When I first looked at e-books several years ago there was a format war going on to no very great effect. Today, as e-readers seem poised to finally go mainstream, it looks as though there are two formats that are becoming standard: pdf and epub.

These two formats are both supported by the Apple iPhone and iPod Touch; by the Sony Reader; by Barnes & Noble’s Nook ereader; and many others.

A simple comparison

Pdf files are designed to be fixed-format, so that when you create a pdf file you give it a page size. When a pdf file is viewed on a mobile phone, a pda or an e-reader, then the reader usually has to zoom in and out to see the whole page.

Epub files are designed to be fluid like most web pages. When you view an epub file on a small screen then the page will reshape itself to fit the new format.

This means that the two file formats are likely to co-exist for some time because they have different strengths and weaknesses.

If you are publishing a digital version of a novel then the fluid format may fit your needs perfectly. The novel will be readable on anything from a smartphone to a desktop pc with a huge monitor. The number of “pages” in the novel will vary but that will hardly matter at all, because whatever number of “pages” there are they will all be as readable as the hardware allows.

If you are publishing a technical manual containing a lot of detailed illustrations, then the pdf format might be much more suitable. The graphics might not make any sense if they are scaled to fit a mobile device, and the book might not make any sense without the graphics. It may be necessary, then, to insist that the number of pages (and the size of each page) remains constant whatever the device, and that people viewing the book on a mobile device scroll both horizontally and vertically to see the content of each page.

The epub format

The first thing you need to know about an epub file is that it is not actually a file. It is a zipped archive. If you take an epub file and rename it as a zip file (from book1.epub to book1.zip, for example) then you can open it with any stard archiving application.

When you open it you will find that it contains a number of html files, several xml files, and a stylesheet. These are the only components of a standard epub file. The details of the format are concerned with what each file should contain and which files should be stoed where.

Useful Links

The best place that I have found to start looking at the epub format in any depth is Web-Books.com. They have a clear non-technical guide to how the format works, as well as an online application to convert Word documents to epub format, and a set of free e-books that you can download and read.

The actual epub format is discussed in an Epub Format Construction Guide at HXA.name, which also has a range of other interesting articles.

Publishing with XML have a very useful guide to XHTML Strategies. Structures, Titles and Headers, which explains how elements should be styled.

There are also several tutorials written by Adobe, showing how you can use In-Design to create epub documents.