Clio grows up

TLDR

Clio is an IBM Research system that evolved from a prototype into a production mapping technology, providing declarative schema mappings between XML or relational schemas and generating XQuery, XSLT, SQL, and SQL/XML queries. This paper revisits Clio’s architecture and algorithms. Clio compiles mappings into an abstract query graph that captures transformation semantics and is serialized into appropriate query languages, with optimizations for scalability discussed.

Abstract

Clio, the IBM Research system for expressing declarative schema mappings, has progressed in the past few years from a research prototype into a technology that is behind some of IBM's mapping technology. Clio provides a declarative way of specifying schema mappings between either XML or relational schemas. Mappings are compiled into an abstract query graph representation that captures the transformation semantics of the mappings. The query graph can then be serialized into different query languages, depending on the kind of schemas and systems involved in the mapping. Clio currently produces XQuery, XSLT, SQL, and SQL/XML queries. In this paper, we revisit the architecture and algorithms behind Clio. We then discuss some implementation issues, optimizations needed for scalability, and general lessons learned in the road towards creating an industrial-strength tool.