fig1 shows — purely by way of an example — a production machine 1 . the production machine 1 features different elements 2 to 14 . the following are shown as examples in fig1 : a chassis unit 2 , a tool carriage 3 , which is able to be moved by means of a carriage spindle 4 and a carriage drive 5 , a first and a second workpiece holder 6 , 7 , each of which has a chuck 8 , 9 and which can be moved by means of a holder drive 10 and a holder spindle 11 in relation to one another , a workpiece drive 12 , by means of which a workpiece 12 ′ can be rotated around an axis of rotation 12 ″, and a tool magazine 13 , containing a number of tools 14 . elements 2 to 14 are mechanically connected to one another via interfaces . for example the carriage drive 5 is connected via schematically indicated threaded bolts 15 to the chassis unit 2 . the associated bolt guides of the chassis unit 2 and of the carriage drive 5 thus represent a part of the mechanical interface between the chassis unit 2 and the carriage drive 5 . furthermore the carriage drive 5 is connected via corresponding connection elements to the drive spindle 4 . this connection too represents a mechanical interface , here between the carriage spindle 4 and the carriage drive 5 . similar embodiments apply for the other of the elements 2 to 14 . thus for example the workpiece carriage 3 must be adapted to the diameter and the thread pitch of the carriage spindle 4 . electrical interfaces are also provided , especially terminals for energy , signal and communication lines . these interfaces too must be suitably connected to one another . for example an electrical interface can have screw terminals for connecting individual conductors or can have a multipin prefabricated plug - in connector . data systems interfaces must also be taken into account . data transfer rate , protocol , signal type etc . are considered for example . the production machine 1 is controlled in accordance with fig2 by a control device 16 . to this end the control device 16 has a memory 17 which holds a control program 18 as one of its programs . the control program 18 is read out and executed by a processor 19 of the control device 16 . according to the control program 18 the processor 19 controls the production machine 1 via a machine interface 20 . a present configuration 21 and descriptions 21 ′, 21 ″ can be stored in the memory 17 . the present configuration 21 and the descriptions 21 ′, 21 ″ can be output via an operator interface 22 to an operator 23 of the production machine 1 , in some cases it is also able to be retrieved and changed . for this purpose the operator interface 22 preferably includes a visual display unit and an input device ( for example keyboard and / or cursor control ). in accordance with fig2 the descriptions 21 ′ are stored in a reservoir area 24 of the memory 17 , the descriptions 21 ″ in a configuration area 25 of the memory 17 . the descriptions 21 ′, 21 ″ stored in the control device 16 are explained in greater detail below with reference to fig3 . the descriptions 21 ′ are element descriptions 21 ′. in accordance with fig3 they each describe a possible element 26 of the production machine 1 . the element descriptions 21 ′— specifically for the respective possible element 26 — have the following contents : a list of the available interfaces of the respective possible element 26 and a description of these interfaces . on the one hand the descriptions contain a plain text part which can be output via the operator interface 22 to the operator 23 , on the other hand a part prepared for data processing which is used internally by the control device 16 in order to determine which other possible elements 26 are able to be connected with which of their interfaces to the respective interface of this possible element 26 . installation information about whether the respective possible element 26 is to be connected via its interface to other possible elements 26 . dismantling information about how the respective possible element 26 is able to be disconnected from other possible elements . commissioning information about how the respective possible element 26 is to be put into operation . a list of possible parameters and the maximum or minimum permitted limit values for these parameters . the installation , dismantling and commissioning information is held in plain text , for example in ascii code , and is able to be output via the operator interface 22 to the operator 23 . the descriptions 21 ′ stored in the reservoir area 24 are able to be changed by the operator 23 . however it is also possible for them not to be able to be changed by the operator 23 . at least one required configuration description 21 ″ is stored in the configuration area 25 . if necessary a number of required configuration descriptions 21 ″ can also be held in the configuration area 25 . if more than one required configuration description 21 ″ is held in the configuration area 25 there should also be a flag to indicate which of the required configuration descriptions 21 ″ is valid (= activated ) at the time . the required configuration descriptions 21 ″ are able to be requested via the operator interface 22 by the operator 23 . if the operator 23 enters a request of this type , the requested required configuration description 21 ″ is output by the control device 16 via the operator interface 22 to the operator 23 . it can then be changed by the operator 23 . in accordance with fig3 each required configuration description 21 ″ includes for each element 2 to 14 that the production machine 1 has in accordance with the respective required configuration description 21 ″, an instantiation of one of the element descriptions 21 ′ which are stored in the reservoir area 24 . the instantiations are parameterized . the possible parameters of the respective elements 2 to 14 are thus assigned actual values . furthermore the respective instantiations are obviously assigned the information about which of the elements 2 to 14 are connected to the respective instantiated element 2 to 14 . the required configuration description 21 ″ thus includes which of elements 2 to 14 the production machine 1 features and via which interfaces the elements 2 to 14 are connected to one another . the present configuration 21 can also be stored in the configuration area 25 . it can be requested via the operator interface 22 by the operator 23 . in the event of a request via the operator interface 22 it is output to the operator 23 . the present configuration 21 contains a configuration part 21 a and an element part 21 b . both the configuration part 21 a and also the element part 21 b are requested by the operator 23 . the form of the configuration part corresponds to a required configuration description 21 ″. it can be accepted by the operator 23 as the required configuration description 21 ″. however it is not possible for the operator 23 to change the configuration part 21 a . he can only make changes if he has transferred the configuration part 21 a as a required configuration description 21 ″. the element part 21 b contains dynamic data of elements 2 to 14 of the production machine 1 . for example the element part 21 b contains the run times , the time of the last maintenance or inspection , the wear state etc . of elements 2 to 14 of the production machine 1 . the element part 21 b is able — at least partly — to be changed by the operator 23 . the interaction of the control device 16 with the operator 23 is now described in conjunction with fig4 , where it relates to the descriptions 21 ′, 21 ″ stored in the control device 16 . in accordance with fig4 the control device 16 in a step s 1 , accepts an input from the operator 23 entered via the operator interface 23 . in a step s 2 the control device 16 tests whether the operator input is a choice of a required configuration description 21 ″. if it is , the control device 16 determines in a step s 3 which required configuration description 21 ″ the operator 23 has chosen . in addition the control device 16 accepts the chosen required configuration description 21 ″ into a buffer 27 and outputs it via the operator interface 22 to the operator 23 . if the input of step s 1 is not a choice of a required configuration description 21 ″, the control device , 16 tests in a step s 4 , whether the input of the step s 1 is a change specification for the chosen required configuration description 21 ″. if it is , the control device 16 , in a step s , changes the chosen required configuration description 21 ″ in accordance with the change specification . the changes are however only made in relation to the required configuration description 21 ″ stored in the buffer 27 . the required configuration description 21 ″ stored in the configuration area 25 is not changed . step s 5 will be examined in more detail below in conjunction with fig5 . if the input of step s 1 is also not a change specification , the control device 16 tests , in a step s 6 , whether the input is a request to output information about installation , dismantling or commissioning of an element 2 to 14 . if this is the case , the control device 16 outputs the requested information to the operator 23 in a step s 7 via operator interface 22 . if the input of the step s 1 is also not an information request , the control device 16 tests , in a step s 8 , whether previous inputs are to be stored . if they are , the control device 16 also tests , in a step s 9 , whether the required configuration description 21 ″ stored in the buffer 27 is to replace the corresponding original required configuration description which is stored in the configuration area 25 . if it is , the control device 16 , in a step s 10 , stores the required configuration description 21 ″ buffered in the buffer 27 instead of the original required configuration description 21 ″ in the configuration area 25 . else the control device 16 executes a step s 11 , in which its stores the required configuration description 21 ″ buffered in the buffer 27 in the configuration area 25 in addition to the required configuration description 21 ″ already stored there . the control device 16 is thus able to store the required configuration description 21 ″ changed by the operator 23 in the control device 16 as an alternative or in addition to the original required configuration description 21 ″. the control device 16 also then executes a step s 12 . in step s 112 the control device 16 clears the buffer 27 , provided the required configuration description 21 ″ was previously stored there . step s 12 is also executed if the information is not to be stored in the configuration area 25 . in accordance with fig5 , step s 5 of fig4 for example can be implemented as follows : in a step s 21 the control device 16 tests whether the change specification of the user 23 is a selection entry for one of the elements 2 to 14 . if it is , the control device 16 , in a step s 22 outputs the description of the respective element 2 to 14 or at least a part of this description 23 . furthermore the control device 16 flags this element 2 to 14 internally as chosen . if the change specification is not a choice of an element 2 to 14 , the control device 16 tests , in a step 23 , whether the input was a specification to change a parameter . if it is , the control device 16 , in a step s 24 outputs the parameters of the chosen element 2 to 14 via the operator