In this paper, we investigate the issues that arise when binding statically typed languages to XML data. In particular, our motivation is to exploit the computational facilities of mainstream languages when computing over real-world entities encoded as XML documents or document fragments. These include completeness, strong typing, effciency, as well as user-base and support. We first show that standard binding solutions, such as the SAX and DOM APIs, do not preserve the semantics of such entities, and thus hinder program specification, verification, and optimisation. We then compare two novel approaches, which rely on type information to preserve semantics. The first is Sun's JAXB architecture, in which types are automatically generated from document descriptions. The second is our SNAQue architecture, where types are directly specified by binding computations. For certain classes of applications, we show that the latter offers substantial advantages in terms of simplicity and flexibility. In previous work [4, 8], we have formally proven that SNAQue bindings can be correctly built for a representative, canonical language. Here, we extend that work and present SNAQue/J, a binding mechanism specific to the Java language.

We take the term X/O impedance mismatch to describe the difficulty of the OO paradigm to accommodate XML processing by means of recasting it to typed OO programming. In particular, given XML types (say, XML schemas), it is notoriously difficult to map them automatically to object types (say, object models) that (i) reasonably compare to native object types typically devised by OO developers; (ii) fully preserve the intent of the original XML types; (iii) fully support round-tripping of arbitrary, valid XML data; and (iv) provide a general and convenient programming model for XML data hosted by objects. We reveal the X/O impedance mismatch in particular detail. That is, we survey the relevant differences between XML and objects in terms of their data models and their type systems. In this process, we systematically record and assess Xto-O mapping options. Our illustrations employ XSD (1.0) as the XML-schema language of choice and C# (1.0–3.0) as the bound of OO language expressiveness.

Abstract. This paper gives an overview of XML formal models, summarizes database engineering practices, problems and their evolution. We focus on categorical aspects of XML formal models. Many formal models such as XML Data Model, XQuery Data Model or Algebra for XML can be described in terms of category theory. This kind of description allows to consider generic properties of these formalisms, e.g. expressive power, optimization, reduction or translation between them, among others. These properties are rather crucial to comparison of different XML formal models and to consequent decision which formal system should be used to solve a concrete problem. This work aim is to be the basis for further research in the area of XML formal models where category theory is applied. 1