This volume contains the proceedings of the 21st International Conference on Logic Programming which was held in Sitges (Barcelona), Spain, from October 2nd to 5th, 2005. The conference was colocated with the International Conf- ence on ConstraintProgramming(CP 2005)and the following 6 post-conference workshops: CICLOPS 2005: Colloquium on Implementation of Constraint and Logic Programming Systems CSLP 2005: Constraint Solving and Language Processing WCB 2005: Constraint Based Methods for Bioinformatics WLPE 2005: Logic-Based Methods in Programming Environments MoVeLog 2005: Mobile Code Safety and Program Veri?cation Using C- putational Logic Tools CHR 2005: Constraint Handling Rules The conferencecoincided with a solareclipse, whichoccurredon October 3rd and was visible in Sitges. No conference activities were scheduled at the time of the eclipse to allow delegates to view this extraordinary astronomical event. Since the ?rst conference that was held in Marseilles in 1982, ICLP has been the premier international conference for presenting research in logic progr- ming. In this edition of the conference, extra attention was given to novel - plications of logic programming and to work providing novel integrations of di?erent areas. Colocation with CP 2005 further reinforced these themes, as it provided an opportunity for the exchange of ideas and cross-fertilization among two areaswhich havecommon roots. ICLP 2005and CP 2005sharedthe invited speakers to underscore this e?ort. ICLP 2005 broke new ground by holding a doctoral consortium for the ?rst time in the ICLP series of conference.

Inhalt
OWL: A Description Logic Based Ontology Language.- Preference Reasoning.- The G12 Project: Mapping Solver Independent Models to Efficient Solutions.- Use of Logic Programming for Complex Business Rules.- A Generator of Efficient Abstract Machine Implementations and Its Application to Emulator Minimization.- On the Relation Between Answer Set and SAT Procedures (or, Between cmodels and smodels).- Towards an Integration of Answer Set and Constraint Solving.- A Comparison of CLP(FD) and ASP Solutions to NP-Complete Problems.- Guard and Continuation Optimization for Occurrence Representations of CHR.- Coordination of Many Agents.- Parallelizing Union-Find in Constraint Handling Rules Using Confluence Analysis.- An Optimised Semantic Web Query Language Implementation in Prolog.- A Distributed and Probabilistic Concurrent Constraint Programming Language.- HYPROLOG: A New Logic Programming Language with Assumptions and Abduction.- Abduction of Linear Arithmetic Constraints.- Towards Implementations for Advanced Equivalence Checking in Answer-Set Programming.- Hybrid Probabilistic Logic Programs with Non-monotonic Negation.- Reducing Inductive Definitions to Propositional Satisfiability.- Symbolic Support Graph: A Space Efficient Data Structure for Incremental Tabled Evaluation.- Dynamic Mixed-Strategy Evaluation of Tabled Logic Programs.- Nondeterminism Analysis of Functional Logic Programs.- Techniques for Scaling Up Analyses Based on Pre-interpretations.- Deductive Multi-valued Model Checking.- Polynomial Interpretations as a Basis for Termination Analysis of Logic Programs.- Testing for Termination with Monotonicity Constraints.- A Well-Founded Semantics with Disjunction.- Semantics of Framed Temporal Logic Programs.- Practical Higher-Order Pattern Unification with On-the-Fly Raising.- Small Proof Witnesses for LF.- A Type System for CHR.- Decision Support for Personalization on Mobile Devices.- A Generic Framework for the Analysis and Specialization of Logic Programs.- The Need for Ancestor Resolution When Answering Queries in Horn Clause Logic.- Modeling Systems in CLP.- A Sufficient Condition for Strong Equivalence Under the Well-Founded Semantics.- IMPACT: Innovative Models for Prolog with Advanced Control and Tabling.- Using CLP to Characterise Linguistic Lattice Boundaries in a Text Mining Process.- Hybridization of Genetic Algorithms and Constraint Propagation for the BACP.- The MYDDAS Project: Using a Deductive Database for Traffic Characterization.- Open World Reasoning in Datalog.- Optimizing Queries for Heterogeneous Information Sources.- Denotational Semantics Using Horn Concurrent Transaction Logic.- Gentra4cp: A Generic Trace Format for Constraint Programming.- Analyses, Optimizations and Extensions of Constraint Handling Rules: Ph.D. Summary.- Formalization and Verification of Interaction Protocols.- -LTL for Constraint-Based Security Protocol Analysis.- Concurrent Methodologies for Global Optimization.- A Temporal Programming Language for Heterogeneous Information Systems.- Nonmonotonic Logic Programs for the Semantic Web.- ICLP 2005 Doctoral Consortium.- Analysis and Optimization of CHR Programs.