Transforms can automate data exchange.
We've told you that XML, in addition to structuring and validating data, also provides powerful ways to repurpose or reorganize that data. The mechanism for doing that is called an Extensible Style Sheet Language Transformation (XSLT), or more simply, a transform. (This is why .xsl is the file name extension for a transform file.)
A transform provides a set of rules (yes, more rules) for converting data described by one set of tags into data described by another set of tags.
For example, say your sales department stores its data in Excel workbooks, and your accounting department needs that information imported into a database. A transform can write data from preselected cells in the worksheet into the correct fields in the database.