The foundation of our approach is a formal representation layout knowledge. The layout knowledge is separated from the document structure and stored in a style sheet to achieve the following advantages.

• Building and maintaining a document don't require experience in layout.
• Defining layout styles guaranties a coherent layout.

A layout style consists of a set of layout primitives. These primitives are knowledge structures that meet the requirements of our processing modules; in particular these are constraints, rules and a few parameters.

Unfortunately, these primitives are sometimes hard to specify. Thus we included structures in our representation model which provide abstraction from the level of primitives. In particular these are the following ones.

Design patterns

define a scope for a set of primitives: a composition rule (basically a small document structure), an event handler and some constraints.

Design commands

encapsulate one or more design patterns. Since only one of these patterns will be applied, they enable alternative layouts. Furthermore, they serve as interface to the document structure.

Event handlers

enable a designer to react in certain events, which may occur during the layout generation.

All these structures are part of our design command language (DCL), which provides integrates procedural, Java-like code with XML-like markups. For the representation of the document structure, the design input language (DIL) has been developed. DIL is an XML subset, what means that the DC is able to interpret XHTML and XML scripts as input as well if there is an appropriate DCL style sheet.

See also the related documentation of constraints and events.