Definition of SDI 

H.P. Luhn in one of this papers , published in 1961 , defined SDI Service as 'that service within an organisation which concerns itself with the channeling of new items of information, from whatever source, to those points within the organisation where the probability of usefulness in connection with current work or interests is high". SDI was developed with a specific purpose of providing a researcher at regular intervals a carefully selected list of all publications in his particular area of interest that have been published in all the significant journals of the world in the preceding interval.  

The advances in computer arid communications technology and the availability of comprehensive databases covering world literature iii machine-readable form including CD-ROM format, has greatly enhanced the potential of SDI Service and expanded its scope so that what was originally conceived as a local service for an individual research organisation, has now acquired the function of providing a national or international service.