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From Supriyo Chatterjea <supriyo_chatter...@yahoo.com.sg>
Subject Re: Web services on a wireless adhoc network
Date Thu, 11 Jul 2002 07:55:21 GMT
Well I've dropped the idea of using a UDDI sort of
registry to store all the service descriptions, etc.

So this is what I'm thinking of doing now:

1. I'm thinking of using an XML Java parser (Xerces2)
to scan the WSDL file at the service provider and find
the <service> tag. Once I get that, I should be able
to retrieve other stuff like names and port bindings.

2. Next step would be to use the names, port bindings,
a TLL for the service, etc to generate another XML
file that would be something like a registry for that
service provider.

3. Service requesters can access this newly generated
XML file to see what services are available.

Any comments on this model? Do you think Xerces2 is
suitable for an embedded device or are there some
other more lightweight XML parsers out there which are
capable of running on Java and both reading and
writing XML files?

One more question about the service description
format. I'm thinking of having a hierarchical
structure to the service description, for example:

1. Output device
1.1 Printer
1.1.1 Laser Printer
1.1.2 Inkjet printer

1.2 Screen
1.2.1 CRT
1.2.2 LCD

2. Information
2.1 Weather
2.2 Currency Converter

and so on....

So I plan to put this categorisation information in
the WSDL file. Which tag should I put it under? The
<service> tag? How exactly do I go about making such
user-defined definitions?

Thanks,
Supriyo

--- Steve Loughran <steve_l@iseran.com> wrote:
> 
> makes sense to me.
> 
> What you want is dynamic lan scoped service
> discovery, rather than
> centralised registries for internet scope binding.
> 
> I have been prototyping something to do this in my
> limited spare time; a
> multicast IP based system with
> 
> -a variant of SLP for locating services. It will use
> XML, though at the
> current stage I just serialize a java object
> -an add in to axis that serves up all registered
> soap services on the
> webapp.
> -a client to find services by name
> 
> There is no central registry at all; things just ask
> for all implementations
> of service:foo and get back a list of URLs; if they
> set the time to live of
> the packet they can ask the lan or the site. If you
> ask 5 minutes later, you
> get back a different list.
> 
> I will stick this in the proposal corner of axis in
> a week or two, under the
> name of 'mir': multicast endpoint resolution. I want
> to get up to using XML
> payloads in the datagrams first; serialized objects
> are quick and dirty for
> prototyping but too unstable/unportable.
> 
> -steve
> 
> ----- Original Message -----
> From: "Supriyo Chatterjea"
> <supriyo_chatterjea@yahoo.com.sg>
> To: <axis-user@xml.apache.org>
> Sent: Tuesday, July 09, 2002 9:44 AM
> Subject: Web services on a wireless adhoc network
> 
> 
> > Hi,
> >
> > I'm trying to implement web services on a wireless
> > adhoc network. I've given a brief overview of the
> > problem and the tools I'm planning to use and
> that's
> > followed by a couple of questions.
> >
> > Consider a few wireless devices within range of
> each
> > other each providing its own service(s). Each
> device
> > maintains a sort of registry that keeps track of
> all
> > the services that are being offered by all the
> devices
> > in the adhoc network at a certain instant, e.g. if
> a
> > network consists of devices A, B, C and D, device
> A's
> > registry lists the services provided by itself
> *and*
> > the services of devices B, C and D.
> >
> > If a new device E enters the network, a service
> > discovery algorithm ensures that A, B, C, D and E
> all
> > have their own registries updated to indicate the
> > services offered by all the devices in the adhoc
> > network.
> 
> it is not clear you need to do this; the rate of
> change in a dynamic WLAN
> means that you might as well ask for services on
> demand.
> 
> >
> > So basically,
> >
> > (i) every device acts as a service provider *and*
> a
> > service requester (client & server)
> 
> OK
> 
> >
> > (ii) every device has it's own private registry
> that
> > lists its own services *and* the services of the
> other
> > devices in the network
> 
> not needed
> 
> 
> > Another point is that these services aren't
> exactly
> > services being offered by businesses. It could
> apply
> > to the following scenario, e.g. you receive an
> email
> > on your PDA and would like to print it out.
> However,
> > there isn't any printer available. Some time
> later,
> > you happen to walk into a room where a printer is
> > available. Your PDA detects the printer and asks
> you
> > if you would like to print out your email.
> 
> not a problem.
> 
> 
> > So I'm talking about services like printing,
> > displaying some output on a screen, etc., not
> services
> > offered by businesses. And by the way these
> devices
> > are embedded devices.
> >
> > Now I'm thinking of using Jakarta Tomcat for the
> web
> > server and Apache Axis for the SOAP engine.
> >
> > Do you think that's an ok choice?
> 
> 
> The alternative is Jini, which was designed for this
> kind of thing.
> 
> >
> > Does anyone have any idea how I should go about
> > implementing the registry?
> 
> like I said, what registry? Use multicast or
> broadcast discovery and you
> dont need the central registry
> 
> 


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