Simple bundling formats. These formats encapsulate their constituent files and, save for a directory that provides the filenames, do not describe the content and the relationships that may obtain between files. (In this, they differ from what are often called wrappers.) Archetypes include ZIP, StuffIt, and TAR, the latter associated with the UNIX operating system. Simple bundling formats tend to be generic, i.e., they may be used for a wide range of content types.
The OEBPS Container Format (OCF) is a format that employs ZIP but implements it in a manner that shares features with the self-describing bundling formats discussed below, another indicator of the lack of sharp boundaries between subcategories.
Self-describing bundling formats. These formats are employed to represent the bundle of files that comprise a complex digital work, e.g., a book text with supporting illustrations or a movie with multiple segments and sound tracks in different languages. Self-describing bundling formats list the component parts and their relationships (information about the relationships is often called structural metadata) and may indicate how the work as a whole can be rendered or used. Bundling formats often incorporate technical details about each component, since a single object may include a mix of texts, sound, images, etc. They may or may not encapsulate their constituent files. They include metadata that describes their content and the relationships between files. Archetypes for this subcategory include METS (Metadata Encoding and Transmission Standard) and MPEG-21 (Multimedia Framework).
Some examples of self-describing bundling formats are intentionally generic. MPEG-21 has been designed, in the words of the MPEG standard's working group, to support content producers and consumers as they "exchange, consume, trade, and otherwise manipulate digital items in an efficient, transparent, and interoperable way." Meanwhile, some bundling formats have been proposed for more specific purposes or communities. For example, DTB (the Digital Talking Book Format) has a more constrained structure for a specific purpose.
This definition is taken from the introduction (Formats, Evaluation Factors, and Relationships) to the Sustainable Digital Formats Web site.