Abstract:
A method for operating a telecommunications network is explained. A network element ( 16 ) at a network node of the telecommunications network is controlled by a control computer ( 36 ). The control computer ( 16 ) is maintained from a service computer ( 24 ). Allomorphy is taken into account in the development of application programs ( 102, 104 ) so that even a service computer ( 24 ) which is not developed can maintain the control computer ( 36 ). Making allowance for allomorphy results in little additional expenditure because an interface program ( 100 ) is used in which essential processing steps are carried out for all the application programs ( 102, 104 ), said processing steps ensuring that allomorphy is taken into consideration.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method for operating a telecommunications network, in which a network element at a network node of the telecommunications network is controlled by a control computer. The network element is, for example, a switching office for switching links, what is referred to as a cross-connector or a concentrator unit for connecting a number of subscribers to a connecting line. In addition to the operating system for operating the control computer, a number of application programs, during whose execution application objects are processed, are stored in the control computer. The application objects are associated with data with a predefined data structure and preferably also predefined methods for processing the data. The data structure and the methods are dependent on a class which is also to be specified when the respective application object is generated. A link via which the control computer is maintained via maintenance messages is set up between a service computer and a control computer. 
     Such methods are used for controlling the telecommunications network if, for example, a new switching device is to be put into operation as a network element or if subscriber data in the switching device have to be changed at a later date, such as is the case when new subscribers are connected or when an existing subscriber moves. Efficient methods for controlling the telecommunications network are obtained if what are referred to as open systems are used which are programmed in compliance with standards which apply worldwide. For example, standards of the ISO (International Standardization Organization) and of the ITU (International Telecommunication Union) with its body the ITU-T, known earlier as the CCITT (International Telegraph and Telephone Consultative Committee) relate to the setting up of such open systems. A separate control network is to be used to control the telecommunications network. The interfaces between the service computer and switching device are standardized in protocols Q 1 , Q 2  and Q 3 . 
     The application objects are defined as objects of an object-oriented language, for example in the language C++ or CHILL. If the application programs are developed, it is necessary to ensure that the control network also operates without faults with the new application programs. As such, in particular, application objects which are considered by the service computer as belonging to an original class cannot readily be assigned to an amended alternative class. 
     This problem is mentioned in the CCITT standard X.720 (01/92)—“Information Technology—Open Systems Interconnection—Structure of Management Information: Management Information Model”—in the section 5.2.1. In the section 5.2.3 of the standard X.720, two methods for solving the problem are proposed. In the first method, on the part of the application program, a programming technique is used which takes allomorphy into consideration. Allomorphy is the ability of a specific application object of the alternative class to be controlled as if it were an object of the original class if this ability arises as a result of measures on the part of the application program. The other method includes taking measures on the part of the service computer which permit cooperation between the service computer and the application program even when the application program is developed. 
     European patent application EP-A-0 817 422 discloses a method for implementing controlled objects in a subsystem of a controlled system in a network, at least one control system and one controlled system being present. The controlled objects are implemented independently of other subsystems without knowing the type of the objects in the other subsystems. They can be connected to other objects and can transmit messages to them. For this purpose, a first object is generated for cooperating with an abstract object. The abstract object has a defined interface which is called up using the first object and which inherits the abstract object from a second object, the generated second object being unknown to the first, and the second object being intended for cooperation with the first object. The first object which cooperates with the second object considers the second object as an object of the abstract type. However, in this method known from EP-A-0 817 422, there is no use of programming technology which takes into consideration the allomorphy in accordance with the section 5.2.3 of the standard X.720. 
     An object of the present invention, therefore, is to provide a simple method for operating a telecommunications network in which allomorphy is taken into consideration. 
