One of the constraints in the flow of information is the language barrier. About half of world's literature is published in languages other than English and generally scientists would also like to know what has been published in languages with which they are not conversant (i.e., source languages). They would, therefore, need a service to get such literature translated into the languages intelligible to them (i.e., target languages).
Cover-to-cover translations are done in anticipation of use (i.e., an anticipatory service). Scientists also need translation of papers which they come across in course of literature searches. It is, therefore, necessary to develop an "on demand" translation service. The national documentation centres usually provide such service. Many special libraries and documentation centres attached to R & D establishments also have in-house translation facilities. The services of free-lance translators are also available. Depending upon the nature of the source documents and the need of scientists, three types of translation services are usually provided: