Information Processing Letters
ACM Transactions on Information Systems (TOIS)
Foundations of Databases: The Logical Level
Foundations of Databases: The Logical Level
Conjunctive Query Containment Revisited
ICDT '97 Proceedings of the 6th International Conference on Database Theory
Reformulation of XML Queries and Constraints
ICDT '03 Proceedings of the 9th International Conference on Database Theory
Structural Properties of XPath Fragments
ICDT '03 Proceedings of the 9th International Conference on Database Theory
Monadic Queries over Tree-Structured Data
LICS '02 Proceedings of the 17th Annual IEEE Symposium on Logic in Computer Science
Visual Web Information Extraction with Lixto
Proceedings of the 27th International Conference on Very Large Data Bases
On the Exponent of Periodicity of Minimal Solutions of Context Equation
RTA '98 Proceedings of the 9th International Conference on Rewriting Techniques and Applications
The complexity of XPath query evaluation
Proceedings of the twenty-second ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Optimal implementation of conjunctive queries in relational data bases
STOC '77 Proceedings of the ninth annual ACM symposium on Theory of computing
The complexity of satisfiability problems
STOC '78 Proceedings of the tenth annual ACM symposium on Theory of computing
Constraint Processing
Monadic datalog and the expressive power of languages for Web information extraction
Journal of the ACM (JACM)
D-theory: talking about talking about trees
ACL '83 Proceedings of the 21st annual meeting on Association for Computational Linguistics
A new algorithm for normal dominance constraints
SODA '04 Proceedings of the fifteenth annual ACM-SIAM symposium on Discrete algorithms
Theory of Relational Databases
Theory of Relational Databases
Efficient algorithms for processing XPath queries
VLDB '02 Proceedings of the 28th international conference on Very Large Data Bases
MARS: a system for publishing XML from mixed and redundant storage
VLDB '03 Proceedings of the 29th international conference on Very large data bases - Volume 29
Logic-based web information extraction
ACM SIGMOD Record
The Lixto data extraction project: back and forth between theory and practice
PODS '04 Proceedings of the twenty-third ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
XML data exchange: consistency and query answering
Proceedings of the twenty-fourth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Rewriting XPath queries using materialized views
VLDB '05 Proceedings of the 31st international conference on Very large data bases
Semantic characterizations of navigational XPath
ACM SIGMOD Record
Exploiting native XML indexing techniques for XML retrieval in relational database systems
Proceedings of the 7th annual ACM international workshop on Web information and data management
ACM Transactions on Database Systems (TODS) - Special Issue: SIGMOD/PODS 2004
Conjunctive queries over trees
Journal of the ACM (JACM)
Efficient evaluation of n-ary conjunctive queries over trees and graphs
WIDM '06 Proceedings of the 8th annual ACM international workshop on Web information and data management
Dominance constraints in stratified context unification
Information Processing Letters
Journal of Computer and System Sciences
XML transformation by tree-walking transducers with invisible pebbles
Proceedings of the twenty-sixth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
The complexity of query containment in expressive fragments of XPath 2.0
Proceedings of the twenty-sixth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Evaluation of datalog extended with an XPath predicate
Proceedings of the 9th annual ACM international workshop on Web information and data management
Navigational XPath: calculus and algebra
ACM SIGMOD Record
Data Complexity of Query Answering in Expressive Description Logics via Tableaux
Journal of Automated Reasoning
Using a relational processor and an XPath processor to evaluate joint queries
DataX '08 Proceedings of the 2008 EDBT workshop on Database technologies for handling XML information on the web
ACM Computing Surveys (CSUR)
From XQuery to relational logics
ACM Transactions on Database Systems (TODS)
Journal of Logic, Language and Information
Automated interaction in social networks with datalog
CIKM '10 Proceedings of the 19th ACM international conference on Information and knowledge management
Satisfiability of XPath queries with sibling axes
DBPL'05 Proceedings of the 10th international conference on Database Programming Languages
Matching with regular constraints
LPAR'05 Proceedings of the 12th international conference on Logic for Programming, Artificial Intelligence, and Reasoning
Logics for unranked trees: an overview
ICALP'05 Proceedings of the 32nd international conference on Automata, Languages and Programming
First order paths in ordered trees
ICDT'05 Proceedings of the 10th international conference on Database Theory
XSym'05 Proceedings of the Third international conference on Database and XML Technologies
Logic wrappers and XSLT transformations for tuples extraction from HTML
XSym'05 Proceedings of the Third international conference on Database and XML Technologies
On the query evaluation in document DBs
DEXA'06 Proceedings of the 17th international conference on Database and Expert Systems Applications
NGITS'06 Proceedings of the 6th international conference on Next Generation Information Technologies and Systems
Hi-index | 0.00 |
We study the complexity and expressive power of conjunctive queries over unranked labeled trees, where the tree structure are represented using "axis relations" such as "child", "descendant", and "following" (we consider a superset of the XPath axes) as well as unary relations for node labels. (Cyclic) conjunctive queries over trees occur in a wide range of data management scenarios related to XML, the Web, and computational linguistics. We establish a framework for characterizing structures representing trees for which conjunctive queries can be evaluated efficiently. Then we completely chart the tractability frontier of the problem for our axis relations, i.e., we find all subset maximal sets of axes for which query evaluation is in polynomial time. All polynomial-time results are obtained immediately using the proof techniques from our framework. Finally, we study the expressiveness of conjunctive queries over trees and compare it to the expressive power of fragments of XPath. We show that for each conjunctive query, there is an equivalent acyclic positive query (i.e., a set of acyclic conjunctive queries), but that in general this query is not of polynomial size.