Indexing and Abstracting Services:

While the compilation and publication of an indexing and abstracting service in itself is an information service, many publishers of these services, provide a wide range of supplementary  services. One of the most important examples is the services provided by the Chemical Abstracts Service (CAS) which publishes the Chemical Abstracts, the world's most comprehensive abstracting service in chemistry and allied subject areas. Besides publishing the weekly Chemical Abstracts, it provides online access to the CA database (the online version is called CA search) and also the following supplementary services: i)  Search Service -undertakes computer searches (for those who lack the time or facilities) and provides search outputs. ii)  Selective Dissemination of Information Service.