14. An apparatus to determine a document rank, the apparatus comprising: a processor, a term relationship score calculating unit, a term relationship score changing unit, a contribution score calculating unit, and a document rank score calculating unit, the processor to control the term relationship score calculating unit, the term relationship score changing unit, the contribution score calculating unit, and the document rank score calculating unit, wherein the term relationship score calculating unit is configured to calculate a first term relationship score of a first document and a second term relationship score, and wherein the contribution score calculating unit is configured to calculate a first contribution score based on a common keyword between the first document and a second document, the second document being linked by a link to the first document, wherein the term relationship score changing unit is configured to change the first term relationship score to the second term relationship score, wherein the document rank score calculating unit is configured to calculate a document rank score of the second document based on the first term relationship score and the first contribution score, and to update the document rank score of the second document based on the second term relationship score, wherein the first term relationship score is determined based on content of the first document and the link, and wherein the processor is further configured to determine whether each of a plurality of contribution scores is greater than a predetermined threshold value to update the document rank score, whereby if one of the contribution scores is less than or equal to the predetermined threshold value, that contribution score is set to a zero value.
19. The apparatus of claim 14 , wherein: the term relationship score changing unit is configured to change the first term relationship score to the second term relationship score in response to deletion of the link; and the first term relationship score comprises a term relationship score with respect to the common keyword of the content of the first document.