All files have a common behavior controlled by the ISPFFile and ISPFBusinessFile interfaces. All file classes realize these interfaces; this provides the relationship to the parent business object, such as the document version, and the file interface stores the physical file location, its ownership, and its type.
Additional interfaces control more specific behavior for the files used in data sheets, data lists, and files that are persisted in the database rather than a vault.
Two file classes are delivered with a system: a template file that is persisted in the database and a general design file used to persist files in a vault. There are additional file classes for Markup files and alternate renditions, for example.