Meta Data Repository Solutions

The solution to meta data silos is clearly an enterprise-wide meta data repository approach. This can be accomplished in one of three ways:

1. One centralized meta data repository database solution

2. A decentralized meta data solution that uses one integrated meta model but physically distributes the meta data across multiple databases

3. A distributed XML-enabled solution in which the meta data is XML-tagged and stored (kept) in the different types of proprietary tool dictionaries on different platforms

Regardless of which meta data repository solution is chosen , meta data repository projects and subprojects are large and costly. Therefore, any meta data repository solution should be built in iterations.

Centralized Meta Data Repository

A 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.

• Custom-built repository: Designing and building a customized centralized meta data repository is an alternative that should be considered . Since the meta data repository solution should be enterprise-wide, the meta models (both logical and physical) will be generalized and not application-specific. This means that there will not be a meta data repository for a marketing application and another one for a sales application; instead, there will be one centralized meta data repository for all applications. The advantages and disadvantages of building a customized centralized meta data repository are similar to those of building a customized business application (Table 10.1).

  Table 10.1. Advantages and Disadvantages of a Custom-Built Centralized Meta Data Repository

  Advantages	Disadvantages
  A customized database design incorporates all meta data requirements.	Full-time staff is needed to maintain the meta data repository database and the meta data reports .
  The front end for access and the interfaces to tools (ETL, OLAP, and so on) are custom designed to meet all requirements.	The front end for access and the interfaces to tools must be programmed and maintained , both of which are time-consuming processes.
  Reports as well as help functions are designed exactly as desired.	The meta data repository would have to be enhanced periodically (sometimes redesigned) because it cannot be built with all functionality from the start.
  Technicians have full control over the design and functionality of the meta data repository.	Content may become out of synch with the proprietary dictionaries of the tools and the DBMS.

• Licensed repository: Licensing (buying) a centralized meta data repository product is an attractive alternative to building one. Losing some of the benefits inherent in a customized solution is offset by gaining the advantages that come with licensing a vendor product (Table 10.2).

Table 10.2. Advantages and Disadvantages of a Licensed Centralized Meta Data Repository

Advantages	Disadvantages
Time is saved by not having to design and build a meta data repository database, interfaces, front end, and reports.	The "plain vanilla " version of the licensed product will probably not satisfy all meta data requirements. Therefore, a full-time administrator is needed to maintain and enhance the licensed product.
Most licensed meta data repository products come with interfaces, and most come with a full set of APIs.	There will be a learning curve to become familiar with the product's architecture, interfaces, and APIs.
If the meta data repository product is certified for the tools where the meta data resides, it will provide the tool interfaces.	The more sophisticated the meta data repository product is, the more expensive it is, and the more skills the technicians need to maintain it.

Decentralized Meta Data Repository

As 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

Advantages	Disadvantages
Various owners can maintain and manage their own sets of meta data separately.	Controlling redundancy across multiple meta data repositories and keeping the meta data consistent is difficult.
Meta data repository databases are smaller and easier to use because each database contains only those meta data components that are of interest to a specific group of business people.	It will take longer to maintain and manage multiple databases on multiple platforms. There could also be synchronization problems with new DBMS releases.
Each meta data repository can have its own meta model, that is, its own customized design.	Communication among the custodians of the various meta data repositories will have to increase. Plus, it will require maintaining a meta-meta model, which is an integrated (merged) overall architecture of multiple meta models.
Reports can be customized for each individual meta data repository.	Relating meta data across various databases may be difficult. For example, business meta data is not automatically linked to technical meta data if they reside on different databases.
A gateway makes the name and location of the meta data repository transparent to the person accessing it.	The architecture of this solution is more complicated and the learning curve to use multiple databases with potentially different designs may be high.

Distributed XML-Enabled Meta Data Solution

Although 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

Advantages	Disadvantages
XML tags enable access of meta data across any type of data storage through standardized categorization and tagging of meta data components.	The initial tagging of all meta data with XML tags is a manual and laborious process. Plus, XML tagging cannot be used for all meta data.
Meta data never has to be duplicated or moved from its original source (except for reporting purposes).	XML tags add to the storage requirements for the dictionary databases that store meta data (DBMS and tool dictionaries).
A gateway makes the location of the meta data transparent to the person accessing it.	A meta-meta model has to be created as a map of all the various types of meta data storage, each of which is designed according to its own unique meta model.
Standard Web search engines should be able to locate any meta data anywhere .	DBMS and tool vendors must follow industry standards [*] for meta data XML tags in order to enable seamless meta data access across all products. Multiple standards need to be supported.
Meta data and business data can be coupled and transmitted simultaneously .	Not all DBMSs and tools are XML-enabled. This is a bleeding-edge and unproven technology.

^[*] Meta data standards are being developed by two competing groups: the Meta Data Coalition (MDC, influenced by Microsoft) and the Object Management Group (OMG, influenced by Oracle). The jury is still out on which meta data standards will be adopted as the industry standards.