     SUMMARY OF THE INVENTION 
     In the method according to the present invention, in each case a class identifier in which the class to which the maintenance message relates is specified is determined from the maintenance messages during the processing of an interface program which is used for a number of application programs. The class identifier in the maintenance message specifies the class, known in the service computer, of an application object to be processed. As a result of the development, the class known in the service computer sometimes deviates from the actual class of the application object. When the interface program is processed, an alternative identifier is determined by reference to the class identifier, the alternative identifier specifying an alternative class to which the application object in the network element is assigned. The alternative identifier is incorporated into an amended maintenance message. When the amended maintenance message is processed by an application program, the application object is then processed as belonging to the alternative class. This is possible because the application object is allomorphous with respect to the class which is known in the service computer and which is required for the application object in the unamended maintenance message by the service computer. 
     The interface program performs the assignment of the alternative identifiers to the class identifiers centrally for a number of application programs. In the method according to the present invention, this step does not have to be programmed in each application program, but rather only once in the interface program. Given several hundred application programs per control computer, this reduces the complexity of programming, maintenance and documentation considerably. The application programs are kept free of additional steps which are necessary when taking allomorphy into consideration because these steps are carried out centrally in the interface program which is situated upstream. 
     Some of the additional steps are also carried out in databases which are situated downstream and which are utilized by the application programs. 
     The execution of the assignment of alternative identifiers and auxiliary identifiers in a central interface program is possible because allomorphy is defined at the class level in the method according to the present invention. Such a definition is not mentioned in the standard X.720, but is nevertheless compatible with the standard. Allomorphy at the class level refers to means that all the objects of the alternative class being carried out as if they were objects of the original class. A definition of allomorphy which is referred to all the objects of the alternative class then does not result in any disadvantages if predefined programming rules are complied with. Examples of such programming rules are explained below in relation to the exemplary embodiments. 
     The method according to the present invention makes it possible to comply easily with the stipulations of the standard X.720. The application programs in the control computer can be developed with a small amount of additional expenditure, in which case it is always ensured that no errors occur when the control network is operated even when programs remain unchanged in the service computer. 
     In one embodiment, a table with which the alternative identifiers are assigned to the class identifier is used in the interface program. The table is stored in the memory of the control computer. An entry in the table is read in that a memory cell which is assigned to the class identifier and contains the alternative identifier belonging to the class identifier is read. To determine the alternative identifier, all that is therefore required is a single read access to the memory. If the alternative identifiers change as a result of developments of the application programs, all that is necessary is to reprogram the memory contents. As such, the contents of the table can be easily replaced or expanded. 
     If, in another embodiment, after the amended maintenance message has been processed, the application program generates a confirmation message in which the class specified during the generation of the application object to be processed is specified as a class identifier, the confirmation message subsequently can be processed by the interface program. For example, when the interface program is processed, it is possible to determine by reference to the class identifier which data are to be removed from the confirmation message. To do this, the table used in the interface program is expanded to such an extent that entries to the permitted data are also associated with each class identifier. The interface program then generates from the confirmation message a new confirmation message which contains only such data of an application object of the class to which the confirmation message refers. 
     The class specified when the application object to be processed is generated is stored in one embodiment as an origin class in the data of the application object to be processed. When the application program is processed, the origin class is then used as a class identifier. This procedure makes the origin class available easily. 
     If, in another embodiment, the confirmation message also contains an auxiliary identifier in which at least one class is designated which is known in the service computer and/or in at least one other service computer as the class to which the application object to be processed belongs, the program in the service computer can determine later, by reference to the auxiliary identifier, how the received confirmation message is to be processed. This is significant, in particular, if the class specified in the class identifier of the confirmation message received by the service computer is not yet known in the service computer. The service computer then determines the class to which the confirmation message refers by reference to the class or classes specified in the auxiliary identifier. The auxiliary identifier contains, in other words, the classes with respect to which the application object is allomorphous. If the confirmation message contains not only the class identifier but also an origin identifier in which the origin class is specified, the requirements of the protocol for the exchange of messages in the control computer and also for the protocol for the exchange of messages between the service computer and control computer can be fulfilled. 
