Chapter 13 - Chapter 13. Warehouse Metadata Metadata have...

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Chapter 13. Warehouse Metadata Metadata have traditionally been defined as data about data. While such a catchy statement may not seem very helpful, it is actually quite appropriate as a definition—metadata are a form of abstraction that describes the structure and contents of the data warehouse. Metadata Are a Form of Abstraction It is fairly easy to apply abstraction on concrete, tangible items. Information technology professionals do this all the time when they design operational systems. A concrete product is abstracted and described by its properties (i.e., data attributes)—for example, name, color, weight, size, price. A person can also be abstracted and described through his name, age, gender, occupation, etc. Abstraction complexity increases when the item that is abstracted is not as concrete; however, such abstraction is still routinely performed in operational systems. For example, a banking transaction can be described by the transaction amount, transaction currency, transaction type (e.g., withdrawal), and the date and time when the transaction took place. Figure 13–1 and Figure 13–2 present two metadata examples for data warehouses; the first example provides sample metadata for warehouse fields. The second provides sample metadata for warehouse dimensions. These metadata are supported by the Warehouse Designer software product that accompanies this book. Figure 13-1 Metadata Example for Warehouse Fields Figure 13-2 Metadata Example for Warehouse Dimensions
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In data warehousing, abstraction is applied to the data sources, extraction and transformation rules and programs, data structure, and contents of the data warehouse itself. Since the data warehouse is a repository of data, the results of such an abstraction—the metadata—can be described as "data about data." Why Are Metadata Important? Metadata are important to a data warehouse for several reasons. To explain why, we examine the different uses of metadata. Metadata Establish the Context of the Warehouse Data Metadata help warehouse administrators and users locate and understand data items, both in the source systems and in the warehouse data structures. For example, the date value 02/05/1998 may mean different dates depending on the date convention used. The same set of numbers can be interpreted as February 5, 1998 or as May 2, 1998. If metadata describing the format of this date field were available, the definite and unambiguous meaning of the data item could be easily determined. In operational systems, software developers and database administrators deal with metadata every day. All technical documentation of source systems are metadata in one form or another. Metadata, however, remain for the most part transparent to the end users of operational systems.
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Chapter 13 - Chapter 13. Warehouse Metadata Metadata have...

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