Business semantic metadata. This is the kind of metadata that describes, in precise business terms, what each element of data actually means. Recall the discussion “What is a sale?” The business semantic metadata will define a sale as being, for instance:
The quantity and total order value of an order for a single product by a customer, before discount
The description should leave no room for ambiguity. It must be possible to define every entity, relationship, and attribute in the system.
Transformational metadata. This describes all the properties of the data element and includes:
Source system from which the element was extracted
1）Frequency of extraction
2）Changes that have been made
3）Level of retrospection that applies
4）Dependencies on other data elements
Again, this information should be held for every piece of information in the data warehouse.
Navigational metadata. This is the sort of metadata that comes with most products. It is metadata that enables the product to operate properly. For instance, the product might need to store information about the location of its own files and programs, etc.
All products claim to have metadata. This is because it is fashionable to have metadata, and vendors feel that it somehow enhances their products if the architectural diagrams can show a layer of metadata (checkout the EASI data architecture in Figure 7.1!!). One major RDBMS vendor used to have schema tables in which the tables, columns, users, etc., got stored. These schema tables are no longer schema tables; they are metadata and they've got diagrams to prove it. This is a good example of navigational metadata. When we in data warehousing refer to metadata, we generally mean the business semantic and transformational kind of metadata.
there are three basic kinds of metadata:
The quantity and total order value of an order for a single product by a customer, before discount
The description should leave no room for ambiguity. It must be possible to define every entity, relationship, and attribute in the system.
Source system from which the element was extracted
1）Frequency of extraction
2）Changes that have been made
3）Level of retrospection that applies
4）Dependencies on other data elements
Again, this information should be held for every piece of information in the data warehouse.
All products claim to have metadata. This is because it is fashionable to have metadata, and vendors feel that it somehow enhances their products if the architectural diagrams can show a layer of metadata (checkout the EASI data architecture in Figure 7.1!!). One major RDBMS vendor used to have schema tables in which the tables, columns, users, etc., got stored. These schema tables are no longer schema tables; they are metadata and they've got diagrams to prove it. This is a good example of navigational metadata. When we in data warehousing refer to metadata, we generally mean the business semantic and transformational kind of metadata.