MLA

Hempel, and Thomas Hempel. Usability of Speech Dialog Systems. Springer Berlin Heidelberg, 2008.

APA

Hempel, H., & Hempel, T. (2008). Usability of Speech Dialog Systems. Springer Berlin Heidelberg.

Chicago

Hempel, and Thomas Hempel. Usability of Speech Dialog Systems. : Springer Berlin Heidelberg, 2008.