Distributed processing management for de-centralized information ecosystem technologies (DIET)

• US 7,805,731 B2
• Filed: 03/01/2002
• Issued: 09/28/2010
• Est. Priority Date: 03/01/2001
• Status: Expired due to Fees

• Current Assignee: British Telecommunications PLC (BT Group PLC)
• Original Assignee: British Telecommunications PLC (BT Group PLC)
• Inventors: Wang, Fang, Hoile, Cefn R, Bonsma, Erwin R, Marrow, Paul
• Primary Examiner(s): Zhen; Li B
• Application Number:
  US10/468,768
• Publication Number:
  US 20040078420A1
• Time in Patent Office: 3,133 Days
• Field of Search: 719/313, 719/317, 719/330, 709/202
• US Class Current: 719/317
• CPC Class Codes: G06F 9/468 Specific access rights for resources, e.g. using capability register
• CPC Class Codes: G06F 9/485 Task life-cycle, e.g. stopping, restarting, resuming execution G06F9/4881 takes precedence
• CPC Class Codes: G06F 9/4862 the task being a mobile agent, i.e. specifically designed to migrate
• CPC Class Codes: G06F 9/544 Buffers; Shared memory; Pipes

Abstract

A system for distributed process management uses a plurality of units of software installed on a computing platform. Further software controls operation of the plurality of units in use. Each unit of software communicates with other units of software, and at least some of the units of software further provides one or more elements of a software process. The further software being capable of defining at least one set of software units and controlling communication by the units in the set to be limited to communication only with other units of the set

Claims

1. A system for distributed process management comprising a plurality of software units comprising executable computer program code stored in a non-transitory computer-readable storage medium for installation on a computing platform, and further software for controlling the operation of the plurality of software units in use of the system, wherein:

the further software is capable of defining, for each of the computers, a plurality of environments, each environment containing a respective set of said software units and being resident only on its own computer;

each software unit is provided with means adapted for communicating with other software units by the sending and receiving of messages;

at least some of the software units are further provided with means adapted to provide one or more elements of a software process;

each such communicating means includes means storing request handling conditions and is adapted to respond to a request from its own software unit, referred to hereafter as the source unit, for the establishment of a respective connection for a particular communications session between the source unit, and another software unit, referred to hereafter as the target unit, by

determining in accordance with the request handling conditions whether it is allowed to handle the request, and if it is so allowed providing to the further software for that respective connection either a complete identity or a family identity for the target unit; and

, provided that the further software confirms that the respective environment in which the source unit is resident, currently contains a software unit corresponding to the provided identity,

constructing, via the further software, in respect of that respective connection, corresponding source and target ConnectionEnds, each of the ConnectionEnds being provided with the identity of the other of the ConnectionEnds,

providing the source unit with the identity of the newly constructed source ConnectionEnd,

providing the target unit with the identity of the newly constructed target ConnectionEnds,

obtaining, by the source unit'"'"'s communicating means from the target unit'"'"'s communicating means, the identity of the target unit, and

requesting, by the source unit'"'"'s communicating means, the target unit to accept the newly constructed target ConnectionEnd,

whereby messages from the source unit to the target unit for that particular communications session travel along a path from the source unit to the newly constructed source ConnectionEnd, and then to the newly constructed target ConnectionEnd, and then to the target unit, and in the opposite direction along that path for messages from the target unit to the source unit for that particular communications session;

wherein the corresponding ConnectionEnds are destroyed on cessation of that established communications session.

2. The system according to claim 1, wherein each of said plurality of software units is provided with an event portal having a plurality of buffers each for storing events of a respective type incoming to that software unit from initiating ones of said software units, wherein each buffer has a respective predetermined capacity for storing events and incoming events exceeding that respective capacity result in the generation of respective rejection notifications for the corresponding initiating software units, and wherein the portal is adapted to store an incoming event in the buffer corresponding to its type.

3. The system according to claim 1, wherein the means for communicating of at least one software unit is operative to translate the identity of at least its own software unit so as to hide that identity from a target unit while a connection therebetween is established.

4. The system according to claim 1, wherein the further software defines more than one said set, and wherein communication between a first said software unit, referred to hereafter as the first unit, in a first said set and a second said software unit, referred to hereafter as the second unit, in a second said set is by means of messages sent from the first unit to a said software unit in the first set and representing the second unit, referred to hereafter as the second unit representative, relayed from the second unit representative to a said software unit in the second set and representing the first unit, referred to hereafter as the first unit representative, and forwarded from the first unit representative to the second unit, and with necessary changes having been made for messages sent from the second unit to the first unit.

