8. A method for finding documents which are closely related to a subject, by using other keywords along with chosen keywords, in the case where a same document is referred to by multiple documents and by multiple keywords, the method comprising: extracting citation context of each document, that cites at least one document, in a database containing documents, the citation context is determined as a text in a window of predetermined size around a citation marker in a citing document, wherein the citation context is determined as a text around the citation marker inside the window; identifying meaningful keywords from the citation context of the citing document for each cited document; forming a citation network, wherein the citing document and the cited documents form nodes of the citation network, a first node corresponding to the citing document is connected to all the nodes corresponding to the cited documents forming edges of the citation network, wherein each edge of the citation network is labelled with an inferred keyword, the inferred keyword is an identified meaningful keyword from the citation context of the citing document corresponding to the cited document forming the edge; constructing a table T comprising sets of the citing document, the cited document, and the inferred keywords in the citation, receiving keywords from a user to initiate a search, inferring terms which are similar to the keywords, identifying the citing and cited documents in the table T by searching the keywords and the inferred similar terms in the table T, forming a relating document pool for all results in the table T corresponding to both the keywords and the inferred similar terms, ranking the documents of the relating document pool by using a graph based ranking algorithm running on citation networks of the set of the keywords and the similar terms.
8. A method for finding documents which are closely related to a subject, by using other keywords along with chosen keywords, in the case where a same document is referred to by multiple documents and by multiple keywords, the method comprising: extracting citation context of each document, that cites at least one document, in a database containing documents, the citation context is determined as a text in a window of predetermined size around a citation marker in a citing document, wherein the citation context is determined as a text around the citation marker inside the window; identifying meaningful keywords from the citation context of the citing document for each cited document; forming a citation network, wherein the citing document and the cited documents form nodes of the citation network, a first node corresponding to the citing document is connected to all the nodes corresponding to the cited documents forming edges of the citation network, wherein each edge of the citation network is labelled with an inferred keyword, the inferred keyword is an identified meaningful keyword from the citation context of the citing document corresponding to the cited document forming the edge; constructing a table T comprising sets of the citing document, the cited document, and the inferred keywords in the citation, receiving keywords from a user to initiate a search, inferring terms which are similar to the keywords, identifying the citing and cited documents in the table T by searching the keywords and the inferred similar terms in the table T, forming a relating document pool for all results in the table T corresponding to both the keywords and the inferred similar terms, ranking the documents of the relating document pool by using a graph based ranking algorithm running on citation networks of the set of the keywords and the similar terms. 9. The method of claim 8 , wherein in the step of “inferring terms which are similar to the keywords”, the terms which are similar to the keywords are terms that are frequently used together with the keywords in the citations.