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The OASIS UDDI Specifications Technical Committee has recently published a new Technical Note that describes a much richer approach to using UDDI to model a WSDL description of a Web service. This is a significant improvement over previous methods that needs some exploration and explanation.
This article is the first in a series that examines this new approach to modeling WSDL in UDDI and shows how to write applications that support it. In this article, the background to the new Technical Note is described, followed by an explanation of the approach taken. The reader is assumed to be familiar with WSDL 1.1 and UDDI V2.
The second article will examine the types of query that can be executed against this UDDI model.
The third article will present a more complex example than the one in the Technical Note, including screen shots showing how to publish the UDDI entities and how to construct the types of query described in the Technical Note.
The final articles will describe how to write JavaTM applications that can publish these models to UDDI and issue the queries, using UDDI4J.
A Technical Note is a document published by the OASIS UDDI Specifications Technical Committee that provides guidance on how to use UDDI registries. Once an approach described in a Technical Note has been implemented and become established, it becomes a candidate for a Best Practice.
Why is a new Technical Note needed?
The existing Best Practice on using WSDL and UDDI is limited in scope and focussed on the WSDL binding, whereas the programming models that are emerging for Web services such as JAX-RPC are focussed on the WSDL portType.
The existing Best Practice provides no support for queries other than the very simple query of finding tModels that relate to WSDL descriptions. No other information is captured so there is no other information to issue queries against.
The existing Best Practice did not encompass the WSDL service and port elements which meant that there was no standard way to find implementations of a given portType or binding.
The goals of the new Technical Note
The goals of the new Technical Note are as follows:
- Support the modeling of WSDL portTypes in UDDI.
- Support the modeling of WSDL bindings in UDDI, in a way that is compatible with the Version 1 Best Practice.
- Support the modeling of WSDL services and ports to allow queries to find implementations of particular portTypes and/or bindings.
- Provide a model that is consistent when manipulated through either the UDDI V2 API or the UDDI V3 API.
- Support any logical or physical structure of WSDL description, any number of portTypes etc. and any number of separate files/resources.
- Capture sufficient information from the WSDL description without excessive duplication of information.
- Support precise and flexible UDDI queries against the model.
The Technical Note introduces nine new tModels that must be provided by a UDDI registry in order to support the approach described in the Technical Note. Six of these tModels represent new Category Systems and the remaining ones are other types of tModel. These new tModels are described in the following sections.
The Technical Note makes extensive use of categorization and introduces six new Category Systems:
- WSDL Entity Type Category System
- XML Namespace Category System
- XML Local Name Category System
- WSDL portType Reference Category System
- Protocol Category System
- Transport Category System
These new Category Systems are described in the following sections.
WSDL Entity Type Category System
This Category System is used to identify UDDI entities that correspond to
WSDL entities. It is currently used with the following UDDI entities:
- tModels
- businessServices
As WSDL allows a portType and a binding to have the same name a keyedReference using this Category System may be the only way to differentiate two tModels, one of which relates to a portType and the other to a binding.
XML Namespace Category System
As its name suggests, this Category System is used to represent any XML
namespace, not just WSDL-related namespaces. It is defined in the WSDL
Technical Note because that is the first context in which it is required but it
can be used with any XML-based modeling approach. Capturing the XML namespace
of an entity enables precise queries to be made using full XML entity names,
consisting of both a namespace name and a local name.
XML Local Name Category System
This is another general XML Category System which is used to hold a local
name when the name of the corresponding UDDI entity cannot be the same as the
XML element's local name.
WSDL portType Reference Category System
This Category System is used to represent the link between a binding and a
portType by allowing one UDDI entity to refer to another UDDI entity by storing
its key as the keyValue attribute value of a keyedReference relating to this
Category System.
Protocol Category System
This Category System allows user-defined protocol tModels to be incorporated
into the approach described in the Technical Note.
