In addition to document classes, there are also different document types. There are letters, e-mails, presentations, memos, spreadsheets, project plans, product descriptions etc.
They are purely descriptive characteristics of a document. cattaDoc includes by default the most commonly used document types, and more types can be added on the fly by system administrators, reflecting the current use of cattaDoc. There is a screen for adding document types in the System administration part of cattaDoc.
Document types are related to document classes, ie. they are specific for a given document class.
Library files share document types with documents, but also have a few types specific for library files, e.g. binary and code.
All file/documents in cattaDoc can be related to other documents as an appendix. So you can always register the whole "envelope", if you like.
All file/documents can also be related to each other as responses. You can therefore in cattaDoc easily document a chain of documents consisting of replies and responses.
From version 4.1 of cattaDoc, both appendices and responses can be related to an unlimited number of other documents, both as main documents and as appendix and response. Ie. there is a many-to-many relationship for both appendices and responses.