1. A computer-implemented method of modifying an existing standard-based system comprising: displaying within a presentation layer, at runtime of the standard-based system, representations of a client of the standard-based system, a Web-based service providing services to the client, and message types exchanged between the client and the Web-based service comprising a service request sent from the client to the Web- based service and a service response sent from the Web-based service to the client; responsive to a user input selecting at least one message type received within the presentation layer, associating a constraint with the selected message type of the standard-based system at runtime, wherein the constraint specifies a limitation upon information that is requested within a service request or a limitation upon information that is provided within a service response, wherein the limitation upon information that is requested within a service request or the limitation upon information that is provided within a service response is not available within the standard-based system; intercepting a message of the selected type that is exchanged between the client and the Web-based service; applying the constraint by modifying content of the message according to the constraint, wherein applying the constraint comprises: when the intercepted message corresponds to a service request type of message, modifying at least one parameter of the message to conform with the limitation specified by the constraint after the service request is sent from the client and prior to the service request being received by the Web-based service; when the intercepted message corresponds to a service response type of message, modifying data within the message to conform with the limitation specified by the constraint after the service response is sent from the Web-based service and prior to the service response being received by the client; and storing the message.