Re: SWI-Prolog engine as a Service

Pavan, Sergio,

On 04/22/2014 11:56 PM, Sergio Castro wrote:
> If your client is a Java program and you can execute it in the same
> machine than SWI, I think the best you can do is to try with JPL.
> Configuring it as a web service in that scenario may add another
> layer of complexity. Also you would experiment a strong impact on
> performance.

Yes and no.  As you have experienced, JPL is not without problems.  On Unix
systems Prolog tends to fight over signals with Java (both needs signals
for similar thread communication requirements), causing several
stability problems depending on what you are doing and which JVM you are
using.  These problems are very hard to diagnose and it is unclear whether
or not they can be fixed.  Certainly not in a proper JVM-independent way.
On all platform, merging Prolog and Java suffers from configuration issues.
Most have to do with wrong paths and merging different architectures (e.g.,
32 and 64-bit).  They require proper knowledge of dynamic linking and
dynamic linking debugging tools to fix.  It is hard to provide recipes
because there are just too many combinations of OS, Prolog and JVM.

Using Prolog as a (web-) service, talking through sockets avoids all this.
You get socket communication overhead in return.  If you use direct sockets,
that should be well below 1ms.  If you use HTTP it becomes easier, be the
price you pay is `a few ms'.  The other advantage is that you have natural
access to the Prolog toplevel, which makes it easier to debug your program.

I don't see the problem of `starting Prolog as a service': just start Prolog
and use the http HOWTO/Tutorial to provide the service.  You can start
Prolog
by hand separately, or make the Java program fire Prolog.

	Cheers --- Jan


>
> Sergio
>
>
> Le Mardi 22 avril 2014 17h26, Pavan Kumar <[email protected]> a écrit :
>
> I have a Java Program that will generate a Query for SWI-Prolog(CLPFD). I
>> need this query to be sent to SWI-Prolog for further processing and getting
>> back the results or Output of the SWI-Prolog.
>>
>> I figured out JPL is a good approach and also we can try to host SWI-Prolog
>> engine as a Web Service and send our query which is generated by Java
>> Program to get back the results.
>>
>> I saw a web services section in SWI-Prolog Documentation but it seems like
>> creating web Servers in SWI-Prolog which serves html pages and http
>> requests but not the SWI-Prolog Functionality as a Service itself.
>>
>> Can you let me know which is the better approach for my problem? JPL or
>> Hosting SWI-Prolog engine as a service?
>>
>> If the latter is better can you guide me how to do it and communicate with
>> the web service?
>>
>> I am using a Windows 8 machine with SWI-Prolog 6.6.4 setup.
>>
>> Thanks,
>> Pavan.
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