A revision becomes necessary when adjustments to the content or the catalog software must be made.

A change in the software landscape can also require revisions, such as when a new version of the Internet browser does not sufficiently handle the catalog as the previous version had.

Changes on the software side are usually manageable, especially when the catalog used to run reliably before. Changes on the software side are rather an exception than a rule.

In the majority of cases, the core of a revision consists only of changes to the contents.