METHOD, SYSTEM AND COMPUTER PROGRAM FOR EXECUTING HOT MIGRATE OPERATION USING MIGRATION PLUG-INS
 The present application claims, under 35 U.S.C. §119, the priority benefit of European Patent Application No. 01202218.2 filed Jun. 11, 2001, the entire contents of which are herein fully incorporated by reference.
BACKGROUND OF THE INVENTION  1. Field of the Invention
 The invention relates to a method for executing a hot migrate operation through an incremental roll-over process that uses migration plug-in means for conversion during an upgrade transition, a system being arranged for implementing such a method, and a computer program implementing such a method on a carrier such as a storage medium or electrical signal.
 2. Discussion of the Related Art
 In general, during a migration or upgrading/downgrading of a service or application to a different version, the user functionality of an application will change and this change will be evident to the user. The appearance of such migration to the user has in the related art been such that either the application would be rendered inoperable or inaccessible for some time, or even worse an actually running client session would become invalidated. To the user in question, such would appear as a malfunction of the application itself or some underlying technology.
 The present inventors have recognized that in many circumstances such inoperability would be considered unacceptable and have invented the present invention which overcomes problems and limitations associated with the related art.
SUMMARY OF THE INVENTION
 The present inventors have recognized that the advantages of an incremental procedure may be able to "hide" as it were, the upgrading or migrating from user entities that are "running behind" in the migrating with respect to others that "have advanced already", and vice versa, hiding that the migration is still incomplete from user entities that have advanced already, with respect to other such entities that are still running behind. In consequence, among other things, it is an object of the present invention to keep the entries that have been converted separate from those that have not and yet to execute the migrating in a "rolling-over" manner. It is another object of the present invention to provide an application-related data repository that will remain available throughout, in particular, even during a plurality of successive sessions.
 According to one of its aspects of the invention, a method for executing a hot migrate operation from a first version of a service using a first data model, to a second version of the service using a second data model that is modified with respect to the first data model, the service comprising a client application, a data manager and a data repository, the method comprises the steps of installing at least one second version client application; installing a second version data manager operating according to the second data model; and installing a second version data
repository arranged according to the second data model and cooperating with the second version data manager, wherein the second version data manager is provided with a first migration plug-in and in that an incremental roll-over process is effectuated, and wherein in successive steps, data is converted from a first version data repository associated with the first version of the service to the second version data repository by the first migration plug-in until all data are converted and thereafter, a first version client application associated with the first version of the service becomes removable.
 In the context of the present invention, a service can represent a computer program, a database system, an operating system, an e-service, or a mixture or combination of these. Furthermore, each of these is being taken in an appropriate scope wherein it would be operative in the ambit of the hardware and software as hereinafter described by way of preferred embodiments. The context of the present invention is such where the use of the application on the one hand, and the maintaining of the application on the other, will generally be separated in time and/or in space, and/or where it would be difficult to schedule a general downtime interval for the complete system that would be sufficiently long to effect the overall migration.
 Now, the invention will hereinafter be disclosed with reference to particular embodiments. In principle however, the invention may be used on a wide scale. A particularly advantageous embodiment of the invention can be realized through the use of object-oriented programming.
BRIEF DESCRIPTION OF THE DRAWINGS
 These and further aspects and advantages of the invention will be discussed more in detail hereinafter with reference to the disclosure of preferred embodiments, and in particular with reference to the appended figures, wherein:
 FIG. 1 shows an example of two data versions in a first field of use;
 FIG. 2 shows an example of two data versions in a second field of use;
 FIG. 3 shows an example of a set-up in a third field of use;
 FIG. 4 shows a hardware embodiment for practicing the invention;
 FIG. 5 shows the design concept of the present invention according to an embodiment of the present invention;
 FIG. 6 shows, as a first UML diagram, an example of a Class diagram according to the present invention;
 FIG. 7 shows an example of an initial Version collaboration according to an embodiment of the present invention;
 FIGS. 8A and 8B show examples of collaboration during a subsequent migration according to an embodiment of the present invention;
 FIG. 9 shows an example of a final Version N+l collaboration according to an embodiment of the present invention;