Résumé
The Semantic Web relies on persistent, resolvable, and negotiable URIs. However, many ontology URIs fail to meet these expectations, whether for identifying the ontologies themselves or the entities they contain. This paper presents an analysis of more than 1900 URIs from two major ontology repositories (aka. Semantic Artefact Catalogues) -AgroPortal and BioPortal-revealing that 54% of ontology URIs are not resolvable and that 92% do not support HTTP content negotiation. In response, we introduce a suite of tools and infrastructure enhancements developed within AgroPortal to diagnose and address URI management challenges at no cost for ontology developers and end users. Our approach offers a standalone diagnostic tool, the generation of "twin URIs" that support resolution and negotiation, and mechanisms to enable HTTP redirection. This system applies both to ontology URIs and to content URIs within ontologies. For the latter, our infrastructure returns -in four syntaxes-only the RDF statements directly related to the resource in question, not the complete source file. We demonstrate the entire system through the AgroPortal web interfaces and services (http://agroportal.lirmm.fr).