Editor's note: Juergen Boos is director of the Frankfurt Book Fair. He gives us his views on the development of the e-book market.

We should view the success of e-books in the US market by acknowledging that the country has a unique approach to royalty payments, marketing and technology and customer habits. Moreover, in the US, romantic novels in e-book form have extremely good sales and outstrip any other type of literature. That's because of the demographic, whereby women aged 20 to 40 are the main consumers of e-books. So, despite the high sales in the US, the country should not be taken as a benchmark to evaluate the maturity of the world's e-book markets. For example, Germany is the world's third-largest market after the US and the UK, but sales accounted for just 1 percent of total domestic book sales in 2011.

Cultural differences are one of the main factors affecting the development of e-books. One of the reasons Japan is falling behind is that the country has no specified format and can't decide whether to use the horizontal or vertical version. In Brazil, e-readers are not popular because people prefer to read on their cell or smartphones.

Ultimately, successful development will depend on how children use these digital products, because they will decide the future of digital publishing. It is a decisive role. I know that China is now promoting the e-bag - an e-book package for schoolchildren that is used in place of traditional textbooks and learning materials - and I think that's a very good thing. When children get used to the e-reading or e-bag experience, they will feel comfortable using digital books.

Juergen Boos was speaking to Zhang Yuchen.