Systems for searching, indexing and cross-referencing The usefulness of a database can be increased enormously if it is easy to find entries that satisfy certain search criteria. Some examples of searches that a scientist might want to do: • All entries with the keyword "GTPase". • The entries which have a given literature reference (by author or article). • All proteins with the keyword "ribosomal" from human (organism). The databases themselves may contain this information, but some software systems must be used to actually perform this kind of search. There are different ways of designing such systems, and two examples are mentioned here. SRS The Sequence Retrieval System (SRS) developed by Thure Etzold is a system for integrating heterogenous databases . It is based on premade indexes of the items (words, entries, data fields, text,. ..) found in a set of documents (database files). Apart from the database files themselves, the indexing procedure requires a grammar (Icarus) that describes what different words in the data files mean, how they are to be
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