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Java API

From: McBride, Brian <bwm@hplb.hpl.hp.com>
Date: Fri, 4 Aug 2000 17:34:28 +0100
Message-ID: <5E13A1874524D411A876006008CD059F1006CD@0-mail-1.hpl.hp.com>
To: "RDF Interest (E-mail)" <www-rdf-interest@w3.org>
I have been getting feedback about the current java RDF API from potential
RDF users in HPLabs.  A number of issues with the current API are inhibiting
the adoption of RDF in this organisation.  I have been exploring some ideas
for addressing these issues in the form of an evolution of the SiRPAC API.
I'd appreciate the comments of this group on the results.
 
I am in the process of building an implementation of these enhancements
which I intend to make freely available.    I have got far enough with the
design that I am reasonably confident that it is implementable.   I would
like to get early feedback before getting too far into the implementation.
In particular I'd welcome comments on:

*	is the overall style appealing?
*	preferences for strict evolution from the current SiRPAC API versus
conforming to current java stylistic conventions
*	detailed comments on the interfaces

I'd like to stress that what I am proposing is an evolution of the excellent
work that has already been done on RDF API's.  This evolution has been
motivated by a desire  to address specific concerns raised by potential
users.  I'd also like to acknowledge that I 'borrowed' the core idea from
Dave Beckett at ILRT.
 
The main changes are:

*	whilst maintaining the current statement centric method calls, added
a set of resource centric method calls which are cascadable to make code
easier to read and write
*	explicit container support
*	typed data values in literals - supports built in types and user
defined objects
*	property as an explicit type
	
*	subclassing of resource to provide resource specific behaviour (used
by containers)
*	explicit support for reification (... dare I mention this :)
*	a style more consistent with current java api practice  

Here are some brief code samples:
 
// create the structure in Figure 2 of m&s
 
    Resource ora = model.createResource()
                        .addProperty(Dc.name, "Ora Lassila")
                        .addProperty(Dc.email,  <mailto:lassila@w3.org>
lassila@w3.org);
 
    Resource page = model.createResource(  <http://www.w3.org/Home/Lassila>
http://www.w3.org/Home/Lassila)
                         .addProperty(Dc.creator, ora);
 
 
The alternative in the current API (as I have implemented it) might be:
 
    Resource ora = model.createResource();
    model.add(model.createStatement(ora, DC.name, "Ora Lassila"));
    model.add(model.createStatement(ora, DC.email, lassila@w3.org
<mailto:lassila@w3.org> ));
    Resource page = model.createResource();
    model.add(model.createStatement(page, DC.creator, ora);
 
// create bag structure from figure 4 of m&s
 
    Resource bag = model.createBag() 
                        .addResource("/Students/Amy")
                        .addResource("/Students/Tim")
                        .addResource("/Students/John")
                        .addResource("/Students/Mary")
                        .addResource("/Students/Sue");
    Resource course = model.createResource("/courses/6.001")
                           .addProperty(Myschema.students, bag);
 
Again the alternative:
 
    Resource student = null;
    Resource course = model.createResource("/courses/6.001");
    Resource bag    = model.createResource();
    model.add(model.createStatement(bag, RDF.type, RDF.Bag));
    model.add(model.createStatement(course, MYSCHEMA.students, bag));
    student = model.createResource("/Students/Amy");    
    model.add(model.createStatement(bag, RDF.li(1), student));
    student = model.createResource("/Students/Tim"); 
    model.add(model.createStatement(bag, RDF.li(2), student));
    student = model.createResource("/Students/John"));
    model.add(model.createStatement(bag, RDF.li(3), student));    
    student = model.createResource("/Students/Mary"); 
    model.add(model.createStatement(bag, RDF.li(4), student));    
    student = model.createResource("/Students/Sue"); 
    model.add(model.createStatement(bag, RDF.li(5), student));             
 
// access the i'th element of the bag starting from course
 
   Resource student = course.getProperty(Myschema.students)
                            .getProperty(Rdf.li(i)).getResource();
 
Again the alternative
 
    Model m = model.find(course, MYSCHEMA.students, null)
    Statement s = (Statement) m.elements.next();
    m = model.find(s.subject(), RDF.li(i), null);
    s = (Statement) m.elements.next());
    Resource student = (Resource) s.object();
 
// a reification from figure 8 of m&s
 
    Resource page = model.createResource("http://www.w3.org/Home/Lassila")
    Model.createStatement(page, Dc.creator, "Ora Lassila")
         .addProperty(SomeSchema.attributedTo, "Ralph Swick");
 
// creating and accessing a compound value from figure 15 of m&s
 
   john.addProperty(Nschema.weight, model.createResource()
                                         .addProperty(Rdf.value, 200)
                                         .addProperty(Nschema.units.
Nschema.Pounds));
   int weight = john.getProperty(Nschema.weight)
                    .getProperty(Rdf.value).getInt();
 
// transactions (if supported) are also inline
 
    Resource bag = model.begin()
                        .createBag() 
                        .addResource("/Students/Amy")
                        .addResource("/Students/Tim")
                        .addResource("/Students/John")
                        .addResource("/Students/Mary")
                        .addResource("/Students/Sue")
                        .commit();
 
//  there are two kinds of query operation - one group returns iterators on
the
//  the current model, the other group, as with the original returns, a new
model.
 
//  return an iterator over all bags in the model
 
    ResIterator iter = model.listSubjectsWithPredicate(Rdf.type, Rdf.Bag);
 
// return all the creators in a model
 
    ResIterator iter = model.listObjectsOfPredicate(Dc.creator);
 
   
 
 
That should be enough to give a flavour.  The current (work in progress)
interface files are attached.
 
Brian McBride
HPLabs
 
 
 
   
 
 
 



Received on Friday, 4 August 2000 12:34:46 GMT

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