"The concepts that characterize the DeCS vocabulary are organized in a tree structure allowing a search on broader or narrower terms or on all terms from the same tree within the hierarchical structure. DeCS is a dynamic vocabulary totaling 30,895 descriptors, of which 26,664 come from MeSH, and 4658 are exclusively DeCS. There is an addition of 2051 hierarchic codes from DeCS categories in 1491 MeSH descriptors. The following are the DeCS categories and their total number of descriptors: Health Surveillance (828); Homeopathy (1,944), Public Health (3,491); and Science and Health (219). The sum is greater than the total number of descriptors, since a descriptor may occur more than once in the hierarchy. By being dynamic, it records a permanent process of change including the development of new areas of terminology. With the creation of the national, institutional and thematic VHLs, search strategies were made available in the various topics in order to facilitate the retrieval of the existing literature. DeCS was created to serve as a unique language in indexing articles from scientific journals, books, congress proceedings, technical reports, and other types of materials, as well as for searching and retrieving subjects from scientific literature from information sources available on the Virtual Health Library (VHL) such as LILACS, MEDLINE, and others."