Deciding equivalence of finite tree automata
SIAM Journal on Computing
DTD inference for views of XML data
PODS '00 Proceedings of the nineteenth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Normal form algorithms for extended context-free grammars
Theoretical Computer Science
Introduction To Automata Theory, Languages, And Computation
Introduction To Automata Theory, Languages, And Computation
Everything You Ever Wanted to Know About DTDs, But Were Afraid to Ask (Extended Abstract)
Selected papers from the Third International Workshop WebDB 2000 on The World Wide Web and Databases
Taxonomy of XML schema languages using formal language theory
ACM Transactions on Internet Technology (TOIT)
Expressiveness and complexity of XML Schema
ACM Transactions on Database Systems (TODS)
On the minimization of XML Schemas and tree automata for unranked trees
Journal of Computer and System Sciences
Simple off the shelf abstractions for XML schema
ACM SIGMOD Record
Inferring XML schema definitions from XML data
VLDB '07 Proceedings of the 33rd international conference on Very large data bases
Simplifying XML schema: effortless handling of nondeterministic regular expressions
Proceedings of the 2009 ACM SIGMOD International Conference on Management of data
Complexity of Decision Problems for XML Schemas and Chain Regular Expressions
SIAM Journal on Computing
CSL'07/EACSL'07 Proceedings of the 21st international conference, and Proceedings of the 16th annuall conference on Computer Science Logic
Generating, sampling and counting subclasses of regular tree languages
Proceedings of the 14th International Conference on Database Theory
Proceedings of the 20th ACM international conference on Information and knowledge management
Foundations of regular expressions in XML schema languages and SPARQL
PhD '12 Proceedings of the on SIGMOD/PODS 2012 PhD Symposium
Deciding twig-definability of node selecting tree automata
Proceedings of the 15th International Conference on Database Theory
Finding optimal probabilistic generators for XML collections
Proceedings of the 15th International Conference on Database Theory
Bounded repairability for regular tree languages
Proceedings of the 15th International Conference on Database Theory
Descriptional complexity of deterministic regular expressions
MFCS'12 Proceedings of the 37th international conference on Mathematical Foundations of Computer Science
Web Semantics: Science, Services and Agents on the World Wide Web
Conservative type extensions for XML data
Transactions on Large-Scale Data- and Knowledge-centered systems IX
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XML Schema Definitions (XSDs) can be adequately abstracted by the single-type regular tree languages. It is well-known, that these form a strict subclass of the robust class of regular unranked tree languages. Sadly, in this respect, XSDs are not closed under the basic operations of union and set difference, complicating important tasks in schema integration and evolution. The purpose of this paper is to investigate how the union and difference of two XSDs can be approximated within the framework of single-type regular tree languages. We consider both optimal lower and upper approximations. We also address the more general question of how to approximate an arbitrary regular tree language by an XSD and consider the complexity of associated decision problems.