XML and Transactions on the Web

Of course Enterprise Java Beans (EJB) and the Common Object Request Broker Architecture (CORBA) don't have the whole field to themselves. Other protocols are being considered for various bits of the grand Web based e-commerce system.

New, Competing Protocols

There are a number of competing protocols on the horizon which may overtake CORBA and the Internet Inter-ORB Protocol (IIOP) for specific duties. Briefly these are they:

Extensible Markup Language (XML)

XML is a derivation of the Standard General Purpose Markup Language (SGML) just like the Hyper Text Markup Language (HTML) which describes the structure of these pages. XML is somewhat more flexible than HTML and it is perfectly possible to specify quite complicated structures in XML so that the XML takes on some of the features of an RPC. This has now been formalized in at least two specifications (Web Distributed Data Exchange (WDDX) and the almost eponymous XML-RPC), we are sure there are several more. These will no doubt acquire Transactional semantics soon, if not by the time you've read this article.

HTTP Next Generation (HTTP-NG)

HTTP-NG, now, recently seems to have come to a close. It was conceived as the Next Generation of Hyper Text Transfer Protocol, the protocol which brought you this page. It was recognized that HTTP had some deficiencies which could be addressed by a later iteration of HTTP and this was a working suggestion. The new protocol's specification started to acquire more of the properties of a general purpose RPC and again no doubt Transaction Semantics if things had continued. At the present moment HTTP-NG is in abeyance and the promoters, The World Wide Web Consortium (W3C) does not plan any follow-up activities.

Transaction Internet Protocol (TIP)

This protocol has been promoted by Microsoft and Tandem (now part of Compaq) in the past as a method of putting Transactional RPCs on the net. The RPCs are based on DCE's without the rest of DCE (so they were effectively Microsoft's). The whole thing could be considered an extension of Microsoft's DCOM architecture. This went through the IETF and has emerged as a proper Internet RFC (2371). Apart from some demonstration software not much more has been done on this, and interest generally seems to be subsiding in it.

It seems to us that XML will play an increasingly important rôle in Web based Transactional systems. It seem likely that the traditional form based system may in time be replaced by an XML RPC based one, particularly in inter-business transactions. Then again it may be imprudent to completely dismiss form based systems for with many systems there may be no advantage gained with using the additional complexity of an XML RPC. Further the XML RPC arena has yet to demonstrate a clear leader with two prominent specifications and methodologies. For what it's worth, at the time of writing (November, 1999) the backend scripting folks, PHP Hypertext Preprocessor (PHP), appear to have plumped for WDDX (in their next generation version 4). The interpretation of the XML RPC and indeed XML generally is still problematic. Only the latest versions of Microsoft's Internet Explorer claim to support XML so other browsers have to rely on Java programs to do the coding and decoding. In this they will be slower and the protocol will necessarily have a higher overhead than a pure RPC based protocol such as DCE's or IIOP. It is, however, an interesting half way house which is gaining some momentum.

Microsoft have been putting an increasing focus on XML based work. XML, it seems, was originally thought of as a super HTML, to allow the communication of things such as musical scores, mathmatics, chemistry and other documents encoded with richer structures than HTML would allow. There are examples of such documents in the field of business too. Ones that require such a rich structure are to be found in Orders for Goods between companies, Invoices and other such paraphanalia that keep commerce in good order. For a long time Electronic Data Interchange (EDI) has been used to provide the necessary structure. Several vendors are now working on standards to provide EDI and EDI like services layered on XML (such as XML/EDI). Microsoft are leading in this area, promoting an EDI over XML solution they term BizTalk.

$Date: 2009/10/18 10:30:30 $