5. The system according to claim 4, wherein the first unit is capable of (a) requesting the further software to establish the first unit representative in the second set by creating the first unit representative initially in the first set, the first unit representative so created comprising a software process which is capable of migrating that unit from said first set to a specified said set, and (b) specifying that the first unit representative so created is to migrate to the second set.

6. The system according to claim 5, wherein the first unit representative is capable of (a) requesting the further software to establish the second unit representative in the first set by creating the second unit representative initially in the second set, the second unit representative so created comprising a software process which is capable of migrating that unit from said second set to a specified said set, and (b) specifying that the second unit representative so created is to migrate to the first set, and wherein the second unit representative is capable, when resident in the first set, of establishing a connection to the first unit.

7. The system according to claim 5, wherein the first unit representative is capable of (a) requesting the further software to establish the second unit representative in the first set by creating a said software unit in the second set, the software unit so created comprising a software process which is capable of migrating that unit to a specified said set, and (b) specifying that the software unit so created is to migrate to the first set, and, when resident in the first set, is to create the second unit representative, and wherein the second unit representative is capable of establishing a connection to the first unit.

8. The system according to claim 5, wherein:

in each said set the software units have unique local identities, and

the local identity of said first unit includes a specific family identifier identifying a function to be provided by said first unit for other software units of said first set; and

said further software is capable of creating said first unit representative such as to have either said specific family identifier or a non-specific family identifier in accordance with a specifier in said request by said first unit in dependence upon whether or not said function is to be made available to software units of said second set.

9. The system according to claim 5, wherein:

the first unit is capable of (a) requesting the further software to establish the first unit representative in the second set by creating a said software unit in the first set and (b) specifying that the software unit so created is to be the second unit representative, and that the second unit representative so created is to be capable of requesting the further software to establish the first unit representative in the second set;

the second unit representative so created is capable of requesting the further software to establish the first unit representative in the second set by creating the first unit representative initially in the first set, and wherein the first unit representative so created comprises a software process which is capable of migrating that unit from said first set to a specified said set, and wherein the first unit specifies that the first unit representative so created is to migrate to the second set, and wherein the first unit representative is capable, when resident in the second set, of establishing a connection to the second unit; and

the software process which is capable of migrating its unit to a specified set is arranged to migrate that created unit upon its creation.

10. The system according to claim 5 wherein:

the first unit is capable of (a) requesting the further software to establish the first unit representative in the second set by creating a said software unit in the first set and (b) specifying that the software unit so created is to be the second unit representative, and that the second unit representative so created is to be capable of requesting the further software to establish the first unit representative in the second set;

the second unit representative so created is capable of requesting the further software to establish the first unit representative in the second set by creating the first unit representative initially in the first set, and wherein the first unit representative so created comprises a software process which is capable of migrating that unit from said first set to a specified said set, and wherein the first unit specifies that the first unit representative so created is to migrate to the second set, and wherein the first unit representative is capable, when resident in the second set, of establishing a connection to the second unit; and

the software process which is capable of migrating its unit to a specified set is arranged to migrate that created unit upon receipt of a migration command.

11. The system according to claim 5, wherein at least one ConnectionEnd of said corresponding source and target ConnectionEnds has a reference to a transaction state.

12. The system according to claim 4, wherein the first unit is capable of (a) requesting the further software to establish the first unit representative in the second set by creating a said software unit in the first set, the software unit so created comprising a said migrating process which is capable of migrating that unit to a specified said set, and (b) specifying that the software unit so created is to migrate to the second set and, when resident in the second set, is to create the first unit representative.

13. The system according to claim 4, wherein the first unit is capable of (a) requesting the further software to establish the first unit representative in the second set by creating a said software unit in the first set and (b) specifying that the software unit so created is to be the second unit representative, and that the second unit representative so created is to be capable of requesting the further software to establish the first unit representative in the second set.

14. The system according to claim 13, wherein the second unit representative so created is capable of requesting the further software to establish the first unit representative in the second set by creating the first unit representative initially in the first set, and wherein the first unit representative so created comprises a software process which is capable of migrating that unit from said first set to a specified said set, and wherein the first unit specifies that the first unit representative so created is to migrate to the second set, and wherein the first unit representative is capable, when resident in the second set, of establishing a connection to the second unit.