Transport Category System
This Category System allows user-defined transport tModels to be
incorporated into the approach described in the Technical Note.
The Technical Note also introduces several other canonical tModels and these are described in the following sections.
SOAP Protocol tModel
This tModel is used to represent the use of the WSDL SOAP binding.
HTTP Protocol tModel
This tModel is used to represent the use of the WSDL HTTP binding. Note that
this is a different tModel to the HTTP transport tModel which is used with the
SOAP protocol tModel to represent the use of a SOAP/HTTP binding.
WSDL Address tModel
This tModel is used when a WSDL Implementation Document is used.
How to Model WSDL Descriptions in UDDI
This section describes the approach defined in the Technical Note. The model for each of the WSDL entities is described. The description is in terms of the UDDI V2 API and Data Structures specifications. There is very little difference in the UDDI V3 model. For details see the Technical Note.
A WSDL portType is represented by a UDDI tModel. This tModel is categorized, using the WSDL Entity Type Category System described above, as a WSDL portType tModel to distinguish it from any other type of tModel.
The name of the portType tModel is the name of the portType. This goes against the advice in the UDDI Data Structure Specification that a tModel name should be formatted as a URI. The options considered for the tModel name were:
- Use the portType name. This was the option chosen.
- Use a combination of the portType name and the namespace name.
- Use some other URI and put both the local name and the namespace name in the tModel
categoryBag.
Option 2 would make it more difficult to search on either the namespace name
or the portType name. Option 3 would make it more difficult to search on the portType name and there would be no
information represented in the tModel name. Options 2 and 3 could be combined but that would introduce redundant
data as both the namespace name and the portType name would be stored twice,
once in the categoryBag and once as part of the tModel name.
The namespace of the portType is represented by a keyedReference in the
categoryBag of the portType tModel. This keyedReference relates to the XML
Namespace Category System.
As the detailed information in the portType relating to messages, operations etc., is not duplicated in UDDI the portType tModel must refer to the WSDL document in which the portType is defined so that tools that need this information such as application development tools that wish to generate a programming language interface from the portType, or sophisticated systems that wish to validate requests against the definition of the portType can retrieve the WSDL document. The tModel overviewURL is used to hold the URL for the WSDL document.
A WSDL binding is represented by a UDDI tModel. This tModel is categorized as a WSDL binding tModel to distinguish it from any other type of tModel. This categorization uses the same Category System as the portType tModel, but with a different keyValue value to differentiate a binding tModel from a portType tModel.
The name of the binding tModel is the name of the binding. The options above relating to the name of a portType tModel were also considered for binding tModels, and the same approach was chosen.
The namespace of the binding is represented by a keyedReference in the
categoryBag of the binding tModel. This keyedReference relates to another new
Category System defined in the Technical Note for the purpose of holding an XML
namespace name.
As the detailed information in the binding relating to document/literal etc. is not duplicated in UDDI the binding tModel must refer to the WSDL document in which the binding is defined so that tools that need this information can retrieve the WSDL document. The tModel overviewURL is used to hold the URL for the WSDL document.
The link between the binding and the portType it relates to is represented
by another keyedReference in the categoryBag of the binding tModel. The
tModelKey value of this keyedReference is the key of a new canonical tModel
representing a Category System that has valid values of the keys of other
tModels, specifically portType tModels. The keyValue value of the
keyedReference is the key of the portType tModel that represents the portType
that the binding relates to.
The protocol that the binding represents is represented by another
keyedReference in the categoryBag of the binding tModel. The tModelKey value of
this keyedReference is the key of a new canonical tModel representing a
Category System that has valid values of the keys of other tModels,
specifically protocol tModels. The keyValue value of the keyedReference is the
key of the appropriate protocol tModel. In the common case of SOAP/HTTP, a new
SOAP protocol tModel has been defined by the Technical Note and the key of this
tModel would be used. Other protocol tModels can be published and they would
automatically be valid for this new Category System.
