Citation analysis is an activity and method to analyze the relationship between citation and cited literature, and it is also a discipline including the principle, method and application of citation analysis. Citation analysis is an analysis method based on the relationship between documents. Specifically, the documents in the document system are not isolated, but interrelated. The relationship between documents is highlighted in the cross-reference of documents. In the process of compiling documents, it is usually necessary to refer to relevant documents. When a document is published, the author often lists his "references" or "bibliography" in the form of endnotes or footnotes. "Citation" refers to references, the cited documents are cited, and the cited documents are accepted. When talking about the relationship between citation and citation, Price pointed out that every cited document has the references of the cited (author) and the cited (citation).

A document can be cited as well as cited. When we say citation, we can stand from two angles: first, from the perspective of cited documents, then citation is its citation; Second, from the perspective of citation, citation is citation itself. Citation is directional, and it is generally later than citation to cite documents, so it is impossible to quote backwards.

When you quote a document, you don't quote the whole content. Therefore, the cited part of literature can be called knowledge unit, and knowledge unit can be divided into generation unit and storage unit. If document A contains bibliographic notes that use and describe document B, document A contains references to document B, and document B refers to the contents of document A ... In the above process, A is called cited document and B is called cited document. According to the concept of citation relation of periodicals-knowledge production unit and knowledge storage unit (Zinkhanand Leigh, 1999), we also call A as knowledge storage unit and B as knowledge production unit (Eghi and Russo, 1992). Knowledge flows from B to A, as shown in figure 1, which shows that citation is a dynamic process.

Figure 1 refers to the concept corresponding to the process.

When there are few documents in the citation network (less than a few hundred), a citation map can be used to vividly express the citation relationship between documents. When the arrow points from the end representing di to the end representing dj, a collection of documents forms a directed graph called "citation graph" or "citation network" (Figure 2).