ePub ebook Format Explained

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I spend a lot of time writing about the virtues of the ePub format on this blog. But I’ve never gone into detail about what ePub is and why it’s an important ebook format. I realize there are still a lot of newbies joining the ebook world and they may not be familiar with the the basic formats.

To start with, ePub is short for ‘electronic publication’ and is the standard format adopted by the International Digital Publishing Forum. Because ePub is an open-source format, it’s free to use. With the proper technical-knowledge and some basic design skills, anyone can create an ePub formatted ebook using a software program like Adobe InDesign.

The main benefit of ePub is that it’s an open-source format. Like I said above, this means anyone can create an ebook in the ePub format so there’s no need to pay third-party licensing fees, purchasing special software or deal with proprietary formats that are closed systems.

ePub Structure

The basic structure of ePub is pretty straightforward and divided into three parts:

XHTML Documents: The main content of your ebook is in XHTML. This allows your ebook to be easily formatted for reading on a number of devices.

Packaging Files: These files keep everything organized. Packaging files can be divided into two main parts; the .OPF file and the .NCX file. In a nutshell, the .OPF file contains all the basic information about your ebook including title, author, publisher, etc. The .NCX file is your ebook’s organization by telling the file the sequence of chapters, parts and so forth.

Container Files: The only real purpose of container files is for those evil publishers who insist on locking their ebooks with Digital Rights Management (DRM). If the ebook is DRM-free, then the container file is only a few lines of basic code. That’s about all I know about container files.

The three components above are then wrapped up in a nice package into a ZIP file. Pretty easy, huh? I got all the above information from web-books.com in their ePub section.

Supported Devices

Because of ePub’s simple and easy-to-use format, a lot of major ebook reader manufacturers are adopting ePub as the official format for their devices. Most notably are the Sony family of ebook readers and the new Barnes & Noble Nook. Other devices that support ePub are the Kobo eReader, iRex, COOL-ER, BeBook, etc.

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