Lecture 24: Data Formats and Encoding

Compact Encodings

So what's the best way to encode compact data?

Answer #1:: Compress the XML before transmission? Wrong. Why? Unless the document is large, typical compresion algorithms (eg gzip) actually make the data bigger. And lots of CPU power is needed at the receiver to decompress. This is a contentious issue, however.
Answer #2:: Ignore the problem. Unfortunately this is wrong too. The problem is that in XML the recipient is required to "parse" (a slightly different meaning of the word than previous) the document to extract information. This can be compared to the traditional RPC approach where the RPC libraries map information directly to "internal" data structures. Parsing is a heavy consumer of CPU, and hence battery power. Note that there isn't universal agreement on this point either.
Answer #3: Invent a standardised way of converting an XML entity into a new (compact) form for transmission. The XML Binary group is working on this possibility.
Answer #4: Use an existing compact binary encoding, of which the best known and understood is probably ASN.1/BER!

Lecture 24: Data Formats and Encoding -- A Philosophy Lecture