12. The method according to claim 11 , wherein the registering of the input-output relationship information comprises registering, with regard to an ancestor electronic document that satisfies a predetermined limiting condition among ancestor electronic documents of the second electronic document in the derivation relationship tree structure, input-output relationship information indicating that an updated electronic document to be provided in response to a document request that designates the ancestor electronic document as a requested electronic document is the second electronic document.
12. The method according to claim 11 , wherein the registering of the input-output relationship information comprises registering, with regard to an ancestor electronic document that satisfies a predetermined limiting condition among ancestor electronic documents of the second electronic document in the derivation relationship tree structure, input-output relationship information indicating that an updated electronic document to be provided in response to a document request that designates the ancestor electronic document as a requested electronic document is the second electronic document. 13. The method according to claim 12 , wherein the registering of the input-output relationship information comprises using, as the limiting condition, a condition that limits the ancestor electronic documents to an ancestor electronic document registered in the derivation relationship storage unit on time and date that is within a predetermined period from time and date when the second electronic document was registered.