I'm not so convinced that e-book textbooks are all that either.
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Next, I think it is going to be very hard to find things in the textbook. Unless you know exactly the word or phrase you're looking for, I think it will be faster and easier to search through a physical textbook vs. an electronic one. You'll have to finger scroll through a ton of pages vs. just flipping through a real book. I often remembered where things in my textbooks were according to what was around them. For example, I know a paragraph I want to find. I see a diagram in the text and know the paragraph was after that. Flip some more, see another diagram- oops too far. I think this process flows a lot more naturally and more quickly with a physical book than an e-book. Plus you can scan two entire pages of text at the same time. The iPad does not have sufficient resolution or screen area to do this effectively.
The iPad uses the ePub format for digital books, which is "unsuitable for publications which require precise layout or contain advanced formatting. Examples of such publications are comic books and technical books."
Modern textbooks have complicated formatting. They have detailed sections headings that can include line art, indentation, and blocks of color. They have pictures and complicated diagrams inline with the text. They often have supplemental material along the margins, including figure captions, definitions, tables, graphics, and charts. Sometimes there is an independent portion within a section that is differentiated with it's own heading and color background.
One strength eBooks have over traditional books is that links in the text can be used to reference other parts of the book. If you come across a concept from a previous section that you don't remember, you can just tap a link instead of looking it up in the index or table of contents. Unfortunately, the ePub format is poor at this too.
Another criticism of EPUB revolves around the specification's lack of detail on linking into, between, or within an EPUB book, as well as its lack of a specification for annotation. Such linking is hindered by the use of a ZIP file as the container for EPUB. Furthermore, it is unclear if it would be better to link by using EPUB's internal structural markup (the OPF specification mentioned above) or directly to files through the ZIP's file structure.[18] No standardized way to annotate EPUB books could lead to difficulty sharing and transferring annotations
Textbooks in the ePub format in the iBookstore will make for terrible textbooks.