Cart
|
[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: XML Information Set Requirements, W3C Note 18-February-1999
 I agree with Sussna, by thinking out the concept of a document more fully a number of interesting ideas present themselves. In considering a document to be a stream or information set, it allows a distributive organization over a network. Instead of requiring the entire 'document' to be transferred en-masse as a file, it can be done piece-wise over a stream. Consider this just-in-time manufacturing of the 'document'. Naturally, you can think of cases where only part of the entire document is needed. Subsetting of the document tree is one of the features of XSL. Unifying these 2 ideas provides a new use for a DTD. It is not only a means to describe the valid structure of a document, but now can advertise the information available. A site can be described as capable of providing information sets in a set of structures defined by DTDs (or their replacement). A consuming application could request information by a pattern or query which would return the desired subset of information. What could be accomplished is a unified solution to problems addressed and/or recognized in SAX, XSL, queries, DOM, and fragments. It also provides a model for a data server as an XML 'document' constructor. In terms of architecture, it removes bottlenecks. Converting to a file model is expensive if the information is large and it can be used piecemeal on the other side. It is a worst-case solution. A demand-based stream model will create entire documents only if required by the ultimate consumer of the information and otherwise incrementally provide elements. Marc B McDonald, Principal Software Scientist Design Intelligence Inc, Seattle WA http://www.design-intelligence.com ---------- From: Jeffrey E. Sussna [SMTP:jes@k...] Sent: Friday, February 19, 1999 10:42 AM To: 'Clark Evans'; 'Marcus Carr' Cc: xml-dev@i... Subject: RE: XML Information Set Requirements, W3C Note 18-February-1999 I completely agree with Clark. As someone working with real-time XML streams, I think this is very important. In particular, the whole notion of "document" needs to be thought through very carefully in the context of 1999, rather than the context of 1990 when SGML was developed. If I may grow philosophical for a moment, I believe that XML is at a crossroads. That crossroads can be defined by examining the term "markup". I believe that XML is actually moving away from being "markup" oriented. First of all, one can easily imagine an XML document where all leaf-level elements are EMPTY, and contain all their semantics within attributes. In that case, there is nothing to be "marked up". Furthermore, when you apply XML to things like database record interchange, it really isn't a text-oriented environment anymore. I believe that XML points more towards type systems than markup. If you look at a programming language, it generally supports 2 things (I am being very poetic and not rigorous here): defining and instantiating data types, and defining and instantiating operations on data. XML supports the first. It provides a mechanism to create and exchange instances of data types between external systems that will provide the operations on those data. The realization that DTD's are inadequate, and that a more robust schema specification language is needed, points in the same direction. If you approach XML as a type system, the concept of document loses its first-class status (or at least should, in my opinion). It is interesting that the concept of document (even physical document as file) has crept into programming languages, and has caused problems there as well. The C language include directive is a physical rather than a logical mechanism. When you try to build a database-driven incremental build system, includes become problematic. I would like to encourage the XML community to 1) pay attention to the lessons of 30 years of development in the arena programming and type languages, and 2) not get bogged down by the historical baggage of the M in XML. Jeff Sussna -----Original Message----- From: owner-xml-dev@i... [mailto:owner-xml-dev@i...]On Behalf Of Clark Evans Sent: Thursday, February 18, 1999 9:09 PM To: Marcus Carr Cc: xml-dev@i... Subject: Re: XML Information Set Requirements, W3C Note 18-February-1999 Marcus Carr wrote: > I think you might be applying a meaning to that > phrase that it doesn't deserve - it doesn't call XML > a document standard, it uses the term "XML document", > with document defined in the XML recommendation as: > > "A data object is an XML document if it is well-formed, > as defined in this specification. A well-formed XML document > may in addition be valid if it meets certain further constraints." > > This allows you to use the phrases "XML data object" and > an "XML document" interchangeably. > > This isn't incongruous with stream markup - you just need to > consider the stream as an XML document. Seriously though, you > probably wouldn't have the same concerns about "XML data object" ... My concerns would be even greater. This conjures up in my mind a Java or C++ object where the complete stream has to be loaded in memory (or some other random-access medium) before it can be used. Yes, I know you can have a multi-threaded implementation so that you can start using the data object before it finishes reading, etc. However, given the object model it is *reasonable* for the niave programmer to ask for something at the _end_ of the stream. This will cause the call to block untill the stream ends. If "data stream" processing was treated with *equal* importance by the W3C committees, then they would see, in many cases, that this complementary approach is at least as good as, or in some cases far superior to an "data object" approach. Constantly viewing XML as a standard for the description of "data objects" and not "data streams" is a subtle, and important bias. It is taking object-orientation too far and discarding parallel stream processing, and it's related technologies like SAX and SAXON. :) Clark xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ and on CD-ROM/ISBN 981-02-3594-1 To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...) xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ and on CD-ROM/ISBN 981-02-3594-1 To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...) xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ and on CD-ROM/ISBN 981-02-3594-1 To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...) 
|
PURCHASE STYLUS STUDIO ONLINE TODAY!Purchasing Stylus Studio from our online shop is Easy, Secure and Value Priced! 
Download The World's Best XML IDE!Accelerate XML development with our award-winning XML IDE - Download a free trial today! Subscribe in XML format
|
|||||||||
