Efficient XML Interchange High Performance XML Don McGregor (mcgredo (at) nps.edu) Don Brutzman (brutzman (at) nps.edu)

W3C EXI Working Group Chartered by the World Wide Web Consortium Tasked to Develop a specification for an encoding format that allows efficient interchange of the XML Information Set, and Illustrate effective processor implementations of that encoding

XML Virtues XML has become the default format for the storage and interchange of information It has many virtues: simple, human readable, flexible, and a huge array of tools to support transformation, storage, reading, indexing, etc. Like any standard, it becomes more valuable as more things use it. This dynamic has driven its use to places not previously considered XML domains

Newer XML Applications Network protocols High speed web services Low power devices (cell phones, sensor networks, etc) Archiving large data sets DoD tactical messaging systems

XML Vices XML is also Verbose & bandwidth intensive Text-based; converting to binary is expensive (databinding) Parsers can consume significant power; batteries are not on the same improvement curve as CPUs

XML Vices: Bandwidth Text takes bandwidth Tags ( ) are a significant portion of the overall document size Gzip of XML documents is not always enough; we can get better compactness, and there are interactions with other issues Size is a major issue in tactical links

XML Vices: Databinding Databinding ties text XML to (usually) programming language objects Needs to be tied to something like a Java object public class Point { float x, y, z; } This involves parsing the text, converting to binary, and stuffing it into the object It’s a lot more efficient to simply send binary (though you need to be careful about endian issues)

XML Vices: Power Consumption XML is migrating to phones, sensor networks, etc. Batteries are on a slow improvement curve; a full XML parser can be somewhat expensive in terms of power. Doing gzip to get compactness adds to the power budget

Efficient XML This has led the W3C to create an Efficient XML Interchange (EXI) working group to agree on a standard, rather than continue to use multiple incompatible formats EXI is an alternative representation of XML that is more compact, faster to parse, consumes less power, and has better data binding characteristics It accomplishes this by giving up the text-based, human-readable representation in favor of a binary format It’s still XML--just a different representation of the same information

EXI Replace text tags (,, etc) with a shorter binary representation For schemas-described documents, we can use the information to handle numeric fields as binary values The resulting document compresses better than the original text document Better data binding than classic XML or gzipped XML. If you run the EXI through gzip, you’ll also get a smaller file than the original gzip’d XML Lower power consumption to parse

EXI Status Public working draft of specification published; probably go to “final call” in early Final call is the point at which it receives most of the outside scrutiny One commercial implementation (subject to specification changes) Open source Java implementation being worked on by Sun, Fujitsu, Siemens, NPS Lower power J2ME implementation is possible down the road

EXI DoD should adopt a standard, not a product. EXI is just another format for XML. If you want to go back to XML, or even go to another binary XML standard, simply convert back to XML XML Infoset Text XML Format EXI Format

Applications:Messaging Military messaging: conventional XML is 10-20X larger than existing binary message formats Bandwidth is limited and heavily in demand for other applications Bespoke message formats are brittle and not easily handled by other applications EXI can be ~10-30% larger than custom binary formats (depending on application)

Applications: Low Power Cell phone/PDA integration with military formats

Applications: Chat Chat/IM is playing a bigger role in the military XMPP is an XML based chat application adopted as a standard by DoD Chat messages are XML based, but go over military TCP/IP channels, which have limited bandwidth Should be possible to replace the existing XML streams with EXI streams

Applications: X3D X3D is an XML-based standard for 3d scenegraphs File sizes can get large; there’s a lot of information to represent in a 3D scene We may need to transfer this across networks (as in X3D-Earth)

EXI The benefits of XML: easily transcoded to conventional XML format, access to the vast XML toolset Alleviates some of XML’s problems by giving up human-readable text We gain compactness, databinding, fast parsing speed, and low power