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From John Wilson <...@wilson.co.uk>
Subject Re: Mobile devices..
Date Sun, 11 Jan 2004 15:35:01 GMT

On 11 Jan 2004, at 14:21, Danny Angus wrote:

> Hi,
>
> First of all, thanks for xmlrpc, we've recently finished a public 
> demonstration of a client-server application where the clients are 
> mobile devices (phones, PDA's etc).
>
> The server serves a map and publicly authored content associated with 
> points on the map.
>
> The idea is that as you navigate the city you can leave (author) 
> content as you go, and read/view things other people have authored.
> For fuller details of our project see this: 
> http://www.proboscis.org.uk/urbantapestries/index.html

Look cool!!
>
> ATM it is pretty much being held back by the lack of network coverage 
> and the poor resolution of location awareness, but it was a research 
> project not commercial software, and proved the concept to the 
> satisfaction of our funders.
>
> So to my point...
> We used XMLRPC to give us ready made RPC functionality across a broad 
> range of client platforms and I'd already used it in another project 
> so I knew what to expect.
>
> The issue we have encountered is that not only is the XML quite big 
> for our limted bandwidth use-case, but parsing it is also quite 
> involved for a limited capability device.


You are using Apache XML-RPC client with MinML?

Is you problem speed or memory footprint?
>

> I've seen discussions of zip'ing the xml to cut down on bandwidth, 
> which will might possibly help (or just offload the bottleneck to the 
> device again!), is there any similar action which could be taken to 
> reduce the XML parsing effort, a simpler schema that could be used 
> perhaps?


It's certainly possible to reduce the number of tags used in the 
message (you don't generally need <value> or <param>) but then you 
would lose the interoperability benefits of XML-RPC.
>
> We deliberately restrict ourselves to only using String's for values 
> throughout, but make much use of structs and arrays.
>
> Have any other users encountered these (or similar) issues, and what, 
> if any, solutions could you share with us?
>

I'm a member of the JSR 172 expert group 
(http://www.jcp.org/en/jsr/detail?id=172) and we looked long and hard 
at the problems of using SOAP on mobile devices. None of the device 
vendors would consider using non standard approaches to reducing 
bandwidth (i.e. a big no to 'binary xml') - they got burned by WAP and 
weren't going that way again. Zipping the data stream is OK, it works 
very well with XML but it is memory and computationally expensive.

I wrote MinML-RPC (see my web site) as an XML-RPC implementation for 
embedded devices with far less resource than the ones you are using. 
It's a server only implementation at the moment but there's not a lot 
of difference between processing an XML-RPC request and a response so 
it's hackable ro a client.



John Wilson
The Wilson Partnership
http://www.wilson.co.uk


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