     In another embodiment, at least one class which is known in the service computer and/or in at least one other service computer for the application object is stored as an allomorph class in the data of the application object. When the application program is processed, the allomorph class is then used as an auxiliary identifier. This measure results in an easy-to-manage data structure in which the application objects administer their allomorph classes themselves. It is not necessary to take any additional measures with respect to the allomorph class in the interface program or in the application program. 
     In another embodiment, the interface program is also responsible for other interface functions. For example, for the control of events for defining the processing sequence of the maintenance messages or for protocol adaptations of these messages, referred to in English as “basic encoding”. As a result of this measure, on the control computer there is just a single interface program which is programmed and maintained in a standardized fashion. 
     Additional features and advantages of the present invention are described in, and will be apparent from, the following detailed description of the invention and the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  shows part of a control network for controlling a telecommunications network. 
         FIG. 2  shows the development of an original class A into an expanded class A′, whose objects can be controlled as objects of the old class A during the operation of the control network. 
         FIG. 3  shows the processing of messages in the control computer of a switching unit after the development, an object being controlled which has been generated before the development. 
         FIG. 4  shows the processing of messages in the control computer after the development, an object being controlled which has been generated after the development. 
         FIG. 5  shows the association of the names of classes A and A 1  and an access to objects of the two classes via a filter function. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows part of a control network  10  for controlling a telecommunications network  12 . The telecommunications network  12  contains a multiplicity of switching offices, of which the switching offices  14  and  16  are illustrated in  FIG. 1 . The telecommunications network  12  also includes connecting lines between the switching offices, of which a connecting line  18  between the switching office  14  and the switching office  16  is illustrated in  FIG. 1 . The telecommunications network  12  connects the subscribers of the telecommunications network  12 ; for example, a subscriber Tln 1  connected to the switching office  14  and a subscriber Tln 2  connected to the switching office  16 . 
     The control network  10  contains dedicated transmission links  20  and  22  which lead to a service computer  24 . The transmission link  20  transmits maintenance messages from the service computer  24  to the switching office  14  in order, for example, to change subscriber data of the subscriber Tln 1  in the switching office  14 . The switching office  14  itself transmits confirmation messages to the service computer  24  in order to signal satisfactory processing of the received maintenance message. The transmission link  22  serves for bidirectional transmission of data between the service computer  24  and switching office  16 . 
     The maintenance messages are processed in the switching office  14  by a control computer  34  and in the switching office  16  by a control computer  36 . The data structures to which the maintenance messages refer belong to the same class A in the service computer  24  and in the switching office  14 . The switching office  16  on the other hand contains data structures of a class A′, which have been developed in comparison with the class A required in the service computer  24 . Error-free operation of the control network  10  is ensured with respect to the switching office  16  by virtue of the fact that allomorphy has been taken into consideration in the development of the class A into class A′. What allomorphy refers to in this context is explained below with reference to  FIG. 2 . 
     In the exemplary embodiment illustrated in  FIG. 1 , the class A which defines, for example, the data structure of the subscriber data, for example the call number and the useable services of the telecommunications network  12 , is used in the switching office  14 . The subscriber data of the subscriber Tln 1  is stored in an object a 1  in accordance with the data structure predefined by the class A in a memory  38  of the control computer  34 . The class A is also known in the service computer  24 , indicated by the letter A in a memory  40  of the service computer  24 . 
     In the switching office  16 , the class A was developed into the class A′. An object a 2  contains, for example, the subscriber data of the subscriber Tln 2 . The object a 2  was firstly stored in the memory  42  before the class A was developed into the class A′. However, in the development, the original object a 2  was converted, specifically into an expanded object a 2  of the class A′ by supplementing a data field. An object a 3  in the memory  42  belongs to the class A′ and contains the subscriber data of a subscriber Tln 3  whose connection was not set up in the switching office  16  until after the development. Although the programs in the service computer  24  only support objects of the class A, the objects a 2  and a 3  belonging to the class A′ can be interrogated, amended or newly set up as objects of the class A from the service computer  24 . The expansions of the class A′, in comparison to the class A cannot, however, be processed by the service computer  24  until the programs in the service computer  24  have been amended at a later time in such a way that the class A′ is also known in the service computer  24 . 
