XML query and schema languages have some obvious connections to Formal Language Theory. For example, Document Type Definitions (DTDs) can be viewed as tree grammars and use regular expressions, XML Schemas resemble tree automata. Likewise, there are immediate links to Logic, e.g., through the classical characterization of regular tree languages by monadic second-order logic.
It is therefore not surprising that concepts from Logic and Formal Language Theory played an important role in the development of the theoretical foundations of XML query and schema languages. For example, they helped to analyze the expressiveness of languages, to understand the restrictions posed by the W3C standards, and to develop algorithms for various purposes, including efficient evaluation and static analysis.
However, methods from Logic and Formal Languages have not merely been applied to XML theory, the fertilization took place both ways. XML theory posed a lot of new challenges for Logic and Formal Language Theory and triggered various new research lines, e.g., the study of deterministic regular expressions and the development of automata for trees with data values.
The aim of the talk at FoIKS 2012 is to present some of the fundamental connections between XML query and schema languages and Logic and Formal Language Theory, to report on recent developments in the area, and to highlight some current directions of research. This accompanying paper is a kind of annotated bibliography for that talk.