Re: 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