       FIG. 2  shows the classes A and A′ and the original object a 2  and the object a 3 . Below, the meaning of the designation “allomorphous with respect to” is explained in conjunction with  FIG. 2 . The class A′ differs from the class A only by having an additional data field  50 . The data structure of the class A has therefore been expanded by the data field  50  in order to be able to take into consideration a further property of the subscribers Tln 2 , Tln 3  during the operation of the switching office  16 ; for example, whether the subscriber Tln 2 , Tln 3  is connected to the switching office  16  via an optical waveguide or via a copper conductor. For this reason, the class A′ is also designated below as an expanded class A′. A data field  50 ′ in the object a 3  contains, as data item, a value which indicates that the subscriber Tln 3  is connected to the switching office  16  via an optical waveguide. The object a 3  is generally designated as an expanded object a 3 . 
     The class which is specified when an object is generated is designated as an original class of this object. The object a 2  had, as original class, the class A indicated by an arrow  52 . On the other hand, the expanded object a 3  has, as original class, the expanded class A′ indicated by an arrow  54 . 
     A first possible way of defining the data structure of the class A includes generating the class A′ from the class A via what is referred to as inheritance which is defined in object-oriented programming languages. Such programming languages are, for example, the languages C++ and CHILL. When inheritance occurs, the programmer specifies that the expanded class A′ is to take over all the data structures and what are referred to as methods for processing the data structures from the class A. It is also specified that the class A′ additionally contains the data field  50 . Another possible way of defining the class A′ is to redefine this class. In this case, the class A′ is defined in the way in which it was already defined in class A. However, in addition, the data field  50  is also defined. The relationship between the corresponding parts of class A and of the expanded class A′ is illustrated in  FIG. 2  via dashed lines  56 . 
     An imaginary object a 3 * contains, from the object a 3 , all the data fields and all the methods for processing the data fields which also would have been generated when the subscriber Tln 3  is set up before the development, when the class A existed, but the class A′ did not yet exist. In the object a 3 *, there is for this reason no data field corresponding to the data field  50  or  50 ′. This fact is indicated by dashed lines  58 . The object a 3 * is a visual aid for delimiting the terms “compatible with” and “allomorphous with respect to”. An arrow  60  indicates that the object a 3 * is compatible with the class A because it has precisely the data structures which are predefined in the class A. The expanded object a 3  is on the other hand allomorphous with respect to the class A, cf. arrow  62 . The object a 3  has the allomorphous class A. 
     Allomorphy is the ability of the objects in class A′ to be controlled as if they were objects of their allomorphous class A if this ability arises as a result of measures on the part of the application program. In an incremental expansion it is possible for there to be more than one allomorphous class; for example, the allomorphous class of the last expansion and the allomorphous class of the penultimate expansion. 
     An expanded object has only one allomorphous class if the expanded object is compatible in accordance with standard X.720 section 5.2.2 without the expansions to form the allomorphous class. In particular, the expanded object accordingly has all the attributes, attribute groups, control functions and confirmation methods which are also defined in the allomorphous class. Making allowance for allomorphy in the expansion of the class A ensures that the control network  10  also operates without errors after the expansion. 
       FIG. 3  shows the processing of messages in the control computer  16  after the development of the class A into the class A′, the object a 2  which has been configured before the development as belonging to the class A being controlled. During the development of the class A into the class A′, allomorphy was taken into account so that objects of the class A′ are allomorphous with respect to the class A. In addition, in the development all the objects of the class A were converted into objects of the class A′ through supplementing data fields and methods. 
     The control computer  16  contains an interface program  100  which processes maintenance messages coming from the service computer  24 , for example a maintenance message WN 1 , and which transmits confirmation messages, for example a confirmation message BN 1 ′, to the service computer  24 . The interface program  100  is the interface between the service computer  24  and a number of application programs in the control computer  16 , of which two application programs  102  and  104  are shown in  FIG. 3 . The application program  102  serves to administer the data associated with the subscribers Tln 2 , Tln 3  connected to the switching office  16 . The application program  104  is used for traffic measurement. 
