class.getName());
  if (sr==null) { 
    log.warn("Could not find NepomukServices - aborting.");
    throw new Exception("No NepomukServices found");
  }
  NepomukServices registry = (NepomukServices) bc.getService(sr);
  		
  ExampleService service = registry.getService(ExampleService.class);
  

Note, this only works when the ExampleService? has a NepomukType? annotation. The NepomukServices interface also has getRdfRepository and a few other utility method for commonly used services.

Debugging

If you have trouble you can go to http://localhost:8181/middleware/index This lists all services registered with the middleware and has links to their XMLRPC/SOAP endpoints as well as a link for generating WSDL for services that has WebService? annotations.

If you are attempting to do SOAP (which I do not recommend), the middleware will be default fail quietly. For verbose SOAP debugging set the property org.semanticdesktop.nepomuk.soap.debug to true in config.ini

Any questions/comments, let Gunnar know!