This book constitutes the refereed proceedings of the First European Semantic Web Symposium, ESWS 2004, held in Heraklion, Crete, Greece in May 2004.The 33 revised full papers presented were carefully reviewed and selected from 79 submissions.

Ontology Engineering.- Towards On-the-Fly Ontology Construction – Focusing on Ontology Quality Improvement.- OntoEdit Empowering SWAP: a Case Study in Supporting DIstributed, Loosely-Controlled and evolvInG Engineering of oNTologies (DILIGENT).- A Protégé Plug-In for Ontology Extraction from Text Based on Linguistic Analysis.- Ontology Matching and Mapping.- Formal Support for Representing and Automating Semantic Interoperability.- S-Match: an Algorithm and an Implementation of Semantic Matching.- Ontology Mapping – An Integrated Approach.- Ontology-Based Querying.- Application of Ontology Techniques to View-Based Semantic Search and Browsing.- Active Ontologies for Data Source Queries.- Ontology Merging and Population.- Knowledge Discovery in an Agents Environment.- The HCONE Approach to Ontology Merging.- Question Answering Towards Automatic Augmentations of Ontology Instances.- Infrastructure.- The SCAM Framework: Helping Semantic Web Applications to Store and Access Metadata.- Publish/Subscribe for RDF-based P2P Networks.- Streaming OWL DL.- Semantic Web Services.- Mathematics on the (Semantic) NET.- Approaches to Semantic Web Services: an Overview and Comparisons.- OWL-S Semantics of Security Web Services: a Case Study.- Service Discovery and Composition.- Directory Services for Incremental Service Integration.- A Framework for Automated Service Composition in Service-Oriented Architectures.- Reusing Petri Nets Through the Semantic Web.- Data for the Semantic Web.- Methods for Porting Resources to the Semantic Web.- Learning to Harvest Information for the Semantic Web.- Reverse Engineering of Relational Databases to Ontologies.- Knowledge Representation.- No Registration Needed: How to Use Declarative Policies and Negotiation to Access Sensitive Resources onthe Semantic Web.- Semantic Annotation Support in the Absence of Consensus.- Uncertainty in Knowledge Provenance.- Applications.- Collaborative Semantic Web Browsing with Magpie.- Toward a Framework for Semantic Organizational Information Portal.- CS AKTiveSpace: Building a Semantic Web Application.- Content Management.- Cultural Heritage and the Semantic Web.- Neptuno: Semantic Web Technologies for a Digital Newspaper Archive.- Information Management and Integration.- MIKSI – A Semantic and Service Oriented Integration Platform.- Semantic Web Technologies for Economic and Financial Information Management.