Programmers confront a minefield when they design interactive Web programs. Web interactions take place via Web browsers. With browsers, consumers can whimsically navigate among the various stages of a dialog and can thus confuse the most sophisticated corporate Web sites. In turn, Web services can fault in frustrating and inexplicable ways. The quickening transition from Web scripts to Web services lends these problems immediacy.

Transformation of XML documents is often supported by special purpose languages that make use of pattern matching and replacement. Many XML programmers need to learn and understand one of these languages for transformation purposes. In this paper we contrast and compare special purpose, pattern matching solutions with transformation programs written in a general purpose, functional programming language. We use Scheme and the LAML libraries for XML transformations. Our approach is minimalistic in the sense that only a small vocabulary is needed to carry out the transformations. Overall, we have found that the Scheme/LAML solution is doing well in a direct comparison with other solutions. We have also found that the integrated validation of both the source and target documents makes it easier to write trustworthy transformations. A DTD-guided pruning of document traversals is also a contribution of the research.

Categories and Subject Descriptors D.1.1 [Functional Programming]: Scheme, XML 1. INTRODUCTION XML [4] is a meta language, which is used to define high-level markup languages for a variety of different purposes. As for other high-level languages (such as high-level programming languages) there is a need to transform XML documents1 to lower-level languages. Often, but not necessarily, the target language is another XML language, such as XHTML [5]. Transformation of XML documents is of interest to the programming language community in general [24], and to the functional programming community in particular. A Haskell combinator library represent early work in the area [25].

By imposing a single hierarchy on data, XML makes queries brittle in the sense that a query might fail to produce the desired result if it is executed on the same data organized in a different hierarchy, or if the hierarchy evolves during the lifetime of an application. This paper presents a new XML query language, called Morph, which supports more flexible querying. Morph is a shape polymorphic query language, that is, a single query can extract relevant data from a variety of differently hierarchies. The Morph data model distills an XML data collection into a graph of closest relationships. This paper describes the syntax, semantics, and a prototype implementation of Morph.