     The maintenance message WN 1  coming from the service computer is passed on, as amended maintenance message WN 1 ′, to the application program  102  when the interface program  100  is processed. On the other hand, maintenance messages which are intended for the application program  104  are passed on to the application program  104 , cf. arrow  106 , when the interface program  100  is processed. 
     After the processing of the maintenance message WN 1 ′ in the application program  102 , the application program  102  generates a confirmation message BN 1  for the interface  100 . If the application program  104  has processed a maintenance message, it also transmits a confirmation message to the interface program  100 , cf. arrow  108 . 
     During the processing of the maintenance message WN 1 ′, the application program  102  cooperates with a database program  110  which is also present in the control computer  36  and is used to store, change, delete or read subscriber data in the memory  42 . The application program  102  transmits requests in the form of messages to the database program  110 ; for example, the message N 1 . After the request in the message N 1  has been executed, the database program  110  transmits a result message EN 1  back to the application program  102 . The application program  104  cooperates with its own database program  112  by transmitting requests to the database program  112 , cf. arrow  114 , and by receiving and further processing result messages from the database program  112 , cf arrow  116 . 
     The database program  110  uses the same access method for the objects of the original class A and the objects of the developed class A′. This is possible because combination classes are used in which the data structures and methods of the original class and of the expanded class are combined. A combination class KA is the combination of the class A and of the class A′. All the objects in the memory  42  which have the allomorphous class A as original class are expanded during the development by the additional data fields of the expanded class A. The additional data fields are filled with predefined values. 
     The maintenance message WN 1  contains a class identifier moC which specifies the class A as the class to which the maintenance message WN 1  refers. An object identifier moI specifies the object a 2  to which the maintenance message WN 1  refers. The maintenance message WN 1  is transmitted by the service computer  24  in order to find out the subscriber data of the subscriber Tln 2 . All that is known in the service computer  24  is that this subscriber data is contained in the object a 2  which is stored in the control computer  36 . The maintenance message WN 1  contains further data fields which are not illustrated. The read operation to be carried out, for example, is defined in one of these data fields. 
     When the maintenance message WN 1  is processed in the interface program  100 , the class A specified in the class identifier moC is determined. When the interface program  100  is processed, the class A′ is determined as an alternative class via a table T by reference to the class A which is determined in this way, and the class A′ is entered into the class identifier moC of the maintenance message WN 1 . The table T is stored in a memory  122  of the control computer  36 . 
     The maintenance message WN 1 ′ relates, with the class identifier moC=A′, to the expanded class A′. The value of the object identifier moI=a 2  remains unchanged in the maintenance message WN 1 ′. An identifier allo in the maintenance message WN 1 ′ specifies all the classes which are allomorphous with respect to the class A′, i.e. in the exemplary embodiment the class A. The interface program  100  also obtains these classes from the table T. The other data of the maintenance message WN 1  are transferred into the maintenance message WN 1 ′. When the maintenance message WN 1 ′ belonging to the maintenance message WN 1  is generated, the interface program  100  also carries out protocol adaptation of a transmission protocol on the transmission link  22  into a message protocol which is used within the control computer  36 . 
     The message N 1  which is generated by the application program  102  during the processing of the maintenance message WN 1 ′ contains an instruction B 1  which specifies that data is to be read. As a parameter of the instruction B 1 , the message N 1  contains the class A′ to which the data to be read belongs, as well as the object a 2  whose data is to be read. The application program  102  processes exclusively messages which refer to objects of the class A′. No further measures are taken in the application program  102  with respect to the class A. 
