Transforming a set of biological flat file librariesto a fast access network

SRS (Sequence Retrieval System), an indexing system for flatfile libraries, provides fast access to individual library entriesvia retrie by keywords from rious data fields. SRS is now alsoable to build indices using cross–references that mostlibraries provide. Fifteen libraries of DNA and protein sequencesand structures have been selected. These libraries interactwith at least one other by means of cross–references.Indexing these cross–references allows a complete networkof libraries to be built. In the network an entry from one librarycan be linked in principle to every other library. If two librariesare not directly cross–referenced, the linkage can bemade with a succession of single links between neighbouring,cross–referenced libraries. A new operator has been addedto the query language of SRS for convenient specification oflinks amongst complete libraries or entry sets generated byprevious queries on particular libraries. All the informationin the network can now be used to retrieve an entry in a specificlibrary, e.g. the full information given in amino acid sequenceentries from SwissProt can now be used to retrieve related tertiarystructure entries from PDB. Furthermore, a search in a singlelibrary can be extended to a search in the complete librarynetwork, e.g. all entries in all databases pertaining to elastasecan be found.