Principles of programming with complex objects and collection types
ICDT '92 Selected papers of the fourth international conference on Database theory
Deciding containment for queries with complex objects (extended abstract)
PODS '97 Proceedings of the sixteenth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems
Typechecking for XML transformers
PODS '00 Proceedings of the nineteenth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Foundations of Databases: The Logical Level
Foundations of Databases: The Logical Level
Typechecking Top-Down Uniform Unranked Tree Transducers
ICDT '03 Proceedings of the 9th International Conference on Database Theory
Typechecking for Semistructured Data
DBPL '01 Revised Papers from the 8th International Workshop on Database Programming Languages
Declarative specification of Web sites with S
The VLDB Journal — The International Journal on Very Large Data Bases
Typechecking XML views of relational databases
ACM Transactions on Computational Logic (TOCL)
XML with data values: typechecking revisited
Journal of Computer and System Sciences - Special issu on PODS 2001
Querying nested collections
Frontiers of tractability for typechecking simple XML transformations
PODS '04 Proceedings of the twenty-third ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Deciding well-definedness of XQuery fragments
Proceedings of the twenty-fourth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Polymorphic type inference for the named nested relational calculus
ACM Transactions on Computational Logic (TOCL)
Annotated XML: queries and provenance
Proceedings of the twenty-seventh ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Structural recursion on ordered trees and list-based complex objects
ICDT'07 Proceedings of the 11th international conference on Database Theory
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Two natural decision problems regarding the XML query language XQuery are well-definedness and semantic type-checking. We study these problems in the setting of a relational fragment of XQuery. We show that well-definedness and semantic type-checking are undecidable, even in the positive-existential case. Nevertheless, for a “pure” variant of XQuery, in which no identification is made between an item and the singleton containing that item, the problems become decidable. We also consider the analogous problems in the setting of the nested relational calculus.