interface 23 to the operator 22 . in a step s 25 it accepts the appropriate parameter specifications . if the change specification of step s 1 was neither the choice of an element 2 to 14 nor the specification of a parameter , the control device 16 tests , in a step s 26 , whether the operator 23 has chosen one of the interfaces of the previously chosen element 2 to 14 . if he has , the control device 16 determines on the basis of the description of the chosen interface and the descriptions of the interfaces of the possible elements 26 , which possible elements 26 are able to be connected to the chosen interface . when determining the possible elements 26 able to be connected to the chosen interface , the control device 16 preferably takes account of which elements 2 to 14 are already connected to the other interfaces of the specific element 2 to 14 . in a step s 28 the control device 16 outputs the descriptions 21 ′ of the possible elements 26 ( or a part of the descriptions ) determined in step s 27 via the operator interface 22 to the operator 23 . in a step s 29 the control device 16 finally accepts a corresponding choice of one of the possible elements 26 from the operator 23 . in the operation of the production machine 1 the control device 16 preferably initially determines in accordance with fig6 in a step s 31 the actual configuration of the production machine , provided this is possible for the control device 16 . it then tests in a step s 32 , whether a present configuration 21 is already stored in the configuration area 25 . if no present configuration 21 is yet stored in the configuration area 25 , the control device 16 , in a step s 33 , stores the actual configuration just determined as the present configuration 21 . in this case both the configuration part 21 a and also the element part 21 b are stored . if a present configuration 21 is already stored in the configuration area 25 , the stored present configuration 21 is updated in a step s 34 with the information of the actual configuration . in the updating of the present configuration 21 the configuration part 21 a will be overwritten and data of the element part 21 b retained , where this is sensible and possible . in a step s 35 , the control device 16 tests whether the actual configuration of the production machine 1 determined in step s 31 matches the configuration of the production machine 1 in accordance with the required configuration description 21 ″ ( or , for a number of required configuration descriptions 21 ″, matches the configuration in accordance with the activated required configuration description 21 ″). if the actual configuration ( i . e . the configuration part 21 a ) matches the required configuration description 21 ″, the control device 16 branches to a step s 36 . if on the other hand deviations are produced , the control device 16 , in a step s 37 , outputs a warning message to the operator 23 via the operator interface 22 and waits for an input from the operator 23 . in a step s 38 , the control device 16 tests whether the operator entry of step s 37 is a command for accepting the configuration part 21 a as the new required configuration description 21 ″. if it is , the control device 16 , in a step s 39 , accepts the configuration part 21 a as the new required configuration description 21 ″, if necessary marks this new required configuration description 21 ″ as activated and moves on to step s 36 . depending on the type of user entry the new required configuration description 21 ″ can displace the previous required configuration description 21 ″ or be stored in addition to the previously stored required configuration description 21 ″ in the configuration area 25 . if the operator entry of step s 37 is not a command for accepting the configuration part 21 a , the control device 16 tests , in a step s 40 , whether the operator entry is a command for continuing the control of the production machine 1 . if it is not , the further processing of the control program 18 is aborted in a step s 41 . if a branch is made to step s 36 , the control device 16 controls the production machine 1 by executing the control program 18 . likewise within the framework of step s 36 the control device 16 monitors the elements 2 to 14 of the production machine 1 for correct functioning . if sensible and possible , the control device 16 within the framework of step s 36 , can also update the dynamic data of the element part 21 b . in a step s 42 the control device 16 tests whether the elements 2 to 14 are functioning correctly . if they are , the control device 16 returns to step s 36 . otherwise the control device 16 determines , in a step s 43 , at which of the elements 2 to 14 the malfunction has occurred . in a step s 44 it outputs via the operator interface 22 a message to the operator 23 , on the basis of which the operator 23 can identify at which of the elements 2 to 14 the malfunction has occurred . the message can especially be a project planning diagram of the production machine 1 — e . g . a diagram similar to that shown in fig1 , in which there is a visual highlight to indicate in which of the elements 2 to 14 the malfunction has occurred . the visual highlight can for example consist of the element 2 to 14 in which the malfunction has occurred being shown flashing and / or in a color different from the remaining elements 2 to 14 . the faulty element 2 to 14 can also be marked for example by means of an arrow 28 ( see fig1 ). a combination of different measures is also possible . the control device 16 thus allows convenient in - situ configuration and reconfiguration of the required configuration description 21 ″, i . e . at the production machine 1 .