15. The system according to claim 13, wherein the second unit representative so created is capable of (a) requesting the further software to establish the first unit representative in the second set by creating a said software unit in the first set, the software unit so created comprising a software process which is capable of migrating that unit to a specified said set, and (b) specifying that the software unit so created is to migrate to the second set and, when resident in the second set, is to create the first unit representative, and wherein the first unit representative is capable of establishing a connection to the second unit.

16. The system according to claim 13, wherein:

in each said set the software units have unique identities, and

the local identity of said second unit includes a specific family identifier identifying a function to be provided by said second unit for other software units of said second set; and

said further software is capable of creating said second unit representative such as to have either said specific family identifier or a non-specific family identifier in accordance with a specifier in said request by said first unit in dependence upon whether or not said function is to be made available to software units of said first set.

17. The system according to claim 1, wherein the request handling conditions include a maximum for the number of current connections that the source unit is allowed to have.

18. The system according to claim 1, wherein each of the newly constructed source and target ConnectionEnds include means storing state information relating to the respective connection for that particular communications session, and each of the source and target units is adapted to respond to receipt of a message of that particular connection by retrieving from its ConnectionEnd the stored state information and determining therefrom a required action.

19. A computing platform installed in a computing environment including at least one computer to support the running of a software process by use of processing and data storage capacity of the computing environment, the platform having installed thereon a system according to claim 1, and comprising means for creating said software units, and software support means for maintaining a plurality of units of processing capacity of the computing environment for allocation to selected software units during running of a said software process.

20. The platform according to claim 19 wherein each software unit has an associated resource account mechanism which subtracts resources from the account when the software unit makes requests of the further software and adds resources to the account when the software unit performs specified actions successfully.

21. An applications platform installed in a computing environment including at least one computer to support the running of an application by use of processing and data storage capacity of the computing environment, the installed platform comprising:

means to create a first community of software units; and

means to provide a support software environment to the first community,

wherein an application to be run on the platform is installed as processes of a selected plurality of the first community of software units, and processes for support of the application in use are themselves installed on further software units of the first community;

wherein a first unit maintained in the first community is capable of (a) requesting the further software to establish the first unit representative in a second community of units by creating the first unit representative initially in the first community, the first unit representative so created comprising a software process which is capable of migrating that unit from said first community to a specified other community and (b) specifying that the first unit representative so created is to migrate to the second community while also leaving said first unit to be maintained in said first community,

wherein, similarly, a second unit maintained in the second community is capable of (a) requesting the further software to establish a second unit representative in the first community of units by creating the second unit representative initially in the second community, the second unit representative so created comprising a software process which is capable of migrating that unit from said second community to a specified other community and (b) specifying that the second unit representative so created is to migrate to the first community while also leaving said second unit to be maintained in said second community,

wherein a respective connection for a particular communications session between the first unit and the second unit is established by the creation of a pair of ConnectionEnds in the first community for communications between the first unit and the second unit representative, and a pair of ConnectionEnds in the second community for communications between the second unit and the first unit representative, and the creation of respective carrier units which transport messages between the unit representatives, and

wherein the means to provide a support software environment to the community maintains a plurality of units of processing capacity of the computing environment for allocation to selected units of the community of software units during running of an application.

22. The platform according to claim 21, wherein the number of units of processing capacity is less than the number of software units in the community.

23. The platform according to claim 21, wherein said plurality has a maximum number which is determined when an application is first started.

24. The platform according to claim 21, wherein each software unit is arranged such that, regardless of whether or not it is currently allocated a unit of processing capacity of the computing environment, communication therewith can be initiated by another software unit.

25. The platform according to claim 24, wherein each software unit is provided with means to maintain state information in relation to a communication with another software unit and each software unit maintains that state information whether or not it is currently allocated a unit of processing capacity of the computing environment.

26. The platform according to claim 25, wherein each said software unit includes at least one dedicated software unit maintains at least one element of data relevant to its associated software unit.

27. The platform according to claim 26, wherein one element of data maintained by a dedicated software unit is the state information in relation to a communication with another software unit.

