Java Reference
In-Depth Information
Chapter 2. XML Schema and the SOA Data Model
Introduction
XML is the linguafrancaof SOA. It is used for message payloads, application configuration,
deployment, discovery, runtime policies, and increasingly for representing executable lan-
guages such as BPEL that are central to the SOA landscape. Web service interfaces are rep-
resented with XML in the form of WSDL, and XML is used as the chief data transport mech-
anism in SOA. Because XML is so inextricably linked with web services development, and
because its inherent flexibility and expressiveness make it so powerful, it's a natural fit for
designing your data model for use within a SOA.
Designing data models as XML provides you with a valuable implementation-independent
foundation. It frees you to focus greater attention on ontology (the determination of what ex-
ists), and to be less subjected to vendor constraints. Because the libraries have at once become
more sophisticated and easier to use, XML is more attractive than ever as a place to start work-
ing with data models for your SOA.
Pundits and artists alike have long pointed out that our use of new communications
devices—whether cell phones, texting, IM, email, or PowerPoint—does not merely change
howwe communicate, but inevitably must augment or rearrange fundamentally whatwe
communicate. Marshall McLuhan summarized this in 1967 as “the medium is the message,”
meaning that the form of a message will subsume the ostensible content of the message itself.
As an architect, it's important to be aware of the subtle (or perhaps profound) shift in thinking
that can arise from using XML as a foundational layer for SOA. Of course, how big that shift
is typically depends entirely on your organization's environment.
One of the strengths of XML—indeed, its chief aim—is to be flexible. A lot of IT shops
around the world find themselves in the position of maintaining dozens upon dozens of ap-
plication silos, each one married to a rigid data model that must be accommodated with every
new update or rollout. Many such shops are now looking to SOA for answers. Using XML for
data exchange within your SOA encourages a more modal approach, offering contextual data
views that can flow, be transformed, and interact meaningfully across a variety of services and
tiers.
This chapter does not represent an introduction to XML, and is in no way intended to be
comprehensive in its coverage of XML, schema, or data binding. I am assuming that you are
relievedby this. You probably already have a basic understanding of XML and schema and
know what data binding is, or you wouldn't be reading this topic. If you don't, there are a lot
of topics and online tutorials to cover that for you.
