Re: Distributed programming in heterogeneous platforms

[Jim Rogers <jimmaureenrogers@worldnet.att.net>]

Robert C. Leif wrote:

> What would happen if the Ada Distributed Systems Annex were used with
> XML messages that were validated by both the sender and receiver with
> the same XML schema?
> Bob Leif 
> 


Clean but painfully slow data communication would be achieved.
XML forces all data to be encoded as strings. There is also a significant
overhead in XML tags being passed with the data. This allows strong
platform independence, but is very inefficient.

For most applications the inefficiencies are not important. The latency
accessing a local or remote database may be orders of magnitude greater
than the XML coding/decoding inefficiencies. For hard real time command
and control systems the overhead of XML can be unbearable. In the robotics
program I mentioned earlier we could not even bear the overhead of full
IP protocol. We needed to send all our data at lower levels in the OSI
stack. We were given a very narrow RF bandwidth and a maximum transmission
rate of 24000 baud, with expected average transmission rates closer to
19.2K baud. In our situation XML would have been unacceptable.

Jim Rogers