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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: ASN.1 is an XML Schema Language (Fix those lists!) and Bin
 Tim Bray wrote: > [Internet is] an existence proof that syntax is *a* good > basis for interoperation. A focus on concrete syntax may have been good enough to get us to where we are, but that doesn't mean it is the best approach or even the only good approach. > I think it is actually a win, in networked environments, > to decouple the sender's and receiver's data models. Sure, but we shouldn't decouple the implementor's understanding of the abstract data model from the protocol designer's understanding of it. The ASN.1 approach of designing with abstract syntax and then using deterministic translations to concrete syntax greatly improves the effectiveness with which a protocol can be communicated. The result should be higher interoperability. > the notion that there's no re-use between protocols in the > Web/concrete approach is just silly; HTTP is As I'm sure you realize, I was refering to things like Telnet, FTP, SMTP, SNMP, NNTP, etc. which have completely divergent code bases above the TCP/IP layer. The history of protocol development is made up of these isolated efforts and it was this history that your original mailing seemed to be refering to. Reuse of protocol components on the Internet has been a rare and primarily recent phenomenon. (With some exceptions -- notably OSI efforts in ancient history and some recent examples in the Web world.) > it is a defining characteristic of Web Architecture that > interactions are defined at the level of syntax, and for > the needs of the Web, this works well and should be respected. Are you saying that just because it has worked in the past we shouldn't try to do better? In any case, an argument for ASN.1 is not an argument against concrete syntax. Remember, the concrete syntax for something defined in ASN.1 is deterministically generated. That means that you can view ASN.1 as simply a complex form of BNF. You *do not* lose the benefits of agreement on concrete syntax by moving to specification via abstract syntax as long as you keep deterministic generation of concrete syntax. What you lose is the opportunity to introduce anecdotal variances between concrete syntaxes and thus the opportunity to build lots of new parsers... Using the ASN.1 way, you only write one parser for each encoding format (BER,PER, XML, etc.) and that parser will serve either one or thousands of distinct uses... This is a good thing. bob wyman 
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