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== A Prototype Implementation for Decentralized Reasoning ==

<<TableOfContents(3)>>
 
Our implementation is a customized version of the '''OWL API''' so as to support distributed reasoning tasks. 
It is based on the traditional client-server paradigm, and makes it possible for a semantic web application to connect to a remote reasoning server over TCP/IP, acting as a middleware. 

 * It includes the following components: 

  * A client application.
  * A server application.
  * Some customized files, altered variants of the original OWL API's ones. 

 * It requires a functional OWL API installation. 

 * It is '''open source''' and available under the '''LGPL License'''. 


=== Client Application ===

Client application consists of two files: {{{myReasoner.java}}} and {{{FunctionsDefineIndex.java}}}.

{{{myReasoner.java}}} contains {{{myReasoner}}} class, which has two constructors. The first constructor has three arguments: an {{{OWLOntologyManager}}} object {{{(OWLOntologyManager manager)}}}, a {{{String}}} object that defines the server's IP address {{{(String address)}}}, and an {{{int}}} variable for the port that the server listens to {{{(int port)}}}. 

{{{FunctionsDefineIndex.java}}} has two arguments {{{(OWLOntologyManager manager, String address)}}} and uses the default value for the port (13000).

Thus, an original OWL API application just needs to import myReasoner.java and create a {{{myReasoner}}} object:

{{{#!java numbers=disable
myReasoner reasoner = new myReasoner(manager, address, port);
}}}

From now on any method can be used like in the original OWL-API (i.e. reasoner.<method_name>), for example: 

{{{#!java numbers=disable
reasoner.classify();
}}}

{{{FunctionDefineIndex.java}}} contains {{{FunctionDefineIndex}}} interface, that defines a unique identifier {{{(int)}}} for each method, in order to standardize client-server communication. 


=== Server Application ===

Server application consists of three files: {{{SingleThreadedServer.java}}}, {{{SingleThreadedServerMain.java}}} and {{{FunctionDefineIndex.java}}}. 

{{{SingleThreadedServerMain.java}}} contains the main functions of the server application.

{{{SingleThreadedServer.java}}} contains {{{SingleThreadedServer}}} class, which has two constructors. The first constructor has one argument {{{(int port)}}}, the port that the server listens to. The second one (default constructor) has no arguments, and uses the default value for the port (13000).

In the '''multi-threaded version''' of the server application, there is one more file, {{{WorkerRunnable.java}}}, in order to support multiple threads.

=== Additional Files ===

In our implementation, we tried not to make any severe changes in the original OWL API code, but it wasn't an easy task.

One problem was that, for object serialization to be used, we had to support Java Serialization Protocol. In order to avoid adding ''{{{implements Serializable}}}'' to all OWL API's classes and interfaces, we preferred to add ''{{{extends Serializable}}}'' to the definition of {{{OWLObject}}} interface, which is being inherited by almost all OWL API's classes and interfaces, except for some inner classes of {{{OWLOntologyImpl}}} class. These classes implement the interfaces: {{{OWLOntologyChangeVisitor, OWLEntityVisitor and OWLAxiomVisitor}}}. Thus, we added {{{extends Serializable}}} to all the three of them.

A second problem was that Java Serialization protocol can't byte-transform any static class variables, as found in {{{AxiomType.java}}} and {{{OWLOntologyImpl.java}}} files. In these files we had to change a bit the original OWL API's source code.

So, in order for our application to function, one has to overwrite the original {{{OWLObject.java, AxiomType.java, OWLOntologyChangeVisitor.java, OWLEntityVisitor.java}}} and {{{OWLAxiomVisitor.java}}} files (in OWL API's {{{org.semanticweb.owl.model}}} package), as well as {{{OWLOntologyImpl.java}}} file (in OWL API's {{{uk.ac.manchester.cs.owl}}} package) with our custom ones.

{{{#!wiki note
In some cases we observed some problems with our server application, because of Java Serialization protocol's inefficient handling of large amount of serialized objects (1000+). In such a case we strongly recommend to increase server's '''heap memory''' (at least 1024 MB).
}}}

=== Download and Instructions ===

The source code of our implementation is available through the following links, as per implementation part: [[attachment:Client.zip|Client implementation]], [[attachment:Server.zip|Server implementation]] and [[attachment:custom_files.zip|custom files]]. An application also needs to import the corresponding libraries of the original OWL API (currently, v. 2 is supported), which is available for download through [[http://sourceforge.net/projects/owlapi/files/|SourceForge]].