28. The platform according to claim 26, wherein one element of data maintained by a dedicated software unit provides a measure of success of the software unit to which it is dedicated, said measure of success being a factor in replication or destruction of the software unit such that the community is capable of adaptation.

29. The platform according to claim 25, wherein if an event requires that a software unit be allocated a unit of processing capacity and that software unit is not currently allocated a unit of processing capacity, the computing environment will automatically allocate that software unit an available unit of processing capacity.

30. The platform according to claim 25, wherein if an event requires that a software unit be allocated a unit of processing capacity, that software unit is not currently allocated a unit of processing capacity, and the computing environment does not have a unit of processing capacity available for allocation, that event is rejected by the software unit.

31. The platform according to claim 25, wherein the support software environment is further adapted to support destruction of software units of the community.

32. The platform according to claim 21, wherein each software unit in a community is provided with a portal provided with means to store event data in relation to events yet to be processed by the software unit.

33. The platform according to claim 32, wherein said event data includes a count of events yet to be processed.

34. The platform according to claim 33, wherein the portal maintains a maximum in relation to the count of events yet to be processed, any incoming event being rejected once the count has reached its maximum.

35. The platform according to claim 34, wherein the portal maintains multiple counts of events in different type categories, and a maximum for each of said multiple counts.

36. A system for distributed process management comprising a plurality of software units comprising executable computer program code stored in a non-transitory computer-readable storage medium for installation on a computing platform comprising a plurality of interconnected computers, and further software for controlling the operation of the software units in use of the system, wherein:

the further software is capable of defining, for each of the computers, a plurality of environments, each environment containing a respective set of said software units and being resident only on its own computer;

each software unit is provided with means adapted for communicating with other software units by the sending and receiving of messages;

at least some of the software units are further provided with means adapted to provide one or more elements of a software process;

each such communicating means includes means storing request handling conditions and is adapted to respond to a request from its own software unit, referred to hereafter as the source unit, for the establishment of a respective connection for a particular communications session between the source unit, and another software unit, referred to hereafter as the target unit, by

determining in accordance with the request handling conditions whether it is allowed to handle the request, and if it is so allowed providing to the further software for that respective connection either a complete identity or a family identity for the target unit; and

, provided that the further software confirms that the respective software environment in which the source unit is resident, currently contains a software unit corresponding to the provided identity,

constructing, via the further software, in respect of that respective connection, corresponding source and target ConnectionEnds, each of the ConnectionEnds being provided with the identity of the other of the ConnectionEnds, and

providing the source unit with the identity of the newly constructed source ConnectionEnd and providing the target unit with the identity of the newly constructed target ConnectionEnd whereby messages from the source unit to the target unit for that particular communications session travel along a path from the source unit to the newly constructed source ConnectionEnd, and then to the newly constructed target ConnectionEnd, and then to the target unit, and in the opposite direction along that path for messages from the target unit to the source unit for that particular communications session;

wherein the corresponding ConnectionEnds are destroyed on cessation of that established communications session;

wherein the further software defines more than one said set, and wherein communication between a first said software unit, referred to hereafter as the first unit, in a first said set and a second said software unit, referred to hereafter as the second unit, in a second said set is by means of messages sent from the first unit to a said software unit in the first set and representing the second unit, referred to hereafter as the second unit representative, relayed from the second unit representative to a said software unit in the second set and representing the first unit, referred to hereafter as the first unit representative, and forwarded from the first unit representative to the second unit, and with necessary changes having been made for messages sent from the second unit to the first unit;

wherein the first unit is capable of (a) requesting the further software to establish the first unit representative in the second set by creating the first unit representative initially in the first set, the first unit representative so created comprising a software process which is capable of migrating that unit from said first set to a specified said set, and (b) specifying that the first unit representative so created is to migrate to the second set; and

wherein in each said set the units of software have unique local identities and the first unit representative is capable of (a) requesting the further software to establish the second unit representative in the first set by creating the second unit representative initially in the second set, the second unit representative so created comprising a software process which is capable of migrating that unit from said second set to a specified said set, and (b) specifying that the second unit representative so created is to migrate to the first set, and wherein the second unit representative is capable, when resident in the first set, of establishing a connection to the first unit, and

the local identity of said second unit includes a specific family identifier identifying a function to be provided by said second unit for other software units of said second set; and

said further software is capable of creating said second unit representative such as to have either said specific family identifier or a non-specific family identifier in accordance with a specifier in said request by said first unit representative in dependence upon whether or not said function is to be made available to software units of said first set.

