2. EPUB Books
EPUB books are the ebooks in the EPUB format, which was intended to be a standard ebook format. Unfortunately, more than ten years since its inception in September 2007, the format is still far from a world standard. Currently, the best selling ebooks by Amazon do not use the EPUB format. In its newest version, EPUB 3, advanced features such as MathML has been specified. However, implementation of this feature by ebook readers (viewers) is not a simple matter. To date, even the Amazon's Kindle Reader still cannot render MathML codes into mathematical equations. They resolve to use images for equations. This is not only inconvenient, but also increase ebook file size dramatically.
The EPUB format has reached a dilemma. If we want to make an EPUB book, should we use the old EPUB2 that lacks advanced features (math, interactive and multimedia), or the new EPUB3 that no applications can get it right? The failure of EPUB3 has forced Apple's iBooks to use a proprietary iBook format (IBA) for advanced features.
Another drawback of the EPUB book is that it is essentially a zip file. Anyone can unzip the book file and see all underlying contents unless encrypted. Then, to decrypt contents would cause inconvenience to users.