Term Truncation 

Term truncation is one of the devices adapted to facilitate retrieval of terms with a common root containing common fragments. Incorporation of truncation device makes it possible to search for a portion Of the term only. There are three methods of truncation: i) the beginning of the term-left truncation, ii) at the end of term-right truncation, iii) simultaneous right and left truncation. By left truncation, the term will be retrieved with the substitution of any prefix. By right truncation, the term will be retrieved with any suffix. Simultaneous left and right truncation allows simultaneous substitution of prefix and suffix to a term fragment or term root. Truncation enables retrieval of references with singular or plural forms, different tenses, etc. The usefulness of simultaneous left and right truncation can he illustrated with the following example, if a user is interested in some specified correlation's, the truncated term polymers where the star (*) indicates truncation will retrieve polymers, polymerisation, etc., whereas the left truncation (* polymers) will retrieve; copolymers, etc. Thus, it may be said that the truncation device is a very helpful tool that enables the user great facilities to search for word stems as and when the nature of the query demands. 

Two types of logic is used in the formulation of search strategy. They are Boolean approach and Weighted approach. Boolean logic utilises the operators AND, OR and. NOT, while suitable weights are assigned to the search terms of the profile so that the search result may be made more relevant to the requirement of the query formulated by the user and as perfected by the information specialist. This technique is also commonly used in SDI Systems to improve the system performance. For example let us consider a query: 

MARC (5) COMPUTER (4) CATALOGUE (1) ORDER (I) ACQUISITION (I) and suppose the threshold weight for the system is set at 5, then items including MARC (5) COMPUTER CATALOGUE (4+1), COMPUTER ACQUISITION (4+1), etc., would be retrieved. However, items including computer (4) order, acquisition (1+1) and so on would not be retrieved. This technique will naturally enhance relevancy factor and leads to better results in so far as user satisfaction is concerned. 

Notification of SDI and Feedback analysis forms the most important aspect of SDI service. The user's evaluation of SDI output results give information as to what extent the search terms or the logic that have been used have retrieved relevant or irrelevant information. An active interest and personal contact between the user and the information specialist is of great importance to reach a fast convergence for the modifications of the profiles. This enables the profiles being checked and adjusted on the basis of users' evaluation.