Well-Definedness and Semantic Type-Checking in the Nested Relational Calculus and XQuery

Bussche, Jan Van den; Van Gucht, Dirk; Vansummeren, Stijn

Well-Definedness and Semantic Type-Checking in the Nested Relational Calculus and XQuery

Authors

Bussche, Jan Van den

Van Gucht, Dirk

Vansummeren, Stijn

Description

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.