The software in an IR system enables the following operations;
- Entry of bibliographic data including index terms and the generation of the document description and index files;
- Updating of the document and index files when new documents enter the IR System or when changes are made in the existing records;
- Search of the index files by specified parameters, and the provision of search output to satisfy an information request
- Storage of user profiles and the batch searching of the file of new documents to provide regular SDI outputs to the users of the system; and
- Updating of the thesaurus file as and when new terms or new relationships are added to the vocabulary.
Since all the above mentioned operations are crucial to the performance of the IR system, software assumes an added significance.
The search software is perhaps the most important component of the IR System so far as the user is concerned. It is the search software that distinguishes manual IR Systems from computer-based IR Systems. It enables the user to search the database from several parameters, often not possible in manual systems. The main capabilities of search software may be stated as:
- Search of the database by different specified parameters such as index terms, class numbers, authors and author affiliations, journal titles, coder!, ISSN, year of publication, type of document, etc.
- In addition to the keys mentioned above, the search software enables free-text searching.
Free-text searching in combination with controlled vocabulary has been found to be the most effective way of searching large databases.
Search software also facilitates the use of term truncation in searching for information. For example, a search by the word stem compu* (the indicates truncation) will retrieve information on computer, computers, computational, computability, etc. Some search software permit only right truncation while others permit both left and right truncation. Truncation facility may be used in any search parameters. Most of the computer-based IR Systems allow search formulations with Boolean operators AND, OR, and NOT. With the aid of these operators it is possible to specify complex search requirements. For example, consider the expression: (PULSES OR CHICPEA* OR ARIETTNUM) AND (DROUGHT* OR WATER STRESS) The above search expression would retrieve information on drought, drought tolerance, drought stress or water stress in pulses, information on pulses in general or in chickpeas. The search software uses the Boolean expression to retrieve all references which satisfy the given expression. Thus, it may be noted that the capability of the search software to combine subject parameters with non-subject parameters, and the possibility of term truncation and free-text searching in different fields of the document file, and the representation of search formulation as a Boolean expression enables the performance of complex searches in large databases. This is the reason why great importance is attached to the development of search software in an IR system.