How Can Individual Bits of a Word Be defined In XML?

[benn]

I have a microcontroller that I wish to send status data (via serial
RS-232) out to a PC com port. Im trying to minimize the amount of
bytes I transmit, so I want the micro to bit-pack various different
fields into just a few bytes.

For example, one 8-bit byte will contain the following information:

Bit 0: Has Green Eyes
Bit 1: Has Brown Hair
Bit 2: Is Under 6 ft
...
Bit 7: Has Freckles


How can I efficiently use XML to tag each bit field?

Thanks!

 

[Joseph Kesselman]

I'm not sure what you're asking. If you want to simply build a map from
the bits to strings describing them, that's easy enough to express in
XML (it's just a table, after all).

But if you want to convert to and from the binary form, you need an
actual programming language. If you've got a microcontroller, the right
answer is generally assembler or something as near to that as possible,
for efficiency's sake.

XML is a good interchange format for data, but is rarely the ideal
format for specific tasks. Could you clarify why you think XML would be
useful in this application?

 

[benn]

I'm not sure what you're asking. If you want to simply build a map from
the bits to strings describing them, that's easy enough to express in
XML (it's just a table, after all).

But if you want to convert to and from the binary form, you need an
actual programming language. If you've got a microcontroller, the right
answer is generally assembler or something as near to that as possible,
for efficiency's sake.

XML is a good interchange format for data, but is rarely the ideal
format for specific tasks. Could you clarify why you think XML would be
useful in this application?

I know next to nothing about XML so this may not make sense at all or
be totally inaccurate.

On the micro side, I can currently send raw serial binary (or ascii)
data and display it on the pc via hyperterminal etc, however, I'd like
to send the data in XML format so that it can be displayed
intelligently on the PC side.
I'm thinking XML might be a good format since the PC will always be
able to display it properly even if I change the organization of the
data bits/fields in the future.

Does this make sense? Could I send this bit-packed binary data (non-
ascii) but with (ascii?) xml tags that tell the pc application about
how the binary data is structured?

Thanks!

 

[Joseph Kesselman]

Does this make sense? Could I send this bit-packed binary data (non-
ascii) but with (ascii?) xml tags that tell the pc application about
how the binary data is structured?

XML isn't magic. It's just portable syntax upon which languages can be
built.

Yes, you could invent a markup language which describes the content of a
block of binary data. Of course you'd then need an application on the
recieving end which understands that description and uses it to access
that data. Search the web for "XML data binding" for descriptions of how
people have associated arbitrary data with XML structure in the past.

XML itself can not contain arbitrary binary data directly -- some
characters have special meaning, some (eg line breaks) are specially
processed, and some (depending on the version of XML) are simply
forbidden. If you wanted to embed the binary data in the XML document,
the usual solution is to do a base-64 encoding (same solution used in
MIME attachments to SMTP mail).

But... If you're going to go to all that work, you may be defeating most
of the advantages of having the data be bit-packed in the first place;
you're adding nontrivial amounts of overhead. If you want to send
unpacking instructions, I'd recommend sending them and the binary block
as separate transfers. Or, quite possibly, giving up on binary and
simply sending an XML-formatted text document which expresses the
information.

XML is not "intelligent data", despite some early hype. It's just data
that's structured so it can be processed intelligently. Someone still
needs to provide the intelligence to create it, understand it, and do
something with it.

 

[benn]

XML isn't magic. It's just portable syntax upon which languages can be
built.

Yes, you could invent a markup language which describes the content of a
block of binary data. Of course you'd then need an application on the
recieving end which understands that description and uses it to access
that data. Search the web for "XML data binding" for descriptions of how
people have associated arbitrary data with XML structure in the past.

XML itself can not contain arbitrary binary data directly -- some
characters have special meaning, some (eg line breaks) are specially
processed, and some (depending on the version of XML) are simply
forbidden. If you wanted to embed the binary data in the XML document,
the usual solution is to do a base-64 encoding (same solution used in
MIME attachments to SMTP mail).

But... If you're going to go to all that work, you may be defeating most
of the advantages of having the data be bit-packed in the first place;
you're adding nontrivial amounts of overhead. If you want to send
unpacking instructions, I'd recommend sending them and the binary block
as separate transfers. Or, quite possibly, giving up on binary and
simply sending an XML-formatted text document which expresses the
information.

XML is not "intelligent data", despite some early hype. It's just data
that's structured so it can be processed intelligently. Someone still
needs to provide the intelligence to create it, understand it, and do
something with it.

Thanks, Im surprised xml does not support raw binary data.. perhaps
xml 2.0 someday!
I think, like you said, the way to go is to un-pack the binary data,
represent each element in ascii, and then transmit it out with the xml
tags around each of those elements. Just curious, do you happen to
recommend any particular book / video on xml?

 

[Joseph Kesselman]

recommend any particular book / video on xml?

http://www.ibm.com/xml -- lots of useful information from basic
tutorials through examples through opinion pieces. (Not all of which IBM
officially agrees with; they're edited as an almost-independent web
journal.)