11. A method for providing electronic documents, comprising: registering, using a processor, when receiving an instruction to register a second electronic document that is an updated version of a first electronic document, a derivation relationship indicating that the second electronic document is derived from the first electronic document in a derivation relationship storage unit; generating, using a processor, input-output relationship information indicating an updated electronic document to be provided as an output document in response to a document request that designates a requested electronic document as an input document, based on the derivation relationship registered in the derivation relationship storage unit, and registering the input-output relationship information in an input-output relationship storage unit; when receiving a document request, obtaining, using a processor, an updated electronic document as the output document corresponding to a requested electronic document as the input document designated in the document request based on the input-output relationship information and providing the updated electronic document that is obtained; when the derivation relationship indicating that the second electronic document is derived from the first electronic document is registered in the derivation relationship storage unit, generating new input-output relationship information indicating that, with regard to each of all electronic documents that are ancestors of the second electronic document in a derivation relationship tree structure represented by derivation relationships stored in the derivation relationship storage unit, 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, and registering the generated input-output relationship information; and providing the output electronic document when a received document request designates the input document as the requested document.
11. A method for providing electronic documents, comprising: registering, using a processor, when receiving an instruction to register a second electronic document that is an updated version of a first electronic document, a derivation relationship indicating that the second electronic document is derived from the first electronic document in a derivation relationship storage unit; generating, using a processor, input-output relationship information indicating an updated electronic document to be provided as an output document in response to a document request that designates a requested electronic document as an input document, based on the derivation relationship registered in the derivation relationship storage unit, and registering the input-output relationship information in an input-output relationship storage unit; when receiving a document request, obtaining, using a processor, an updated electronic document as the output document corresponding to a requested electronic document as the input document designated in the document request based on the input-output relationship information and providing the updated electronic document that is obtained; when the derivation relationship indicating that the second electronic document is derived from the first electronic document is registered in the derivation relationship storage unit, generating new input-output relationship information indicating that, with regard to each of all electronic documents that are ancestors of the second electronic document in a derivation relationship tree structure represented by derivation relationships stored in the derivation relationship storage unit, 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, and registering the generated input-output relationship information; and providing the output electronic document when a received document request designates the input document as the requested document. 14. The method according to claim 11 , wherein the process further comprising: deleting, when first input-output relationship information is registered in the input-output relationship storage unit, second input-output relationship information in which a requested electronic document in the first input-output relationship information is an updated electronic document to be provided in accordance with the document request.