10.7 Common Warehouse Metadata Interchange
10.7 Common Warehouse Metadata Interchange In most environments, IEBI is implemented with a variety of tools drawing data from a variety of sources. We have discussed how IEBI distributes data throughout the organization. Often, this information is delivered to many different decision support tools on various platforms. In today's environment, the traditional wisdom is that it is possible for a single metadata repository to implement a single metamodel to meet all the needs of an organization. The OMG chose instead to provide a single standard for the interchange of warehouse metadata. This single interchange is the CWMI, which is compliant with both MOF and UML notation. CWMI is a complete specification in that it provides a complete description of the semantics and syntax for IEBI tools and applications to exchange metadata. The specification defines a common warehouse metamodel, APIs, and interchange formats. Application and tools conforming to these specifications can exchange warehouse metadata. The specification actually consists of several elements that are based on the OMA. CWMI uses the MOF as the meta-metamodel, the UML as the graphical notation, and XML as the medium of information exchange between systems. As we can see in Figure 10.6, there is a relationship between each structure that we have discussed within the OMA. The entire structure is designed to represent metadata. Metadata is data, albeit a different type of data than what most people normally encounter. Being data, it requires its own metadata: meta-metadata. The model representing this meta-metadata is contained within the MOF, which is the meta-metamodel. This is the base of the entire structure. At the levels above the MOF, we see parallels between the data warehousing world and the other objects within the OMA. The UML is the common OA&D metamodel. In the same way, the Common Warehouse Metamodel is the common metamodel for the warehouse model. Figure 10.6. Relationships between CWMI, UML, and MOF. By basing CWMI on the UML and MOF, the OMG achieved several important objectives. First, these are proven technologies. Common Object Request Broker Architecture (CORBA), which is the specification for the programming interfaces to the OMA Object Request Broker, is just one example of a successful application of OMA. By using a proven technology, CWMI can create a stable, enterprise-level environment that is generic and independent of any specific data warehouse implementation. This implementation-independence allows CWMI to be portable and usable on any computer system. The intent of the OMG was to define an interface rather than attempt a specification for a common metadata repository. While this may be the case with the actual specification, it does not preclude the data warehouse architect from establishing this central metadata repository on his or her own. As a common metadata interface, CWMI enables the establishment of such a central repository. Figure 10.7 demonstrates the relationship between CWMI and the central repository. In the diagram, we see that there is one central repository. ETL and decision support tools can contribute and extract metadata via CWMI. Figure 10.7. CWMI and a central metadata repository. The importance of a central metadata repository cannot be overemphasized. The repository is the source of the truth. In an environment where there is no such repository, there is no definitive source of the metadata. In an environment with such a repository, the metadata contained within the central repository is the metadata. Any metadata conflicting with this central system is by definition ignored. In such a role, the repository becomes the center of the IEBI system; all other systems within this information infrastructure will need to read and write from this repository. To fulfill the requirements driven by such an environment, we can use standard database technology to maintain this repository. This is of course what the repository isa database. It just happens to be a database of metadata.  |
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EAN: 2147483647
Pages: 113