There is currently a divide in information technology research circles: on one hand, there are people working on the Semantic Web that have a very high-level vision for it. On the other hand, software engineering, which is known for its pragmatism, is largely unaware of Semantic Web technologies. In this paper, we present Hyena, an RDF-based editing platform. It makes the Semantic Web advantages available to Software Engineers without diverging too far from the concepts and tools that they are familiar with. Hyena provides editing, GUI and publishing services for implementing editors of RDF-encoded custom models. It also comes with a set of editors for many basic software engineering tasks.

We examine schema mappings from a type-theoretic perspective and aim to facilitate and formalize the reuse of mappings. Starting with the mapping language of Clio, we present a type-checking algorithm such that typeable mappings are necessarily satisfiable. We add type variables to the schema language and present a theory of polymorphism, including a sound and complete type inference algorithm and a semantic notion of a principal type of a mapping. Principal types, which intuitively correspond to the minimum amount of schema structure required by the mappings, have an important application for mapping reuse. Concretely, we show that mappings can be reused, with the same semantics, on any schemas as long as these schemas are expansions (i.e., subtypes) of the principal types.

In general, typechecking refers to the problem where, given a program P, an input type σ, and an output type τ, one must decide whether P is type-safe, that is, whether it produces only outputs of type τ when run on inputs of type σ. In the XML context, typechecking problems mainly arise in two forms: •XML-to-XML transformations, where P transforms XML documents conforming to a given type into XML documents conforming to another given type; and •XML publishing, where P transforms relational databases into XML views of these databases and it is necessary to check that all generated views conform to a specified type. A type for XML documents is typically a regular tree language, usually expressed as a schema written in a schema language such as DTD, XML Schema, or a Relax NG (see XML Types). In the XML publishing case, the input type σ is a relational database schema, possibly with integrity constraints. Typechecking problems may or may not be decidable, depending on (1) the class of programs considered, (2) the class of input types (relational schemas, DTDs, XML Schemas, Relax NG schema, or perhaps other subclasses of the regular tree languages), and (3) the class of output types. In cases where it is decidable, typechecking can be done exactly. In cases where it is undecidable, one must revert to approximate or incomplete typecheckers that may return false negatives—i.e., may reject a program even if it is type-safe. Even when exact typechecking