[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: ASN.1 is an XML Schema Language (How many encodings?)
Claude L Bullard wrote: > given your years of experience, why are multiple > encodings ever necessary excepting the binary which > I put in a class of its own? Frankly, I think it is usually very hard to justify anything more than one textual encoding and one binary encoding. Typically, the textual encoding will be big, fat and full of compiler sugar that makes it easy for humans to read. On the other hand, the binary encoding should be as tight and fast to decode as possible for whatever the underlying data type is. Other than that, the only reason I can see for having more than two encodings would be to produced encodings that are useful for signing. (i.e. like the CXER and DER encodings). But, these "signable" encodings are usually best, and most easily defined as profiles on more general encodings. You might also have a need for variablity in your human readable encoding to handle I18N (i.e. French folk don't like seeing thing like "street" or "zip code" in an address record...) I18N also leads to all sorts of "virtual" encodings in order to handle different character sets. (Like the many versions of XML that differ only in character set.) Typically, other than the two encodings (one for humans, one for machines) discussed above, and ignoring the I18N-driven need for variety in the textual encodings, the need for additional encodings is usually just to respond to the damage done by idiots who have inflicted upon the market some new encoding that contributes little but still must be supported due to market acceptance. Sometimes they do this because they are ignorant of what already exists. Sometimes it is because they have a personal aesthetic preference for one style of encoding over another, and sometimes it is because they intentionally want to create a new encoding so that they can get some "proprietary advantage" from using it. The reasons don't matter. Once a large number of customers demand support for some stupid format-of-the-week, you have little choice but to support it. Whatever the case, I think you'll typically see much more *need* for variety in textual encodings rather than in the binary encodings. But, to answer your original question, I think that many of the alternative encodings are simply unnecessary. But, it turns out that the effort needed to support two encodings is pretty much the same effort needed to support any number greater than one. Thus, it makes sense to go the tiny extra step and provide support for any number while doing one's best to ensure that there are really only two.... bob wyman
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