The arrival of the 21st century coincides with an explosion in the volume of digital information. This overabundance of information calls for new methods and models capable of extracting information from a jumble of poorly structured knowledge.
Electronic" metadata is information about digital objects (image, text, sound) that describes their content, management, structure, context and access conditions. Metadata, used extensively by documentation professionals, can already facilitate access to certain archived documents. However, the use of ontologies, for organizing and structuring knowledge, is starting to gain ground in order to obtain "smarter" information, applied to certain fields (legal, medical, educational, etc.).
After a few reminders of the traditional use of metadata in heritage archives and libraries, the use of metadata is analyzed in the context of the Web. Particular emphasis is placed on the description of XML-based technologies, which play a fundamental role both in describing information and in processing it. The final section looks at new solutions for making metadata machine-readable, including the prospects offered by the use of ontologies.