TABLE OF CONTENTS Metadata has gone from being a documentation aid to being a central part of a development environment, and in some cases it has become the application itself. As "data about data" it is almost pure semantics; that is, it stores the meaning of the data it describes.
| Metadata | Metadata is data about data. |
Unfortunately, metadata is at its most powerful in situations when it is crossing many levels of abstraction, and therefore it is sometimes hard to comprehend. In this chapter we discuss a real life example in a fair bit of detail to see how to apply metadata concepts to everyday applications. This will provide grounding for a subsequent discussion on semantically inspired systems.
The list of tasks in Figure 6.1 shows the relationship between data and metadata. In the absence of metadata, there is often little we can do with data. Before we delve into what we can do with metadata, it is important to explore the history of metadata so we can understand where it is now.
The business systems industry has changed metadata from being a data dictionary (documentation about the fields used within an application) to being a style of development that recognizes that the definitions of the data are subject to change in the same way as the rest of the data in an application. We have moved from metadata being an afterthought to being an architectural principle. Let's review how this...
