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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: SAX for Binary Encodings (preserving investment) (ASN.1and
 Bob Wyman wrote: >... > Fortunately, it appears that Objective Systems already provides a > SAX-like interface for ASN.1 defined binary encodings and OSS Nokalva > is working on a SAX interface for ASN.1 defined encodings. There is a > paper that talks about the Objective Systems implementation at: > http://www.obj-sys.com/docs/ASN1CEventHandlersWhitePaper.pdf This is a good thing to point to if you want to convince people that ASN.1 can't handle "real XML". Where are the attributes, processing instructions, etc.? However, assuming all of SAX *could* be implemented... > Reading the paper, it becomes clear why Objective Systems' > implementation is "SAX-like" rather than being simply "SAX." The > issues that caused them to diverge from plain-vanilla SAX are ones > that will need to be dealt with by any project which attempts to build > SAX support for binary encodings -- whether they are the ASN.1 defined > encodings or some new-fangled "binary XML" which might get invented > (but hopefully not patented...) > SAX assumes that the data it is reading is all of "character" > type. SAX has no access to a schema file and thus has no idea of the > real type of the characters it reads. However, a binary encoding will > typically pass data in a form more appropriate for its type. Thus, an > integer will be passed as something like a 32-bit value, not a string > of characters. So, to build a "pure SAX" interface to a binary > encoding, you would have to convert all the binary values to > characters before passing them to the SAX event handlers. Of course, > the first thing a lot of event handlers will do is convert the strings > back into binary types like integers. The result is, of course, often > wasteful silliness. It causes performance problems, memory > fragmentation due to all the string allocations, etc. > So, while SAX interfaces to binary encodings allow us to do > things like use XSLT processors on binary data, they also raise some > issues about the SAX interface itself. Knowing that people are already > implementing SAX interfaces to binary data, it probably makes sense to > carefully consider at this point how to handle this problem so that > standardized solutions can be implemented. That would be much better > than each developer or vendor coming up with their own interpretation > of what SAX for binary encodings looks like. > There are a number of possible solutions: > 1. Insist that all binary types be converted to strings. Well, yes. First implement SAX 2 with no exceptions. > 2. Define an "extended SAX" that passes data with descriptors > that show the type of data. Thus, a program would be told the type of > the data being passed and could call a ToString or ToInteger function > as needed. Yes, too. > 3. Provide a "mode switch" which could be called to modify the > behaviour of SAX. If "StringsOnly" was set to true, then only strings > would be generated, if "allowTypes" was set, then types would be > passed by descriptor. > 4. Other options? > What makes the most sense here? If the subject is interoperatility with XML applications, unquestionably the priority must be to implement SAX 2 as it is. The extension in 2 above could serve as a useful prototype for a "SAX 3" that can return non-string values. This API would be helpful both to ASN.1-encoding users who wish to obtain optimal performance and XML-encoding users who want to use schema-driven conversion to internal datatypes. Bob Foster > > bob wyman > > > > ----------------------------------------------------------------- > The xml-dev list is sponsored by XML.org <http://www.xml.org>, an > initiative of OASIS <http://www.oasis-open.org> > > The list archives are at http://lists.xml.org/archives/xml-dev/ > > To subscribe or unsubscribe from this list use the subscription > manager: <http://lists.xml.org/ob/adm.pl> > > 
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