Libraries have always been treasuries of well-organized, easily accessed knowledge. Tools used for that purpose - library catalogs, systems for content description and structured metadata - are extremely valuable in the case of traditional libraries storing non-virtual, non-digital publications. When the content is put in the digital form, the tools in question become ineffective and, very often, useless to many library users. It results from the fact that contemporary full-text search and retrieval systems enable users to obtain information not only from the descriptions but also from the entire content of the documents. It means that all effort put into the construction and development of controlled library catalogs may soon become unnecessary.