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W3C launches Binary XML Packaging
Spy der Mann writes "Remember the recent discussion on Binary XML? Well, there's news. The W3C just released the specs for XML-binary optimized packaging (XOP). In summary, they take binary data out of the XML, and put it in a separate section using MIME-Multipart. You can read the press release and the testimonials from MS, IBM and BEA."
Unless I'm horribly misreading the specification, it appears to be a way to package up XML documents and binary data that they reference into a neat package with MIME - not a way to convert a (text) XML document into a binary one.
Ummm...it's "OK". This is probably the least ambitious Binary XML spec imaginable. That may actually be good, but I don't know. Lets see what's up here...
First of all, it's completely impossible to stream this format. All the binary chunks have to be read at some point in the future when the actual XML non-opaque content is complete. In a stream, that never happens. (Of course, XML isn't the most stream friendly protocol...you can't validate a stream.)
Secondly, this isn't wonderful for large files either; you're constantly seeking for binary data that can be many megabytes away. We solve this in web pages by having the images be completely separate (binary) files.
Thirdly, its telling that they used a PNG as a data type. Besides being yet another file format that needs its own custom binary parser (heh, I like PNG, I'm just complaining about it in the XML whinespace), it's big and simple and there's just one there. One of the things I really liked about the various Binary XML formats was the degree to which they expressly typed things like arrays of floating point values or little-endian integers. Converting values between binary and string format is an enormously painful process, one that frankly I'm astonished hasn't received CPU acceleration at this point. Every other Binary XML format has seriously thought about how to efficiently but correctly manage large arrays of such values. XOP just says...heh...you wanna dump alot of data efficiently? Check your typing at the door. Feel free to bring a buffer-overflow ridden parser in with you if you like, though.
Don't get me wrong, there's a fundamental simplicity to XOP that I can certainly understand how it's appealing. But it seems to go so massively against what XML represents that I'm not entirely sure XOP encoded content deserves to be compliant with the very regulations that forced XML adoption in the first place: Opaque formats are too expensive to maintain for any amount of time, therefore either self-describe or don't get deployed. A self-decribing document that says "All performance-critical content is opaque" seems rather counter to this spirit.