The Visual Contract Workbench is a tool that supports model-driven development of software systems by lifting the Design by Contract idea, which is usually used at the code level, to the model level. It uses visual contracts for graphically specifying the pre- and post-conditions of an operation. Java classes with JML (Java modeling language) assertions are generated from visual contracts to facilitate automatic monitoring of the correctness of the programmers' implementation

Design by contract (DbC) is widely acknowledged to be a powerful technique for creating reliable software. DbC allows developers to specify the behavior of an operation precisely by pre- and post-conditions. Existing DbC approaches predominantly use textual representations of contracts to annotate the actual program code with assertions. In the unified modeling language (UML), the textual object constraint language (OCL) supports the specification of preand post-conditions by constraining the model elements that occur in UML diagrams. However, textual specifications in OCL can become complex and cumbersome, especially for software developers who are typically not used to OCL. In this paper, we propose to specify the pre-and post-conditions of an operation visually by a pair of UML object diagrams (visual contract). We define a mapping of visual contracts into Java classes that are annotated with behavioral interface specifications in the Java modeling language (JML). The mapping supports testing the correctness of the implementation against the specification using JML tools, which include a runtime assertion checker. Thus we make the visual contracts executable.

Web services are software components that can be discovered and employed at runtime using the Internet. Conflicting requirements towards the nature of these services can be identified. From a business perspective, Web services promise to enable the formation of ad-hoc cooperations on a global scale. From a technical perspective, a high degree of standardization and rigorous specifications are required to enable the automated integration of Web services. A suitable technology for Web services has to mediate these needs for flexibility and stability. In this paper a new approach to the description of Web service semantics is introduced. It is a visual approach based on the use of software models and graph transformations and allows for the description of innovative services while providing a precise matching concept. An implementation using current standards and tools is available.