     The database program  110  accesses the memory  42  during the processing of the message N 1  in order to read the data of the subscriber Tln 2  which is stored in the object a 2 . The object a 2  also contains an origin identifier oC in which the class which has been specified when the object a 2  was generated is specified. The database program  110  reads the data requested with the instruction B 1  in the object a 2  and enters this data into the result message EN 1 . In addition, in the result message EN 1  there is a note, via a response identifier AB 1 , that the result message EN 1  contains the result which has been generated when the instruction BI was processed. 
     Furthermore, in the result message EN 1  the class A′ is specified as the class which has been affected by the result message EN 1 . The origin identifier oC=A is also transferred from the database program  110  in the result message EN 1  to the application program  102 . 
     When the application program  102  is processed it is a prerequisite that all the messages to be processed refer to the class A′ and not to the class A. The value of the origin identifier oC=A is transferred as a value of the class identifier moC in the confirmation message BN 1  by the application program  102 . For this value assignment it is not necessary for the application program  102  to be able to process objects of the class A. In addition, the confirmation message BN 1  contains the origin identifier oC=A and the interrogated subscriber data of the subscriber Tln 2 . The interface program  100  does not need to remember the class identifier of the maintenance message WN 1  by virtue of this procedure. 
     The confirmation message BN 1  is processed by the interface program  100  and transmitted, as confirmation message BN 1 ′, to the service computer  24  on the transmission link  22  in accordance with the transmission protocol. By reference to the table T, the interface program  100  determines which data fields in the message BN 1  are not contained in objects of the class A. These data fields are not transferred into the confirmation message BN 1 ′. 
     The service computer  24  receives the confirmation message BN 1 ′ and can process it as a message which refers to an object of the class A. Objects of the class A′ in the control computer  36  are controlled from the service computer  24  as if they were objects of the class A. The development in the control computer  36  does not, therefore, restrict the operating features of the service computer  24 . 
       FIG. 4  shows the processing of messages in the control computer  16  after the development of the class A into the class A′, the object a 3  which is not generated until after the development being controlled. 
     Via inputs by an operator into the service computer  24 , a maintenance message WN 2  is generated in the service computer  24 , the maintenance message WN 2  having the function of generating in the control computer  16  the object a 3  for the subscriber data of the subscriber Tln 3 . For this reason, the maintenance message WN 2  contains a coding for the instruction “Generate” in an instruction field. The class identifier moC in the maintenance message WN 2  identifies the class A as the class to which the maintenance message WN 2  refers. The object identifier mol of the maintenance message WN 2  identifies the object a 3  which is to be generated via the maintenance message WN 2 . The maintenance message WN 2  also contains further data which is not illustrated. 
     The interface program  100  processes the maintenance message WN 2  in the same way as explained above for the maintenance message WN 1 . When the maintenance message WN 2  is processed, the table T stored in the memory  122  is again used to determine the alternative class A′ for the class A specified in the class identifier moC of the maintenance message WN 2  and to use it as the class identifier moC of the maintenance message WN 2 ′. The object identifier moI=a 3  has the same value in the maintenance message WN 2 ′ as in the maintenance message WN 2 . The remaining data is also transferred from the maintenance message WN 2  into the maintenance message WN 2 ′ when the interface program  100  is executed. In addition, in the identifier allo of the maintenance message WN 2 ′, it is noted that the class A is the class with respect to which the class A′ is allomorphous. The maintenance message WN 2 ′ generated in this way is transmitted from the interface program  100  to the application program  102  in accordance with the protocol in the control computer  36 . 
     When the maintenance message WN 2 ′ is processed, the application program  102  transmits a message N 2  to the database program  110  in order to allow the object a 3  to be created in the memory  42 . The message N 2  contains, in encrypted form, the instruction “Generate”, the expanded class A′ and the name of the object a 3  to be created. 
     When the message N 2  is processed, the object a 3  is generated in the memory  42  via the database program  110  by assigning to this object specific memory cells which are filled with initial values. In the origin identifier oC of the object a 3  there is a note of the class A′ because this class was specified when the object a 3 ′ was generated. An identifier allo in the object a 3  refers to the class A because the object a 3  is allomorphous with respect to the class A. 
