Structural Recursion on Ordered Trees and List-Based Complex Objects
| Autor: | Stijn Vansummeren, Dirk Van Gucht, Lawrence V. Saxton, Edward L. Robertson |
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| Jazyk: | angličtina |
| Rok vydání: | 2007 |
| Předmět: |
Tree (data structure)
Theoretical computer science Computer science structural recursion nested relational calculus XQuery intrinsic computational complexity polynomial time Left recursion Computer science Primitive recursive function Recursion (computer science) Query language Mutual recursion Time complexity Computer Science::Databases Undecidable problem |
| Zdroj: | Lecture Notes in Computer Science ISBN: 9783540692690 ICDT |
| Popis: | XML query languages need to provide some mechanism to inspect and manipulate nodes at all levels of an input tree. In this paper we investigate the expressive power provided in this regard by structural recursion. We show that the combination of vertical recursion down a tree combined with horizontal recursion across a list of trees gives rise to a robust class of transformations: it captures the class of all primitive recursive queries. Since queries are expected to be computable in at most polynomial time for all practical purposes, we next identify a restriction of structural recursion that captures the polynomial time queries. Although this restriction is semantical in nature, and therefore undecidable, we provide an effective syntax. We also give corresponding results for list-based complex objects. |
| Databáze: | OpenAIRE |
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