19. A computer program product comprising a non-transitory computer useable storage medium including a computer readable program, wherein the computer readable program when executed on a computer causes the computer to: calculate the total importance of each of electronic documents, on the basis of (i) a plurality of electronic documents, chained to each other in a relation of referencing and being referenced, from a start electronic document which is not referenced by any other electronic document to a terminal electronic document which does not reference any other document, (ii) information on relation of referencing and being referenced, (iii) a first phrase, and (iv) a second phrase, (i) through (iv) being stored in a storage device, the computer program including instructions to cause a computer to: (a) calculate the importance unique to one electronic document of a given electronic document among the plurality of electronic documents, on the basis of the degree of similarity between the first phrase and a phrase included in the given electronic document, and by sequentially applying an equation to pairs of the plurality of the electronic documents; (b) identify at least one second electronic document which references the given electronic document, on the basis of the information on relation of referencing and being referenced; (c) calculate a response coefficient against a first electronic document, on the basis of the degree of similarity between a phrase included in the second electronic document and the second phrase; (d) calculate the total importance of the given electronic document, on the basis of the importance unique to one electronic document of the given electronic document and total importance of the second electronic document; and (e) calculate the total importance of each of the plurality of electronic documents, by performing (a) through (d) on each pair of the plurality of electronic documents.
19. A computer program product comprising a non-transitory computer useable storage medium including a computer readable program, wherein the computer readable program when executed on a computer causes the computer to: calculate the total importance of each of electronic documents, on the basis of (i) a plurality of electronic documents, chained to each other in a relation of referencing and being referenced, from a start electronic document which is not referenced by any other electronic document to a terminal electronic document which does not reference any other document, (ii) information on relation of referencing and being referenced, (iii) a first phrase, and (iv) a second phrase, (i) through (iv) being stored in a storage device, the computer program including instructions to cause a computer to: (a) calculate the importance unique to one electronic document of a given electronic document among the plurality of electronic documents, on the basis of the degree of similarity between the first phrase and a phrase included in the given electronic document, and by sequentially applying an equation to pairs of the plurality of the electronic documents; (b) identify at least one second electronic document which references the given electronic document, on the basis of the information on relation of referencing and being referenced; (c) calculate a response coefficient against a first electronic document, on the basis of the degree of similarity between a phrase included in the second electronic document and the second phrase; (d) calculate the total importance of the given electronic document, on the basis of the importance unique to one electronic document of the given electronic document and total importance of the second electronic document; and (e) calculate the total importance of each of the plurality of electronic documents, by performing (a) through (d) on each pair of the plurality of electronic documents. 20. The computer program product of claim 19 , including: sequentially applying the equation c i =s i +a×r ij ×c j to pairs of the plurality of the electronic documents.