If the binding represents a transport in addition to the protocol, then a
similar approach is used to represent the transport information. There is
another new canonical tModel defined in the Technical Note that has valid
values of the keys of transport tModels, and a keyedReference relating to this
Category System is added to the binding tModel. In the common case of
SOAP/HTTP, the standard HTTP transport tModel is used. Other transport tModels
can be defined to UDDI and they automatically become valid for this Category
System.
For compatibility with the Version 1 Best Practice a binding tModel should be categorized using wsdlSpec.
A WSDL service is represented by a UDDI businessService. If the WSDL service represents a Web service interface for an existing service then there may be an existing UDDI businessService that is relevant, in which case the WSDL information can be added to that existing service. If there is no suitable existing service then a new UDDI businessService can be created.
There are two approaches to representing a WSDL service and its ports:
- If there are no extensibility elements used in the WSDL service, and the address in the extensibility element on each port is of a form that can be represented as a UDDI accessPoint then the normal approach is to represent all of the information from the service and its ports in UDDI and not to refer to the WSDL file containing the service.
- If this is not possible then an alternative approach is defined in which a reference to the WSDL containing the service is kept and the WSDL document must be retrieve to obtain the information.
A WSDL port is represented by a UDDI bindingTemplate. The containment relationship between a WSDL service and its ports is exactly mirrored by the containment relationship between a UDDI businessService and its bindingTemplates.
The approach to mapping WSDL to UDDI described in the Technical Note is summarised in Figure 1.
Figure 1. Summary of UDDI-WSDL Mapping
This article has given an introduction to the background to the new Technical Note on using UDDI and WSDL, and described the main points of the approach described in the Technical Note.
Subsequent articles in this series will describe the types of queries that this new approach enables, present a more complex example, and show how to write Java applications to publish to UDDI in accordance with the Technical Note and how to issue typical queries against the new UDDI model of WSDL.
- Read the other parts of this series:
- "A new approach to UDDI and WSDL, Part 2" (developerWorks, September 2003) describes the queries that are supported by the approach defined in the new Technical Note.
- "A new approach to UDDI and WSDL, Part 3" (developerWorks, October 2003) describes how to publish and query the UDDI model for the WS-I Sample Application, following the approach defined in the new Technical Note.
- "A new approach to UDDI and WSDL, Part 4" (developerWorks, October 2003) describes how to publish and query the UDDI model for the WS-I Sample Application, following the approach defined in the new Technical Note.
- "A new approach to UDDI and WSDL, Part 5" (developerWorks, October 2004) describes how to apply the approach defined in the new OASIS UDDI Technical Note to query from a Java application.
- "Understanding WSDL in a UDDI registry, Part 1" (developerWorks, September 2001) describes the previous Best Practice for using WSDL and UDDI together.
- "Understanding WSDL in a UDDI registry, Part 2" (developerWorks, September 2001) describes various scenarios relating to the previous Best Practice for using WSDL and UDDI together.
- "Understanding WSDL in a UDDI registry, Part 3" (developerWorks, November 2001) describes Java applications that implement the previous Best Practice for using WSDL and UDDI together.
- The OASIS UDDI Specifications Technical Committee is now responsible for UDDI standards.
- This article is based on the recent Technical Note "Using WSDL in a UDDI Registry, Version 2.0" which has recently been published as an official Technical Note by the OASIS UDDI Specifications Technical Committee.
- The previous Best Practice "Using WSDL in a UDDI Registry, Version 1.08" has been updated by the OASIS UDDI Specifications Technical Committee since the previous developerWorks articles were written.
- Access Web services knowledge, tools, and skills with Speed-start Web services, which offers the latest Java-based software development tools and middleware from IBM (trial editions), plus online tutorials and articles, and an online technical forum.
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- Want more? The developerWorks SOA and Web services zone hosts hundreds of informative articles and introductory, intermediate, and advanced tutorials on how to develop Web services applications.
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