|The EPUB format is an
open eBook format recommended by The International Digital
Publishing Forum. It is essentially a ZIP format. If you change its
extension ".epub" to ".zip", the EPUB file becomes a true ZIP file
which can be unzipped.
The unzipped EPUB files may be divided into three categories: XHTML
documents, packaging files and container files.
XHTML Documents. XHTML is a strict version of HTML. The stricter
syntax enables web browsers or eBook viewers to render the document
more easily. This is important for reading eBooks on devices with
limited computing power such as cell phones. In an EPUB book, the
main content is placed in these XHTML documents, which can have
.html, .xhtml or .xml extension. We prefer the .html extension
because it can be viewed by most web browsers on various computing
Packaging Files. They include two files: one with the .opf extension
and another with the .ncx extension. The .opf file contains book
information (author, publisher, etc.) and a list of all files in the
book package. The .ncx file tells the sequence and organization
(parts, chapters or sections) of XHTML documents in a book.
Container Files. They must be placed in a folder named "META-INF".
These files are used for encryption and digital rights management (DRM).
For an eBook without DRM, the container file has only a few standard
Currently, the EPUB format can be viewed by
Calibre, Adobe Digital
Stanza, Aldiko and a few others. Calibre
renders CSS and table of contents very well, but it cannot highlight
or annotate. ADE has the highlighting and annotation features.
However, scrolling is not smooth when there are images or tables.
Another problem is that the table cannot be centered and content may
be lost for a long table. For instance, our Complete Poems by E. A.
Poe can be displayed perfectly by Calibre, but a lot of contents are
missing by ADE.
Calibre cannot run on any smartphone or any device with limited
computing power because it is a huge program. ADE requires Flash
Player which is not available on any smartphone yet (see Steve Jobs'
open letter). At present, you may use Stanza to read EPUB books on
iPhones or Aldiko on Android-operated devices. Apple's iPad tablet
also supports the EPUB format. It contains a native EPUB viewer
(called iBooks) and accepts 3rd-party applications for reading EPUB
books. iBooks is also available on iPhone 4
Creating EPUB Books
A number of software tools are designed for making EPUB books, such
as Adobe's InDesign or Calibre. Our web-based platform can help you
convert Word to EPUB. It also includes an HTML editor for revising
converted documents. The HTML editor is as easy to use as a regular
word processor. You can even use the editor to write a book from
Free EPUB Books
Google has more than 500,000 public domain titles in the EPUB format
and Project Gutenberg has over 20,000 titles. Our collection is
relatively small (~ 1300 titles), but they have included essentially
all popular classic books. An advantage of our EPUB books is that
they all have correct hierarchical table of contents. Our eBooks are
not limited to old books. Many of them are compiled and edited from
contemporary sources such as U.S. National Institute of Health and
Wikipedia. Some of them are original works submitted by users like
you. We are also converting the professionally developed textbooks
at Flat World Knowledge from their online version into the EPUB
format (see An Innovative Business Model All Students Love).
Digital Rights Management
The most serious drawback of the EPUB format is its lack of a
standard digital rights management (DRM), which is used to protect
ebooks from pirating. Standard DRM is virtually impossible. A
proprietary DRM can be cracked, let alone a "standard" one. Some
companies (e.g., Adobe and Apple) apply their own DRM to the EPUB
books. Then, it loses the "open" nature of the EPUB format. The
DRMed EPUB books can be read only by the EPUB viewer designed by the
company who created these DRMed EPUB books. If you bought ebooks
from Apple, you can read them only on iPad and iPhone 4. Adobe is
trying to make their ADE work on as many platforms as possible. This
will increase the cost and contribute to the high price of ebooks.
For paid ebooks, there is a need for DRM. The best solution seems to
design web-based viewers to read ebooks, such as our Web books.