Visual Composition of XPath Expressions for External Metadata Authoring

Web metadata is crucial for providing a machine-understandable descriptions on Web resources, and has a number of applications such as discovery, qualification, and adaptation of Web contents. While metadata is often embedded into a target document, metadata can also be associated externally by means of an addressing scheme such as the XPath language. However, creation and modification of external metadata would not be easy solely with a conventional editor because metadata authoring involves the maintenance and elaboration of the addressing expressions as well as editing individual documents. The objective of this study is to pursue extensibility in the design of annotation editors with particular emphasis on the visual composition of XPath expressions. The key idea behind the XPath composer is to facilitate flexibility in the creation of XPath expression as results of the seamless integration of three composition methods: instantaneous creation, selective customization, and full customization. In this paper, we introduce a framework of external annotation first, and give a high-level overview of an annotation editor. The three composition methods are then explained, showing examples of XPath expressions and the graphical user interface for the visual composition. Finally, we present an annotation editor developed with the XPath composer, and show how the annotation editor is customized for an annotation vocabulary at hand.