What is claimed is: 1. A computer-implemented method, the method comprising: a decision service manager authenticating at a managed system, the managed system hosting a decision service; in case of a successful authentication at the managed system, the decision service manager sending a first status request to the managed system; the decision service manager receiving, in response to the first status request, a first indication of a current status of the managed system; the decision service manager authenticating at a target managed system; in case of a successful authentication at the target managed system, the decision service manager sending a second status request to the target managed system; the decision service manager receiving, in response to the second status request, a second indication of a current status of the target managed system; the decision service manager performing a deployment readiness check, the check comprising comparing the first and the second indication; and in case the deployment readiness check returns as result that a current status of the target managed system allows the target managed system to host the decision service, automatically, by a hardware processor, deploying the decision service to the target managed system. 2. The computer-implemented method of claim 1, further comprising: the decision service manager outputting the second indication to a user of the decision service manager; and the decision service manager receiving the decision service from the user, the decision service being received in a modified form, the modifications of the decision service having been implemented in accordance with the current status of the target managed system. 3. The computer-implemented method of claim 1, wherein the first indication comprises a specification of resources being available at the managed system and comprises a description of each decision service being currently hosted on the managed system, wherein the resources are, in particular, available databases and respective access credentials, database tables, network cards, processors, memory, storage, bus systems, device interfaces and available program libraries. 4. The computer-implemented method of claim 1, wherein deploying the decision service comprises transferring executable code and a service description file to the target managed system, wherein the executable code upon execution by the target managed system provides the deployed decision service and wherein a content of the service description files of all decision services currently being deployed to the target managed system are returned as response in case the target system receives a status request from the decision service manager. 5. The computer-implemented method of claim 1, the authentication of the decision service manager at the managed system being based on: providing a public key to the managed system; providing a private key to the decision service manager, the public and the private key forming an asymmetric cryptographic key pair; and wherein the authentication of the decision service manager at the managed system comprises: the decision service manager signing a secret shared between the decision service manager and the managed system with the private key; the decision service manager sending a signed data value to the managed system; and the target managed system decrypting and evaluating a signature with its public key. 6. The computer-implemented method of claim 1, wherein the deployment readiness check is based upon criteria of the target managed system, including the decision services currently deployed to the target managed system, available resources at the target managed system and on requirements of the service to be deployed, the criteria including at least one of: that the decision service to be deployed does not depend on any resource not available in the target managed system, that the decision service to be deployed does not depend on any other decision service not already been deployed in the target managed system, or that the managed system responded to a request for availability by the decision service manager with an acknowledgement. 7. A computer-implemented method, the method comprising: receiving authentication data from a decision service manager; receiving a status request from the decision service manager; in case of a successful verification of the authentication data, collecting data being indicative of a current status of a managed system; returning the collected data to the decision service manager for enabling the decision service manager for performing a deployment readiness check; receiving a decision service from the decision service manager in case the deployment readiness check returns as a result that a target managed system is operable to host the decision service; and deploying the decision service on the target managed system. 8. The computer-implemented method of claim 7, wherein the method is executed by a business rule service package being installed on the target managed system as a plug-in interfacing with the decision service manager. 9. The computer-implemented method of claim 8, wherein the plug-in further interfaces with one or more client computers, the method comprising: receiving a service call from one of the one or more client computers, the service call requesting a service provided by the deployed decision service; extracting a service time from the service call; accessing a service catalog, the service catalog comprising a mapping of decision services currently deployed in the target managed system and respective availability periods of said decision services; calling, by the business rule service package, the requested decision service if its assigned availability period according to the mapping covers the service time, and returning a result of the called decision service to the client computer; and if the availability period assigned to the requested decision service does not cover the service time, denying execution of the service request. 10. The computer-implemented method of claim 9, further comprising: in case the service call does not comprise a specification of the service time, using a current time as the service time. 11. The computer-implemented method of claim 9, further comprising: switching from test mode into productive mode or vice versa; and executing the service call by calling the requested decision service, whereby any data generated by the called decision service in test mode is managed and stored separately from any data generated by the called decision service in productive mode. 12. The computer-implemented method of claim 7, further comprising: after having received the decision service to be deployed and after having initiated said decision service, locking objects in the target managed system being associated with the deployed decision service, the locking comprising prohibiting any redeployment or un-deployment of other decision services hosted by the targeted managed system from which said deployed and initiated decision service depends. 13. The computer-implemented method of claim 12, further comprising: evaluating a service description file of the decision service received by the target managed system upon deployment of the decision service; extracting an availability period being indicative when the deployed decision service is permitted to execute on the target managed system; and storing the extracted availability period in association with an identifier of the deployed decision service in mapping contained in a service catalog. 