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Knowledge: The Essence of Meta Data:
The Repository vs. The Registry

online columnist R. Todd Stephens, Ph.D.     Column published in DMReview.com
April 15, 2005
  By R. Todd Stephens, Ph.D.

A few months ago, I attended a meeting with a group of individuals discussing the idea of integrating a UDDI (universal description, discovery and integration) registry into the environment. Years ago, we built a Web Service Registry based the UDDI 2.0 specification utilizing, applications made available by HP, Microsoft and IBM. These UDDI registries are freely available to try out on the Web (links are provided at the end of this article). We eventually realized that the corporation just wasn't ready to utilize a UDDI standards registry, so we simple converted the registry to a repository.

Figure 1: The Repository and Registry

The title of the article is "The Repository versus The Registry," so does that indicate that there are differences between the two? Our organization has been using the terms interchangeably for years. But, this conversation made me rethink that philosophy, and a new theory has emerged. In today's environment, they are two different methodologies that serve many different functions. Figure 1 presents my new thinking and why these two applications need to be implemented into the corporation together to support service-oriented architectures (SOA).

A repository is basically a database application that contains information about an asset with the ability to attach unstructured documentation, and some implementations will actually contain the object itself (i.e., XML Artifacts). Traditionally, meta data focused on database and the ETL-type meta data. The evolution from physical data structures to logical models, component descriptions and system definitions extends the meta data environment to a whole new world of possibilities. New technologies such as XML and Web services are also requiring new forms of repositories than can manage the asset in a design and production environment. In many ways, the repository acts as an online product offering and should follow many of the same rules as electronic commerce applications. This allows us to define the product, service and an information framework in much of the same fashion that businesses build models for the online environment. The repository serves a different user than does the registry. Namely, the repository focuses on the early stages of the system development framework (SDLC) while the registry focuses on the latter stages. Does anyone actually believe that a designer or business analyst is going to be able to understand the components of the "tModel"? Maybe the descriptions are going to be so well written that each service is completely described in elegant detail. Especially since we did do such a superb job documenting code in the 1980s and meta-tagging our Web pages in the 1990s (Not). The repository serves the higher levels of the organization - architecture, design, analysis and even development. Employees at this level want to review the documentation, user guides, implementation and service level agreements. They want the repository to be easy to use and easy to access. They demand value-add services such as subscription services, semantic search, multiple classifications and community collaboration. None of which can be found in the current registry standard. The repository contains the asset, meta data elements and unstructured supporting documents.

The Web service registry is based on the UDDI model and basically serves to categorize information about businesses and the services that they offer, and it associates those services with technical specifications of the Web service. These technical specifications are usually defined using Web services description language (WSDL). WSDL describes what a Web service does, how it communicates and where it lives. A Web service consumer queries the UDDI registry to find the WSDL descriptions to determine how to use the Web service. A UDDI registry is itself a Web service. The UDDI specification defines an API based on simple object access protocol (SOAP) messages, with a WSDL description of the registry service. Most UDDI registries also provide a browser-based human interface (Shovohoda, 2005). A UDDI registry consists of the following data structure types:

businessEntity - The top-level XML element in a business UDDI entry, it captures the data partners require to find information about a business service, including its name, industry or product category, geographic location, and optional categorization and contact information. It includes support for "yellow pages" taxonomies to search for businesses by industry, product or geography.

businessService - The logical child of a businessEntity data structure as well as the logical parent of a bindingTemplate structure, it contains descriptive business service information about a group of related technical services including the group name, a brief description, technical service description information and category information. By organizing Web services into groups associated with categories or business processes, UDDI allows more efficient search and discovery of Web services.

bindingTemplate - The logical child of a businessService data structure, it contains data that is relevant for applications that need to invoke or bind to a specific Web service. This information includes the Web service URL and other information describing hosted services, routing and load balancing facilities and references to interface specifications.

tModel - Descriptions of specifications for Web services or taxonomies that form the basis for technical fingerprints; its role is to represent the technical specification of the Web service, making it easier for Web service consumers to find Web services that are compatible with a particular technical specification. That is, based on the descriptions of the specifications for Web services in the tModel structure, Web service consumers can easily identify other compatible Web services. For instance, to send a business partner's Web service a purchase order, the invoking service must know not only the location/URL of the service, but what format the purchase order should be sent in, what protocols are appropriate, what security is required and what form of a response will result after sending the purchase order. (Oracle, 2005)

Online UDDI Model: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/uddi/uddi/detailed_data_model.asp (Microsoft, 2005)

The conclusion is that both the repository and registry are going to be a requirement in the SOA environment. They simple serve two different customer groups. Eventually, vendors will move beyond the production environment and understand that semantic information and governance are critical to the long-term success of the service-oriented environment. Capturing asset meta data, integrating into the infrastructure and defining the architecture are wonderful goals, but governance is the key to the long-term success to a SOA. So many organizations simply focus on the shortest path possible when deploying service-based infrastructure and ignore the value-add from the repository. Vendors are already catching on; several registry products have or plan to have the ability to integrate documents into their registry. Of course, then it is no longer a registry but a repository, but why quibble over semantics. The repository and registry will play a critical role in the evolution of SOA and hopefully extend the impact of meta data to a new community of users.

Online UDDI Registries



For more information on related topics visit the following related portals...
Meta Data.

R. Todd Stephens, Ph.D. is the director of Meta Data Services Group for the BellSouth Corporation, located in Atlanta, Georgia. He has more than 20 years of experience in information technology and speaks around the world on meta data, data architecture and information technology. Stephens recently earned his Ph.D. in information systems and has more than 70 publications in the academic, professional and patent arena. You can reach him via e-mail at Todd@rtodd.com or to learn more visit http://www.rtodd.com/.

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