     The database program  110  generates a result message EN 2  in order to confirm the generation of the object a 3 . The result message EN 2  contains a response identifier AB 2  which specifies that the result message EN 2  was produced when an instruction “Generate” was produced. In addition, the result message EN 2  contains an identifier which refers to the class A′, the origin identifier oC=A′, the identifier allo=A and further data (not illustrated) of the object a 3 . 
     The result message EN 2  is processed by the application program  102 , a confirmation message BN 2  being generated. The value of the origin identifier oC=A′ is used as a value of the class identifier moC in the confirmation message BN 2 . The other data items in the result message EN 2  are transferred into the confirmation message BN 2 . 
     When the interface program  100  is processed, after the reception of the confirmation message BN 2 , a confirmation message BN 2 ′ is generated in accordance with the transmission protocol used on the transmission link  22 . The confirmation message BN 2 ′ contains all the data of the confirmation message BN 2  because the interface program  100  determines, by reference to the table T, that it is not necessary to remove any data fields if the confirmation message BN 2  has the class A′ as class identifier. 
     During the processing of the confirmation message BN 2 ′ in the service computer  24 , it is determined by reference to the identifier allo that the confirmation message BN 2 ′ relates to data of an object of the class A or that the confirmation message BN 2 ′ can be treated as if it contained data of an object of the class A. Although the program in the service computer  24  has not been changed after development in the control computer  36 , objects of the class A′ in the control computer  36  can be controlled from the control computer  24  as if they were objects of the class A. As long as only the class A is known in the service computer A, it is also the case that only the data items contained in objects of the class A are processed in the confirmation message BN 2 ′. 
     Via the method explained with reference to  FIGS. 3 and 4 , it is also possible to support classes which are allomorphous with respect to a number of classes. If, for example, the class A′ is developed into a class A″, objects can be allomorphous with respect to the classes A′ and A. The control computer  36  then can be executed by service computers  24  during whose programming at least one of the classes A, A′ or A″ was known. It is possible to dispense with the class A as soon as all the service computers know at least the class A′. 
     The method explained with reference to  FIGS. 3 and 4  is applied in maintenance messages for generating objects, and in maintenance messages for reading objects. In addition, this method can be used to change data in objects and delete objects. For these methods to operate without errors, the service computer  24  must be capable:
         of assigning the confirmation messages BN to the associated maintenance messages WN,   of reading and evaluating the identifier alto in the confirmation messages BN,   of skipping over unknown name associations (cf. explanations relating to  FIG. 5 ) and unknown identifier values and parameters,   of storing the origin class of an object if there is a database in the service computer,   of skipping over unknown optional values, and   of skipping over unknown values of the “enumerated” data type.       

     In other words, the service computer  24  must be programmed in such a way that objects can be transferred from it into a control computer with a greater degree of knowledge. 
     The interface program  100  has the following features:
         When a class is expanded it is necessary to incorporate the expanded class into the table T, such that for each expanded class it is necessary to store the classes with respect to which the expanded class is allomorphous.   The name associations which have been made by the expanded class must be stored in the table T.   The interface program  100  is to remove from the confirmation messages BN coming from the application program  102  the data which does not belong to the compatible class if the confirmation message BN transmitted to the service computer  24  does not relate to the non-expanded class.   The interface program  100  must be able to process filter instructions. This is explained in more detail below with reference to  FIG. 5 .       

     The application program  102  fulfills the following requirements:
         As soon as the system moves over to the expanded class, only objects of the new class are then generated, irrespective of the knowledge of the service computer.   The new classes are either expanded classes or classes which have nothing to do with the previous classes.       

     The database program  110  is configured in such a way that, after a development, the entire data stock relating to the origin class is converted into a data stock of the expanded class. 
     The creation of the table T and the conversion of the data stock in the database of the database program  110  are supported by service programs. These service programs evaluate description languages which are used to specify the expansion of classes. 
