Technical Architecture
Figure
6-2 depicts the makeup of the UDDI project. The UDDI Business Registry
(UBR), also known as the Public Cloud, is a conceptually single system built
from multiple nodes that has their data synchronized through replication. A
series of operator nodes each hosts a copy of the content. The global grouping
of operator nodes is jointly known as the UBR. Operator nodes replicate
content among one another. Accessing any individual operator node provides the
same information and quality of service as any other operator node. Content
inserted into the UBR is done at a single node, and that operator node becomes
the master owner of that content. Any subsequent updates or deletes of the
data must occur at the operator node where the data was inserted.
Figure 6-2. The UDDI initiative
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Note that the scope of the UDDI project is much more than the UBR; a
company can provide a private operator node that is not part of the UBR.
Private nodes do not have data synchronized with the UBR, so the information
contained within is distinct. A grouping of companies can also create a
"private cloud" of nodes that have information replicated between their
private nodes, but that replication sequence will not have any interaction
with the UBR nodes.
The UBR has widely accessible inquiry services, but services may be
published only by authenticated entities. Any business can create an operator
node and make it available over the Internet and part of the UBR. Private
operator nodes can define the access rules for their nodes on a case-by-case
basis. They can follow the same model as the UBR or make the restrictions
looser or tighter.
Companies will likely set up private UDDI nodes. Even though use of these
nodes will probably be limited in the near future, quite a few companies are
showing interest in setting up private registries for internal or B2B
operations. Industry groups are also discussing options for meeting the
demands of their individual sector.
Many products have either been created or are being expanded to allow
companies to create their own public and private UDDI registries. For example,
BEA WebLogic Server and IBM WebSphere both intend to ship a fully compliant
UDDI Server embedded within the application server sometime in 2002. Other
companies, such as Systinet, HP, Oracle, SAP, Cape Clear, The Mind Electric,
and Silverstream, have created J2EE-compliant UDDI implementations that work
with existing application servers, including Tomcat, BEA, and IBM. Microsoft
has an implementation based upon .NET. Additionally, two open source J2EE UDDI
projects are in development: Bowstreet's jUDDI (http://www.juddi.org/) and JP Moresmau's
pudding (http://www.opensorcerer.org/).
UDDI Specifications and Java-Based APIs
This section discusses the different specifications that make up the UDDI
initiative and the options available to developers writing Java programs that
interact with a UDDI registry.
UDDI Specifications
The UDDI project also defines a set of XML Schema definitions that describe
the data formats used by the various specification APIs. These documents are
all available for download at http://www.uddi.org/. The UDDI project
releases their specifications in unison. The current version of all
specification groups is Version 2.0. The specifications include:
- UDDI replication
- This document describes the data replication processes and interfaces to
which a registry operator must conform to achieve data replication between
sites. This specification is not a programmer's API; it defines the
replication mechanism used among UBR nodes.
- UDDI operators
- This document outlines the behavior and operational parameters required
by UDDI node operators. This specification defines data management
requirements to which operators must adhere. For example, node operators are
responsible for durable recording and backup of all data, ensuring that each
business registration has a valid email address associated with it, and the
integrity of the data during deletions (e.g., deleting a business means that
all of its service entries must also be deleted). This document is not a
programmer's API and private registries are not required to support it.
- UDDI Programmer's API
- This specification defines a set of functions that all UDDI registries
support for inquiring about services hosted in a registry and for publishing
information about a business or a service to a registry. This specification
defines a series of SOAP messages containing XML documents that a UDDI
registry accepts, parses, and responds to. This specification, along with
the UDDI XML API schema and the UDDI Data Structure specification, makes up
a complete programming interface to a UDDI registry.
- UDDI data structures
- This specification covers the specifics of the XML structures contained
within the SOAP messages defined by the UDDI Programmer's API. This
specification defines five core data structures and their relationships to
one another.
The UDDI XML API schema is not contained in a specification; rather, it is
stored as an XML Schema document that defines the structure and datatypes of
the UDDI data structures.
Java-Based APIs
The UDDI specifications do not directly define a Java-based API for
accessing a UDDI registry. The Programmer's API specification only defines a
series of SOAP messages that a UDDI registry can accept. Thus, a Java
developer who wishes to access a UDDI registry can do so in a number of ways:
- Using a Java-based SOAP API
- A Java programmer can use an API that creates SOAP messages containing a
UDDI XML document. The Java programmer would be have to create each XML
document by hand and insert this document into the body of each SOAP
message. This approach would require that a developer understand the
ordering of the SOAP messages that a UDDI registry accepts and format each
SOAP message properly.
- Using a custom Java-based UDDI client API
- Some companies, such as Systinet, have created client APIs for accessing
a UDDI registry. These APIs have classes and constructs that represent the
data structures and messages supported by UDDI. These APIs also allow you to
interact with a UDDI registry without knowing the specifics of SOAP or the
XML messages and data structures that UDDI interacts with. These custom
libraries work with any UDDI registry, so you can use Systinet's library to
access Microsoft's UBR node.
- Using JAXR
- The JAXR specification defines a standardized way for Java programs to
access a registry. JAXR allows developers to write code that can access
several different registries, including UDDI and the ebXML
Registry/Repository. JAXR's programming constructs don't mimic those used by
UDDI, but this API gives you a common way to access a variety of different
registry types, whereas a custom Java-based UDDI client API can access only
a UDDI registry. The trade-off for portability is dealing with the
additional layer of abstraction required by JAXR. JAXR is currently in an
early preview release
To get you up to speed with UDDI, this chapter presents a simple UDDI
example implemented three times--one time for each technique. Apache SOAP is
used to develop a client that uses a Java-based SOAP API, Systinet WASP UDDI
Client Package demonstrates a custom Java-based UDDI client API, and a JAXR
client shows how JAXR's abstract approach looks to the developer. However, as
more details of UDDI are explained, the examples use the Apache SOAP
implementation because it allows us to focus on the details of XML and UDDI.
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