The purpose of Linked Data is to develop a total data space (the data web) able to mutually connect and enrich shared databases. Libraries therefore have the opportunity to integrate the structured information of their catalogs with information from other multiple sources and to make them more accessible by building them on web standards. The ability model the data, making them accessible and preserving the contextualization is proposed as a criterion for determining the quality of a library. The article deals with the essential articulation of semantic web and its application in the universe of libraries, and the opportunity to use shared languages, meta-languages, controlled vocabularies and ontologies that are able to meet the need for automatic processing.