9.4 Transformation Techniques 197
The data are the same, but the point of view has changed. The point of view
depends strongly on the purpose for which the data were collected. Chang-
ing the purpose generally requires that one also change the point of view.
The point of view is especially important when information is being dis-
played. There are many examples of this. One can present a list of research
papers organized in many different ways: by topic, by author, by publication
date.
The point of view is also important when data are being processed. The
processing program expects to receive the data in a particular way. Even
when the source document has all of the necessary data, the data can easily
be in the wrong form. Indeed, unless the source document and program
were developed together (or they conform to the same standard), it is very
unlikely that they will be compatible.
The process of changing the point of view of an XML document is an exam-
ple of a transformation which is also called “repackaging” or “repurposing.”
Transformations in general are sometimes called “stylesheets” because they
were first used as a means of specifying the style (visual appearance) of a
document. Separating display characteristics from the content of a docu-
ment was one of the original motivations for the development of XML and
its predecessors.
Summary
- Transformation is the means by which information in one format and for
one purpose is adapted to another format for another purpose. - Information transformation is also called repackaging or repurposing.
9.4 Transformation Techniques
One of the most powerful features of XML is that it is especially well suited
to being transformed. There are many reasons for transforming data:
- The structure must be rearranged as in the microarray example in sec-
tion 9.3 above. - Some element and attribute names need to be changed.