21. A system for analysing an input text portion and retrieving documents relevant to the text portion, the system comprising: input means for receiving an input comprising an input text portion; identification means to identify at least one text term in the text portion; assignment means for assigning at least one weight associated with the at least one text term; indexing means for forming an input local term index of the at least one text term in the input text portion and at least one associated local term weight, wherein the at least one associated local text term weights is determined with reference to a global term index stored in a database, the global term index comprising a plurality of global text terms and associated global text term weights, and being formed from a plurality of reference documents, wherein a representation of each of the reference documents is stored in the database; query means for querying the database to identify one or more relevant reference documents with respect to the input text portion; output means for outputting a representation of the identified relevant reference documents; display means for displaying the relevant reference documents on a user interface, the user interface comprising input means for receiving user input with respect to each of the displayed reference documents; user input means accepting user-input on one or more of the displayed documents; processing means for analysing the user input and re-forming the input local text term index; query means for querying the database on the basis of the re-formed input local text term index to identify one or more relevant reference documents of enhanced relevance to the input text portion; and output means for outputting a representation of the further identified reference documents of enhanced relevance.
23. The system as claimed in claim 21 wherein the re-forming of the input local term index comprises: with the processing means, forming an augmented input local term index on the basis of text terms in the local term indexes of documents receiving a positive indication of relevance; and the querying of the database on the basis of the re-formed input local text term index comprises: with the query means, querying the database on the basis of the input local text term weights in the augmented input local text term index to identify one or more relevant reference documents of enhanced relevance to the input text portion.