Scientists, when they read, chain document together. They reuse those chains for understanding a problem, for advancing in their research, or for writing. Systems such as Google Scholar, PubMed, Web of Knowledge, use references contained into scientific documents to link those documents together, but they are using only direct citation. More explicitly, document "a" will refer to document "b" and document "b" might refer to document "c” and those systems will create a link between these documents. But in this case “a” has a connection with “c”, but it is not explicit, therefore those systems cannot create the link. Moreover, the links between documents are not classified by type, they are generic. Users cannot know whether “a” disagree or agree with “b” without reading the document.