Metadata is not only “about data”—it is also always data, itself. One person's data is another person's metadata. There is, in general, no difference between data and metadata; it's all a matter of perspective.
It is normal to think of metadata as being somehow “in orbit” around the data about which the metadata provides information. The existence of a metadata Web site that provides information about data Web sites affects global knowledge interchange in two ways.
When users are at the metadata Web site, their attention can be directed at one or more data Web sites, and users can know the reasons why.
When users are at the data Web site, they may derive more useful information if they also know about ...