This volume contains papers selected for presentation at the 31st Annual C- ference on Current Trends in Theory and Practice of Informatics ¿ SOFSEM 2005, held on January 22¿28, 2005 in LiptovskyJ ¿ an, ¿ Slovakia. The series of SOFSEM conferences, organized alternately in the Czech - public and Slovakia since 1974, has a well-established tradition. The SOFSEM conferences were originally intended to break the Iron Curtain in scienti?c - change. After the velvet revolution SOFSEM changed to a regular broad-scope international conference. Nowadays, SOFSEM is focused each year on selected aspects of informatics. This year the conference was organized into four tracks, each of them complemented by two invited talks: ¿ Foundations of Computer Science (Track Chair: Bernadette Charron-Bost) ¿ Modeling and Searching Data in the Web-Era (Track Chair: Peter Vojt¿ a? s) ¿ Software Engineering (Track Chair: M¿ aria Bielikova) ¿ ¿ Graph Drawing (Track Chair: Ondrej Syk ¿ ora) The aim of SOFSEM 2005 was, as always, to promote cooperation among professionalsfromacademiaandindustryworkinginvariousareasofinformatics. Each track was complemented by two invited talks. The SOFSEM 2005 Program Committee members coming from 13 countries evaluated 144 submissions (128 contributed papers and 16 student research - rum papers). After a careful review process (counting at least 3 reviews per paper), followed by detailed discussions in the PC, and a co-chairs meeting held on October 8, 2005 in Bratislava, Slovakia, 44 papers (overall acceptance rate 34.

Invited Talks.- Discovering Treewidth.- From Research Prototypes to Industrial Strength Open Source Products - The ObjectWeb Experience.- How Hard Is It to Take a Snapshot?.- Logical Foundations for Data Integration.- Recent Advances in Graph Drawing.- The Hyperdatabase Network - New Middleware for Searching and Maintaining the Information Space.- Architecture of a Business Framework for the .NET Platform and Open Source Environments.- Progress on Crossing Number Problems.- Full Contributed Papers.- Greedy Differential Approximations for Min Set Cover.- A Methodology of Visual Modeling Language Evaluation.- Local Computations on Closed Unlabelled Edges: The Election Problem and the Naming Problem.- A Hierarchical Markovian Mining Approach for Favorite Navigation Patterns.- Non-planar Orthogonal Drawings with Fixed Topology.- A Topology-Driven Approach to the Design of Web Meta-search Clustering Engines.- Computing Upward Planar Drawings Using Switch-Regularity Heuristics.- Serial and Parallel Multilevel Graph Partitioning Using Fixed Centers.- Two-Layer Planarization: Improving on Parameterized Algorithmics.- On the Stability of Approximation for Hamiltonian Path Problems.- Robustness of Composed Timed Systems.- Topology Generation for Web Communities Modeling.- Recursion Versus Replication in Simple Cryptographic Protocols.- Modeling Data Integration with Updateable Object Views.- Fixed-Parameter Tractable Algorithms for Testing Upward Planarity.- Read/Write Based Fast-Path Transformation for FCFS Mutual Exclusion.- Adjustment of Indirect Association Rules for the Web.- Anonymous Communication with On-line and Off-line Onion Encoding.- Characteristic Patterns for LTL.- Planar Straight-Line Drawing in an Grid with Angular Resolution (1/n).- Modeling NestedRelationships in XML Documents Using Relational Databases.- RAQ: A Range-Queriable Distributed Data Structure.- On Some Weighted Satisfiability and Graph Problems.- On the Security and Composability of the One Time Pad.- Lower Bounds on the OBDD Size of Graphs of Some Popular Functions.- XML-Based Declarative Access Control.- VCD: A Visual Formalism for Specification of Heterogeneous Software Architectures.- Cost-Constrained Minimum-Delay Multicasting.- Ontology-Based Inconsistency Management of Software Requirements Specifications.- The Best Student Paper.- Suffix Tree Based Data Compression.- Short Contributed Papers.- Tier Aspect Model Based on Updatable Views.- Well-Founded Metamodeling for Model-Driven Architecture.- Stepwise Optimization Method for k-CNN Search for Location-Based Service.- An Approach for Integrating Analysis Patterns and Feature Diagrams into Model Driven Architecture.- Outerplanar Crossing Numbers of 3-Row Meshes, Halin Graphs and Complete p-Partite Graphs.- Fast Bit-Vector Algorithms for Approximate String Matching Under Indel Distance.- Feature Selection by Reordering.- A Management Scheme for the Basic Types in High Level Languages.- Bayesian Networks in Software Maintenance Management.- A Multiagent System Aiding Information Retrieval in Internet Using Consensus Methods.- Interval-Valued Data Structures and Their Application to e-Learning.- Boolean Functions with a Low Polynomial Degree and Quantum Query Algorithms.- Representation of Extended RBAC Model Using UML Language.- A Methodology for Writing Class Contracts.- Volumes of 3D Drawings of Homogenous Product Graphs.