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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: "Binary XML" proposals
 Al Snell wrote: > Christopher R. Maden wrote: > >If I get Al's Binary Structure Format, what the heck do I > > do with it? The drawbacks seem prohibitive and the benefits minimal. > > Dude, we covered this point... read the thread! What this thread has not covered, IMHO, is this: what you, or I, or any user of an XML document might *do* with it is determined primarily by what the needs and the abilities of that user are, and by the particular environment in which that document is used, far more than by any fixed understanding of what that document might 'mean'. One proposal earlier in the thread apparently visualized a 'binary XML' format as a way to hash and then ship around SAX events between applications, avoiding re-parsing with each use. This sort of thing is a well known and common practice of course, but it utterly misses a salient point of XML. It is inherent in the nature of XML that the text of a document be parsed anew for each use of that document, in the particular context of that use. XML applications begin by parsing because XML applications may be unique and idiosyncratic uses of XML documents, where the outcome of that parsing is determined by the environment in which it is done or by additional data available at that parse which is not accessible to other users of the same XML document. This is a uniqueness of XML, and one which affords an entirely new basis for distributed applications. Such artifacts of the present distributed processing orthodoxy as the two-phase commit protocol rely on a transparency which is offered by an homogenous enterprise network, but unavailable on an internetwork. On the homogenous network, nodes can recognize each other by their functions and have privileged, intimate knowledge of both the data structures and the sequence of process expected by other nodes with which they participate in distributed transactions. The node performing bank ATM processing knows the data structure which the node performing the account side of a withdrawal transaction expects, and both follow the same sequence of identical process steps, which they can reverse in identical order if it is necessary to rollback a transaction. In such an homogenous environment, the SAX events from parsing a given XML document at one node may well be identical to those from processing it at another, and could be shipped in fixed binary form between the two without any loss of information. In an internetwork topology, however, two nodes may share nothing but the ability to contact each other through the addressing scheme which has been overlaid onto constituent networks built on very different assumptions of process and of the expected form of data. Through internetworking those nodes may be able for the first time to exchange data, but the expected form or 'meaning'--let alone the proper uses--of that data may have nothing in common between the two. When that data is exchanged as XML text, with the fundamental expectation that it will be parsed afresh and then processed at each node in an environment and for purposes which are unique to that node, it is possible for the first time to execute distributed processing between utterly dissimilar parties. That new and unique benefit of the XML intellectual commons is the first thing lost to any canonical, let alone binary, representation of meaning. Respectfully, Walter Perry 
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