37. The system according to claim 36, wherein the first unit is capable of (a) requesting the further software to establish the first unit representative in the second set by creating a said software unit in the first set and (b) specifying that the software unit so created is to be the second unit representative, and that the second unit representative so created is to be capable of requesting the further software to establish the first unit representative in the second set.

38. The system according to claim 36, wherein the second unit representative so created is capable of requesting the further software to establish the first unit representative in the second set by creating the first unit representative initially in the first set, and wherein the first unit representative so created comprises a software process which is capable of migrating that unit from said first set to a specified said set, and wherein the first unit specifies that the first unit representative so created is to migrate to the second set, and wherein the first unit representative is capable, when resident in the second set, of establishing a connection to the second unit.

39. The system according to claim 36, wherein the second unit representative so created is capable of (a) requesting the further software to establish the first unit representative in the second set by creating a said software unit in the first set, the software unit so created comprising a software process which is capable of migrating that unit to a specified said set, and (b) specifying that the software unit so created is to migrate to the second set and, when resident in the second set, is to create the first unit representative, and wherein the first unit representative is capable of establishing a connection to the second unit.

40. The system according to claim 36, wherein:

in each said set the software units have unique local identities, and

the local identity of said first unit includes a specific family identifier identifying a function to be provided by said first unit for other software units of said first set; and

said further software is capable of creating said first unit representative such as to have either said specific family identifier or a non-specific family identifier in accordance with a specifier in said request by said first unit in dependence upon whether or not said function is to be made available to software units of said second set.

41. A system for distributed process management comprising a plurality of software units comprising executable computer program code stored in a non-transitory computer-readable storage medium for installation on a computing platform comprising a plurality of interconnected computers, and further software for controlling the operation of the software units in use of the system, wherein:

the further software is capable of defining, for each of the computers, a plurality of environments, each environment containing a respective set of said software units and being resident only on its own computer;

each software unit is provided with means adapted for communicating with other software units by the sending and receiving of messages;

at least some of the software units are further provided with means adapted to provide one or more elements of a software process;

each such communicating means includes means storing request handling conditions and is adapted to respond to a request from its own software unit, referred to hereafter as the source unit, for the establishment of a respective connection for a particular communications session between the source unit, and another software unit, referred to hereafter as the target unit, by

determining in accordance with the request handling conditions whether it is allowed to handle the request, and if it is so allowed providing to the further software for that respective connection either a complete identity or a family identity for the target unit; and

, provided that the further software confirms that the respective software environment in which the source unit is resident, currently contains a software unit corresponding to the provided identity,

constructing, via the further software, in respect of that respective connection, corresponding source and target ConnectionEnds, each of the ConnectionEnds being provided with the identity of the other of the ConnectionEnds, and

providing the source unit with the identity of the newly constructed source ConnectionEnd and providing the target unit with the identity of the newly constructed target ConnectionEnd whereby messages from the source unit to the target unit for that particular communications session travel along a path from the source unit to the newly constructed source ConnectionEnd, and then to the newly constructed target ConnectionEnd, and then to the target unit, and in the opposite direction along that path for messages from the target unit to the source unit for that particular communications session;

wherein the corresponding ConnectionEnds are destroyed on cessation of that established communications session;

wherein the further software defines more than one said set, and wherein communication between a first said software unit, referred to hereafter as the first unit, in a first said set and a second said software unit, referred to hereafter as the second unit, in a second said set is by means of messages sent from the first unit to a said software unit in the first set and representing the second unit, referred to hereafter as the second unit representative, relayed from the second unit representative to a said software unit in the second set and representing the first unit, referred to hereafter as the first unit representative, and forwarded from the first unit representative to the second unit, and with necessary changes having been made for messages sent from the second unit to the first unit;

wherein the first unit is capable of (a) requesting the further software to establish the first unit representative in the second set by creating the first unit representative initially in the first set, the first unit representative so created comprising a software process which is capable of migrating that unit from said first set to a specified said set, and (b) specifying that the first unit representative so created is to migrate to the second set; and

wherein each of said unit representatives is capable of (a) requesting the further software to create a software unit, referred to hereafter as a carrier unit, the said carrier unit so created being capable of carrying a said message and comprising a software process which is capable of migrating that unit to a specified said set, and (b) specifying that the carrier unit so created is to migrate to the set of the other of said unit representatives, connect to the other of said unit representatives and deliver the carried message.

