File Extension File Type Popularity
EPUB Open EBook Format Very popular ( 5 / 5 )

EPUB file structure


EPUB files is basically a ZIP archive. E-book readers can access such files without unpacking them. However, some interesting information can be obtained by unpacking and viewing an EPUB archive.

EPUB standard clearly describes the required elements of any EPUB file:

  1. OPS folder

  2. Mimetype file

  3. Container.xml file

OPS folder holds the book contents, such as:

  • fonts used in the publication

  • illustrations (image files)

  • formatting file (CSS stylesheet)

  • text file (HTML)

  • content.OPF file

  • toc.NCX file

OPF file is commonly referred to as content file as it contains e-book metadata. It is an XML-formatted file that describes the format of the publication (Package section). It is further divided into the following elements:

  • metadata – describes such properties as: title, ISBN, or language

  • manifest – lists all the files comprising the publication

  • spine – contains references to publication contents that are listed in the table of contents (must point to a proper toc.NCX file)

  • guide – additional content such as bibliography or list of figures.

toc.NCX file is an XML-formatted table of contents.

Mimetype file contains information necessary to identify given publication. This file is used as a base for validating given publication.

Container.xml file stored in META-INF folder point to the location of content.OPF file.