In this section, several different kinds of user interfaces are described, including
natural-language interfaces, question-and-answer interfaces, menus, form-fill interfaces,
command-language interfaces, graphical user interfaces (GUIs), and a variety
of Web interfaces for use on the Internet. The user interface has two main components:
presentation language, which is the computer-to-human part of the transaction,
and action language, which characterizes the human-to-computer portion.
Together, both concepts cover the form and content of the term user interface.