Markup languages in human-computer interaction

Markup languages are increasingly used in HCI to represent relevant information and process it. Interest in them has been stimulated, in particular, by the growing availability of many potential interaction devices and the need for supporting a wide variety of users, including the disabled. Th e XML metalanguage has become the de facto standard for creating markup languages, and a variety of XML-based languages have been proposed to address various aspects relevant to HCI. A markup language is a set of words and symbols useful for identifying and describing the diff erent parts of a document. It combines text and related extra information, expressed using markup symbols intermingled with the primary text in a hierarchical structure of elements and attributes. Some reasons can be identifi ed at the basis of XML's popularity. First, diff erent from some markup languages that are purpose-specifi c (e.g., HTML for describing document appearance) and that cannot be reused for a diff erent goal, XML is a self-describing format in which the markup elements represent the information content. Th us, XML completely leaves the interpretation of such data to the application that reads them, and information content is separated from information rendering, making it easy to provide multiple views of the same data. By leaving the names, hierarchy, and meanings of elements/attributes open and defi nable, XML lays the foundation for creating custom and modular (new formats can be defi ned by combining and reusing other formats) XML-based markup languages. Also, XML has a plain text format, which means that it is both human and machine-readable. Th e wide availability of tools for text fi le authoring soft ware facilitates rapid XML document authoring and maintenance, and cross-platform interoperability. Th is was not so easy before XML's advent when most data interchange formats were proprietary "binary" formats, and therefore not easily shared by diff erent soft ware applications or across diff erent computing platforms. Moreover, the strict syntax and parsing requirements allow the appropriate parsing algorithms to remain simple, effi cient, and consistent. XML is a robust, logically verifi able format based on international standards and is unencumbered by licenses or restrictions. Lastly, it is well supported. Th us, by choosing XML, it is possible to access a large and growing community of tools, services, and technologies based on it (XLink , XPointer, XSLT, but also RDF and the semantic web). XML-based languages have been considered to address various aspects relevant to HCI. For example, as pervasive computing evolves, interactive application developers should cope with the problem of providing solutions for simultaneous deployment on a growing number of platforms for disparate users in a wide variety of contexts. Because developing ad hoc solutions might result in a signifi cant overhead, one feasible solution is abstracting from the presentation details of the specifi c medium used for the interaction, and focusing more properly on aspects related to the semantic of the interaction, namely what is the expected result that an interaction should reach. Th us, capturing and describing the essence of what a user interface should be can be obtained by identifying logical descriptions that contain semantic information and are able to highlight the main aspects to consider.