The Logical Meta Model

Regardless of whether the meta data repository is licensed or built, and regardless of the implementation method (centralized, decentralized, or distributed, as discussed in Step 10, Meta Data Repository Design), the meta data repository should support a logical meta model, which reflects the meta data requirements. As with business data, each component of meta data is unique by nature. It is important to define these unique meta data objects, their contents, their interrelationships, and their interdependencies, independent of how they will be stored or accessed. The technique for this activity is logical data modeling, only in this case it will produce a logical meta model.

A logical meta model is a data model that indicates objects, the relationships between the objects, and the cardinality and optionality of the relationships. The difference between a logical meta model for a meta data repository and a logical data model for a business application lies in the nature of the objects. Objects in a logical meta model represent meta data, such as entity, attribute, definition, domain, table, column, and index. Objects in a logical data model represent business data, such as customer, product, employee, account, and location.

The Entity-Relationship Meta Model

A logical meta model is created during the first meta data initiative and is expanded with each subsequent initiative. The logical representation of meta data objects should be captured as an E-R diagram because of its explicit definitions of the meta data objects, the relationships among them, and the contents of the objects. Figure 7.7 shows an example of an E-R meta model.

Figure 7.7. Entity-Relationship Meta Model. (Short vertical lines indicate "one," and the crow's feet indicate "many.")

An E-R meta model primarily helps people understand, communicate, and validate the meta data requirements. Therefore, an E-R meta model should be viewed as a requirements model to be used for evaluating meta data repository products and for setting a baseline when designing a customized meta data repository, even if its physical meta model (database design) ends up being object-oriented (OO).

Meta-Meta Data

Since meta data is the contextual information about business data, meta-meta data is the contextual information about meta data. Many components of meta-meta data are similar to those of meta data. For example, every meta data object should have components that cover name , definition, size and length, content, ownership, relationship, business rules, security, cleanliness, physical location, applicability, timeliness, volume, and notes. The meta-meta data for a meta data object might look like this:

• Name: Entity

• Relationship: related to one or many tables

• Security: read by all, updated by the data administrator

• Ownership: the data administrator

• Origin: ERWIN CASE tool

• Physical location: MDRSYSENT table

• Cleanliness: 2 percent missing data

• Timeliness: last updated on November 1, 2002

• Volume and growth: 2,391 rows, growth rate 1 percent annually