3. The document providing system according to claim 2 , wherein said input-output relationship registration unit uses, as the limiting condition, a condition that limits the ancestor electronic documents to an ancestor electronic document registered in said derivation relationship storage unit on time and date that is within a predetermined period from time and date when the second electronic document is registered.
2. The document providing system according to claim 1 , wherein said input-output relationship registration unit registers, 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 corresponding to a document request that designates the ancestor electronic document as a requested electronic document is the second electronic document.