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objects on a remote system. Communication between objects on remote systems
uses an efficient, special-purpose wire protocol.
In the disconnected world, however, these services are a barrier to development. At
the most fundamental level, the wire protocols of Distributed COM and CORBA are
blocked by most Web firewall software. The largest barrier, though, 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 works 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 and Web Services
Independently of WDDX, the Web community has been working on how to solve the
general problem of open and flexible distributed computing using a model that is
closer to the traditional messaging and client-server systems.
The result is a set of specifications for Web Services, such as Simple Object Access
Protocol (SOAP), XML Protocol (XMLP), Web Service Description Language (WSDL)
and Universal Description, Discovery, and Integration (UDDI). The importance of
Web Services will increase as the technology matures.
WDDX does not compete with Web services. It is a complementary technology
focused on solving simple problems of application integration on the Web in a
pragmatic, productive manner at very low cost.
WDDX is a proven technology that has been shipping for several years. There are
numerous applications that leverage WDDX as a foundation for distributed
interoperability with other applications.
Currently, WDDX offers some unique advantages not present in Web Services:
Applications that take advantage of WDDX can continue to do so even when Web
Services become widely available. If need be, these applications could easily be
converted to use the upcoming Web Services standards. Only the service and data
interchange formats—not the application model—must change.
WDDX components
WDDX is based on XML, which is a World Wide Web Consortium (W3C)
Recommendation. The core of WDDX is an XML vocabulary, a set of components for
each of the target platforms to serialize and deserialize 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
It can be used by lightweight clients, such as browsers or the Macromedia Flash
player.
It can be used to store complex data structures in files and databases.
Chapter 18 Interacting with Remote Servers
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