14. The computer-implemented method of claim 13, further comprising: evaluating the mapping on a regular basis; in case it is determined that a validity period of any decision service deployed to the target managed system has begun, initiating the respective decision service; and in case it is determined that the validity period of any decision service deployed to the target managed system has ended, stopping execution of the respective decision service. 15. A non-transitory, computer-readable medium storing computer-readable instructions executable by a hardware processor and configured to: receive authentication data from a decision service manager; receive a status request from the decision service manager; in case of a successful verification of the authentication data, collecting data being indicative of a current status of a managed system; return the collected data to the decision service manager for enabling the decision service manager for performing a deployment readiness check; receive a decision service from the decision service manager in case the deployment readiness check returns as a result that a target managed system is operable to host the decision service; and deploy the decision service on the target managed system. 16. The computer-readable medium of claim 15, wherein the computer-readable instructions comprise a business rule service package being installed on the target managed system as a plug-in interfacing with the decision service manager. 17. The computer-readable medium of claim 16, wherein the plug-in further interfaces with one or more client computers and is configured to: receive a service call from one of the one or more client computers, the service call requesting a service provided by the deployed decision service; extract a service time from the service call; access a service catalog, the service catalog comprising a mapping of decision services currently deployed in the target managed system and respective availability periods of said decision services; call, by the business rule service package, the requested decision service if its assigned availability period according to the mapping covers the service time, and return a result of the called decision service to the client computer; and if the availability period assigned to the requested decision service does not cover the service time, deny execution of the service request. 18. A computer system, comprising: a hardware memory; at least one hardware processor interoperably coupled with the hardware memory and configured to: receive authentication data from a decision service manager; receive a status request from the decision service manager; in case of a successful verification of the authentication data, collecting data being indicative of a current status of a managed system; return the collected data to the decision service manager for enabling the decision service manager for performing a deployment readiness check; receive a decision service from the decision service manager in case the deployment readiness check returns as a result that a target managed system is operable to host the decision service; and deploy the decision service on the target managed system. 19. The computer system of claim 18, further configured to execute by a business rule service package being installed on the target managed system as a plug-in interfacing with the decision service manager. 20. The computer system of claim 19, wherein the plug-in further interfaces with one or more client computers and is configured to: receive a service call from one of the one or more client computers, the service call requesting a service provided by the deployed decision service; extract a service time from the service call; access a service catalog, the service catalog comprising a mapping of decision services currently deployed in the target managed system and respective availability periods of said decision services; call, by the business rule service package, the requested decision service if its assigned availability period according to the mapping covers the service time, and return a result of the called decision service to the client computer; and if the availability period assigned to the requested decision service does not cover the service time, deny execution of the service request. 21. A computer-implemented method, comprising: a decision service manager authenticating at a managed system, the managed system hosting a decision service; in case of a successful authentication at the managed system, the decision service manager sending a first status request to the managed system; the decision service manager receiving, in response to the first status request, a first indication of a current status of the managed system, wherein the first indication comprises a specification of resources being available at the managed system and comprises a description of each decision service being currently hosted on the managed system, wherein the resources are, in particular, available databases and respective access credentials, database tables, network cards, processors, memory, storage, bus systems, device interfaces and available program libraries; the decision service manager authenticating at a target managed system; in case of a successful authentication at the target managed system, the decision service manager sending a second status request to the target managed system; the decision service manager receiving, in response to the second status request, a second indication of a current status of the target managed system, the decision service manager outputting the second indication to a user of the decision service manager and receiving the decision service from the user, the decision service being received in a modified form, the modifications of the decision service having been implemented in accordance with a current status of the target managed system; the decision service manager performing a deployment readiness check, the check comprising comparing the first and the second indication and based upon criteria of the target managed system, including the decision services currently deployed to the target managed system, available resources at the target managed system and on requirements of the service to be deployed, the criteria including at least one of: that the decision service to be deployed does not depend on any resource not available in the target managed system; that the decision service to be deployed does not depend on any other decision service not already been deployed in the target managed system; or that the managed system responded to a request for availability by the decision service manager with an acknowledgement; and in case the deployment readiness check returns as result that the current status of the target managed system allows the target managed system to host the decision service, automatically, by a hardware processor, deploying the decision service to the target managed system, wherein deploying the decision service comprises transferring executable code and a service description file to the target managed system, wherein the executable code upon execution by the target managed system provides the deployed decision service and wherein content of the service description files of all decision services currently being deployed to the target managed system are returned as response in case the target system receives a status request from the decision service manager. |