An Overview Of Distributed Data For The Web; Wddx Components - MACROMEDIA COLDFUSION STUDIO 4.5-USING COLDFUSION STUDIO Use Manual

70

An Overview of Distributed Data for the Web

Web Distributed Data Exchange (WDDX) is an Extensible Markup Language (XML)
vocabulary for describing complex data structures such as arrays, associative arrays,
and recordsets in a generic fashion so they can be moved between different
application server platforms and between application servers and browsers using only
HTTP.
Unlike other approaches to creating XML-based generic distributed object systems for
the Web, WDDX is not designed as an analog of traditional object programming
languages. These approaches use XML as a generic descriptor for initiating remote
procedure calls between different object frameworks. This is a valuable approach to
the problem of using traditional object-based applications to the Internet, but it is
more useful as a bridge between different programming paradigms than it is as a
Web-native methodology for distributing structured data between application
frameworks.
There are several problems with merging the distributed object model of computing
with the Internet. Primarily, this model was designed with a completely different vision
of what general internetworking would look like. Instead of the "dumb and
disconnected" model of HTTP, distributed computing was built on the assumption of
rich network services that would allow resources on remote machines to act like local
components. These services allow an application on one system to find, invoke, and
maintain state with objects on a remote system. Communication between objects on
remote systems uses an efficient, special-purpose wire protocol.
But these services are a barrier to development in the disconnected world. At the most
fundamental level, the wire protocols of DCOM and CORBA are blocked by most Web
firewall software. But the largest barrier is that client-server oriented distributed
computing frameworks impose a development methodology that is radically different
from that of the Web. This methodology excludes the vast majority of developers
building Web applications whose main tools are tag-based markup languages and
scripting. While WDDX will work with systems that support component object
development paradigms, there is a large set of applications that can benefit from the
general characteristics of a distributed data system without the client-server overhead.

WDDX Components

The core of WDDX is the XML vocabulary and a set of components for each of the
target platforms to serialize and de-serialize data into the appropriate data structure
and a document type definition (DTD) that describes the structure of standard data
types. Functionally, this creates a way to move data, its associated data types, and
descriptors that allow the data to be manipulated on a target system between arbitrary
application servers.
WDDX is based on XML 1.0, which is a W3C Recommendation. Other W3C efforts,
such as the XML-Data proposal and metadata formats such as the Resource
Description Framework (RDF), have application to WDDX. The WDDX DTD supports