Metamodel and Metadata Relationships
Remember that our focus on metadata and its associated beneficiaries will now take a step up to a higher level of sorts, that of the metamodel. As discussed in the previous chapter, metamodels depict metadata relationships graphically, at the entity or object level. By grouping various metadata elements according to "what is being described," we create a series of entities. Each entity must have a primary key or identifier; relationships happen at the level of the primary key. For example, in relating customers to stores, we know that every customer visits one or more stores, and all stores are visited by one or more customers. Without getting into too much jargon, we can consider this a many-to-many relationship. The importance, however, rests with the fact that we identify stores, perhaps, by store numbers, and we identify customers, perhaps, by customer name and credit card number combined (a compound key). For simplicity, we assume no cash transactions.
Taking this analogy back to the world of metadata, remember that Data Element Business Name and Data Element Description were two pieces of metadata that were common throughout our examples. Where in the metamodel would they fit? It is often hard for newcomers to the world of metadata to realize that Data Element is a major topic or, in fact, what is being described by many of the other metadata elements, including Data Element Description. Hence, in a metamodel, Data Element would be an entity unto itself, and participate in many relationships, including relationships with specific types of data stores (files, databases, tables), entities within logical data models, reports, and applications, to name a few.
So as we evaluate any metamodel, we have to realize the level of our evaluation. Metamodels reflect a specific perspective on the way entities can connect. Each entity consists of a series of attributes, most typically our metadata elements; but sometimes, as previously discussed, other information needs to be tracked in order to maintain the stability of the metadata.
If we look again at the metamodel for our common metadata, illustrated in Figure 11-5, note that the two metadata elements that we are discussing (Data Element Business Name and Data Element Definition) are attributes of the Logical Data Element entity. This entity relates to Physical Data Element from the common perspective of all beneficiaries. The perspective is an important one to keep in our back pockets as we look at some of today's competing models.
Figure 11-5 Revisiting a metamodel