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Microsoft Releases Office Binary Formats
Microsoft has released documentation on their Office binary formats. Before jumping up and down gleefully, those working on related open source efforts, such as OpenOffice, might want to take a very close look at Microsoft's Open Specification Promise to see if it seems to cover those working on GPL software; some believe it doesn't. stm2 points us to some good advice from Joel Spolsky to programmers tempted to dig into the spec and create an Excel competitor over a weekend that reads and writes these formats: find an easier way. Joel provides some workarounds that render it possible to make use of these binary files. "[A] normal programmer would conclude that Office's binary file formats: are deliberately obfuscated; are the product of a demented Borg mind; were created by insanely bad programmers; and are impossible to read or create correctly. You'd be wrong on all four counts."
Basically, Microsoft reserves the right to sue you for software patent infringements. So do thousands of other big software companies and patent troll outfits. The new thing now is that Microsoft likes to generate FUD by producing partial waivers and promises that apply to some people in limited circumstances (Novell customers, people 'implementing a Covered Specification', and so on). The inadequacy of this promise draws attention to the implicit threat to tie you up in swpat lawsuits, which was always there - but until this masterstroke of PR the threat wasn't commented on much.
Ignore the vague language and develop software as you always have.
-- Ed Avis ed@membled.com
Here's my suggestion: someone should use these specs to create a BSD-licensed implementation as a library. Then, of course, (L)GPL programs would be free to use the implementation. Nobody gets sued, everybody is happy.
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I've worked on some of these file formats quite a bit (I was the text conversion guy when WP went to Corel -- don't blame me, it was legacy code! ;-) ) Anyway, while the formats are quite strange in places, they aren't really that difficult to parse. I would be willing to speculate that this was never really much of a problem in writing filters for apps (or at least shouldn't have been).
;-) But that was a long time ago...
No, the difficulty with writing a filter for these file formats is that you have no freaking clue what the *formatter* does with the data once it gets it. I'm pretty sure even Microsoft doesn't have an exact picture of that. Hell, I barely ever understood what the WP formatter was doing half the time (and I had source code). File formats are only a small part of the battle. You have all this text that's tagged up, but no idea what the application is *actually* doing with it. There are so many caveats and strange conditions that you just can't possibly write something to read the file and get it right every time.
In all honesty I have at least a little bit of sympathy for MS WRT OOXML. Their formatter (well, every formatter for every word processor I've ever seen) is so weird and flakey that they probably *can't* simply convert over to ODF and have the files work in a backwards compatible way. And lets face it, they've done the non-compatible thing before and they got flamed to hell for it. I honestly believe that (at some point) OOXML was intended to be an honest accounting of what they wanted to have happen when you read in the file. That's why it's so crazy. You'd have to basically rewrite the Word formatter to read the file in properly. If I had to guess, I'd say that snowballs in hell have a better chance...
I *never* had specs for the word file format (actually, I did, but I didn't look at them because they contained a clause saying that if I looked at them I had to agree not to write a file conversion tool). I had some notes that my predecessor wrote down and a bit of a guided tour of how it worked overall. The rest was just trial and error. Believe it or not, occasionally MS would send up bug reports if we broke our export filter (it was important to them for WP to export word because most of the legal world uses WP). But it really wasn't difficult to figure out the format. Trying to understand how to get the WP formatter (also flakey and weird) to do the same things that the Word formatter was doing.... Mostly impossible.
And that's the thing. You really need a language that describes how to take semantic tags and translate them to visual representation. And you need to be able to interact with that visual representation and refer it back to the semantic tags. A file format isn't enough. I need the glue in between -- and in most (all?) word processors that's the formatter. And formatters are generally written in a completely adhoc way. Write a standard for the *formatter* (or better yet a formatting language) and I can translate your document for you.
The trick is to do it in both directions too. Things like Postscript and PDF are great. They are *easy* to write formatters for. But it's impossible (in the general case) to take the document and put it back into the word processor (i.e. the semantic tags that generated the page layout need to be preserved in the layout description). That also has to be described.
Ah... I'm rambling. But maybe someone will see this and finally write something that will work properly. At Corel, my friend was put on the project to do just that 5 times... got cancelled each time
While I was a contractor for a now defunct contracting company, we did a contract for Microsoft. This was pre windows 3.1. We did some innovations which I think became the bases for some of the OLE stuff, but I digress, Microsoft had a spec for its "Chunky File Format."
The office format based on the chunky file format does not have a format, per se' It is more similar to the old TIFF format. You can put almost anything in it, and the "things" that you put in it pretty much define how they are stored. So, for each object type that is saved in the file, there is a call out that says what it is, and a DLL is used to actually read it.
It is possible for multiple groups within Microsoft to store data elements in the format without knowledge of how it is stored ever crossing groups or being "documented" outside the comments and structures in the source code that reads it.
This is not an "interchange" format like ODF, it is a binary application working format that happens to get saved and enough people use it that it has become a standard. (With all blame resting squarely on M$ shoulders.)
It is a great file format for a lot of things and does the job intended. Unfortunately it isn't intended to be fully documented. It is like a file system format like EXT2 or JFS. Sure, you can define precisely how data is stored in the file system, but it is virtually impossible to document all the data types that can be stored in it.