The solution to meta data silos is clearly an enterprise-wide meta data repository approach. This can be accomplished in one of three ways:
Centralized Meta Data RepositoryA centralized meta data repository is the most popular solution and the easiest to implement because there is only one database, either relational or object-oriented, and only one application to maintain (Figure 10.2). Figure 10.2. Centralized Meta Data Repository
Updating the meta data repository does not have to be coordinated across databases, and retrieving the meta data from the repository can easily be accomplished with a simple GUI front end or Web application. A centralized meta data repository solution can either be custom built or licensed from a vendor.
Table 10.2. Advantages and Disadvantages of a Licensed Centralized Meta Data Repository
Decentralized Meta Data RepositoryAs the term implies, a decentralized meta data repository solution stores the meta data in multiple databases in multiple locations (Figure 10.3). Figure 10.3. Decentralized Meta Data Repository
Commonly accessed meta data components could be replicated across multiple databases, but great care must be taken to keep those components consistent. A gateway directs the meta data access calls to the appropriate database to retrieve the desired meta data. There are some distinct advantages and disadvantages to this solution, whether it is built in-house or licensed from a vendor (Table 10.3). Table 10.3. Advantages and Disadvantages of a Decentralized Meta Data Repository
Distributed XML-Enabled Meta Data SolutionAlthough the most promising meta data repository answer is a distributed XML-enabled meta data solution, it is also the most difficult to implement because it takes the concept of a decentralized meta data repository to the next level. Rather than storing meta data across multiple databases, in an XML-enabled solution the meta data remains at its originating location, that is, in the various tool dictionaries (Figure 10.4). Figure 10.4. Distributed XML-Enabled Meta Data Solution
A gateway acts as a directory to the various locations where the meta data components are stored (e.g., the DBMS system catalog tables or the ETL tool dictionary). Vendors are vigorously exploring this "bleeding-edge" solution because it reduces the necessity for double maintenance of the meta data. Double maintenance refers to maintaining the meta data in the originating sources (DBMS and tool dictionaries) as well as maintaining it in the separate meta data repository database. Table 10.4 lists the advantages and disadvantages of this solution. Table 10.4. Advantages and Disadvantages of a Distributed XML-Enabled Meta Data Solution
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