1. A computer-implemented method comprising: receiving, at a computer system, a user request to access an electronic document collection that integrates a plurality of electronic sub-documents that are each of one of a plurality of defined document types; retrieving information that is associated with the document collection and identifies a first sub-document of a first type of the plurality of sub-documents using a first non-address identifier that does not provide a storage location for the first sub-document; retrieving information that is associated with the document collection and identifies a second sub-document of a second type of the plurality of sub-documents using a second non-address identifier that does not provide a storage location for the second sub-document; identifying a first software application that is configured to provide access to the first sub-document; identifying a second software application that is configured to provide access to the second sub-document; initiating a connection with a server that causes execution of the identified first software application and that, using the first non-address identifier, provides access to the first sub document; initiating a connection with a server that causes execution of the identified second software application and that, using the second non-address identifier, provides access to the second sub-document; integrating access to the first sub-document into the document collection ; and integrating access to the second sub-document into the document collection; wherein at least a portion of data in the first sub-document is dynamically linked to the second sub-document using the second non-address identifier; wherein the first software application interprets the first sub-document, identifies the dynamic link and requests data from the second sub-document using the second non-address identifier; wherein the second software application receives a request for data from the second sub-document, interprets the second sub-document, and provides information relating to the requested data.
10. The computer-implemented method of claim 1 , wherein the computer system is configured to provide a stack of undo operations that is shared by the plurality of sub-documents of the document collection, wherein a plurality of software applications, each of which are configured to provide access to one or more of the plurality of sub-documents, are configured to use the stack for undo operations.