42. The system according to claim 41, wherein a said carrier unit is capable of reuse for carrying a message in the reverse direction.

43. A system for distributed process management comprising a plurality of software units comprising executable computer program code stored in a non-transitory computer-readable storage medium for installation on a computing platform comprising a plurality of interconnected computers, and further software for controlling the operation of the software units in use of the system, wherein:

the further software is capable of defining, for each of the computers, a plurality of environments, each environment containing a respective set of said software units and being resident only on its own computer;

each software unit is provided with means adapted for communicating with other software units by the sending and receiving of messages;

at least some of the software units are further provided with means adapted to provide one or more elements of a software process;

each such communicating means includes means storing request handling conditions and is adapted to respond to a request from its own software unit, referred to hereafter as the source unit, for the establishment of a respective connection for a particular communications session between the source unit, and another software unit, referred to hereafter as the target unit, by

determining in accordance with the request handling conditions whether it is allowed to handle the request, and if it is so allowed providing to the further software for that respective connection either a complete identity or a family identity for the target unit; and

, provided that the further software confirms that the respective software environment in which the source unit is resident, currently contains a software unit corresponding to the provided identity,

constructing, via the further software, in respect of that respective connection, corresponding source and target ConnectionEnds, each of the ConnectionEnds being provided with the identity of the other of the ConnectionEnds, and

providing the source unit with the identity of the newly constructed source ConnectionEnd and providing the target unit with the identity of the newly constructed target ConnectionEnd whereby messages from the source unit to the target unit for that particular communications session travel along a path from the source unit to the newly constructed source ConnectionEnd, and then to the newly constructed target ConnectionEnd, and then to the target unit, and in the opposite direction along that path for messages from the target unit to the source unit for that particular communications session;

wherein the corresponding ConnectionEnds are destroyed on cessation of that established communications session;

wherein the further software defines more than one said set, and wherein communication between a first said software unit, referred to hereafter as the first unit, in a first said set and a second said software unit, referred to hereafter as the second unit, in a second said set is by means of messages sent from the first unit to a said software unit in the first set and representing the second unit, referred to hereafter as the second unit representative, relayed from the second unit representative to a said software unit in the second set and representing the first unit, referred to hereafter as the first unit representative, and forwarded from the first unit representative to the second unit, and with necessary changes having been made for messages sent from the second unit to the first unit;

wherein the first unit is capable of (a) requesting the further software to establish the first unit representative in the second set by creating the first unit representative initially in the first set, the first unit representative so created comprising a software process which is capable of migrating that unit from said first set to a specified said set, and (b) specifying that the first unit representative so created is to migrate to the second set;

wherein the first unit representative is capable of (a) requesting the further software to establish the second unit representative in the first set by creating the second unit representative initially in the second set, the second unit representative so created comprising a software process which is capable of migrating that unit from said second set to a specified said set, and (b) specifying that the second unit representative so created is to migrate to the first set, and wherein the second unit representative is capable, when resident in the first set, of establishing a connection to the first unit;

wherein each of said unit representatives is capable of (a) requesting the further software to create a software unit, referred to hereafter as a carrier unit, the said carrier unit so created being capable of carrying a said message and comprising a software process which is capable of migrating that unit to a specified said set, and (b) specifying that the carrier unit so created is to migrate to the set of the other of said unit representatives, connect to the other of said unit representatives and deliver the carried message, and

wherein a said unit representative, so created and capable of requesting the further software to establish the other of said unit representatives, is further capable of (a) requesting the further software to create directly or indirectly said other of said unit representatives to be capable of requesting the further software to create the said carrier unit to have an identifier specific to the said unit representative, and of (b) requesting the further software to create a said carrier unit to have said specific identifier, and wherein each of said unit representatives is capable of determining the future handling of a message received via a carrier unit in dependence upon whether or not that carrier unit has said specific identifier.

44. The system according to claim 43, wherein the first unit is capable of (a) requesting the further software to establish the first unit representative in the second set by creating a said software unit in the first set, the software unit so created comprising a said migrating process which is capable of migrating that unit to a specified said set, and (b) specifying that the software unit so created is to migrate to the second set and, when resident in the second set, is to create the first unit representative.