     Conditions which have to be complied with when taking into consideration allomorphy are dealt with below. These conditions apply on the level of the classes although, according to standard X.720, allomorphy is firstly a property of an object. In the standard X.720, the following conditions are mentioned:
         conditions for the expanded class in section 5.2.2.1,   conditions for what are referred to as program packages in the sections 5.2.2.1 and 5.2.2.2,   conditions for identifier values in the sections 5.2.2.3 and 5.3.4.1,   conditions for what are referred to as identifier groups in section 5.2.2.4,   conditions for actions, confirmations and parameters in section 5.2.2.54,   conditions for the behavior of the objects in section 5.2.2.6, and   conditions for the name association in section 5.3.4.1.       

       FIG. 5  shows, in a part a, a section of what is referred to as a binary tree which defines the name association of objects of the class A and A′. Name association is the assignment of the object to what is referred to as a superordinate object, the assignment being used for the definition of a uniquely defined name for an object. Identical object names for different objects can be used if the objects each belong to another superordinate object. A name which is uniquely defined in the control computer  16  is then produced from the name of the superordinate object and the name of the objects which are subordinated in this way. The superordinate object is to be specified when an object is generated. The subordinate object is considered as being contained in the superordinate object, referred to in English as “containment”. 
     An object b 1  of the class B is the superordinate object for the objects a 2  and a 3 , which both belong to the class A′ after the development, but have different original classes oC=A and oC=A′. The name associations are noted in the table T which is used by the interface program  100 . 
     For the portion of the name tree shown in part A of  FIG. 5  there is a note in table T that objects of the class B contain subordinate objects of the original class A and of the class A′. At each development, the name associations in the table T are also adapted to the name tree which is also decisive after the development. 
     In part b of  FIG. 5 , an access to objects of both classes A and A′ is illustrated after the service computer  24  also knows both classes A and A′. A maintenance message WN 3  contains a filter instruction F 1 =((oC=A) OR (oC=A′)) in which it is defined that subordinate objects of the class A or A′ are to be registered. The class identifier moC=B of the maintenance message WN 3  specifies that the maintenance message WN 3  also refers to the class B. The object identifier moI=b 1  of the maintenance message WN 3  specifies that the object b 1  is to be processed; i.e., is the superordinate object. 
     When the interface program  100  is executed in the switching office  16 , the filter instruction F 1  is transmitted unchanged to the application program  102 . As such in particular, that operations which refer to the original class A do not have to be replaced in the filter instruction F  1  by operations which refer to the expanded class A′. This measure ensures that the service computer  24  can distinguish between objects of the original class A and of the original class A′. 
     The application program  102  causes the data of the objects a 2  and a 3  whose original class is the class A and A′, respectively, to be read from the memory  42  via database program  110 . Two confirmation messages BN 3  and BN 4  (not illustrated) are transmitted to the interface program  100 . A new confirmation message BN 3 ′, which contains the class identifier moC=A, the object identifier moI=a 2 , the origin identifier oC=A and the auxiliary identifier allo={ } is generated from the confirmation message BN 3  in the interface program  100 . A confirmation message BN 4 ′, which contains the class identifier moC=A′, the object identifier moI=a 3 , the origin identifier oC=A′ and the auxiliary identifier allo={A} is generated from the confirmation message BN 4  in the interface program  100 . 
     The CCITT standard X.734 “Information Technology—Open Systems Interconnection—Systems Management: Event Report Management Function” from 1993 explains event control in the control network  10 , cf.  FIG. 1 . What are referred to as discriminators are used which pass on events to the service computer  24  within the switching office  16  only under certain conditions. After the development of the class A into the class A′, it is sufficient to convert the discriminators which relate to the class A into discriminators which relate to the class A′. If new discriminators are generated after the development, the class A is replaced by the class A′ if the class A is specified as a selection criterion for the passing on of the messages. 
     Although the present invention has been described with reference to specific embodiments, those of skill in the art will recognize that changes may be made thereto without departing from the spirit and scope of the invention as set forth in the hereafter appended claims.