An SDL pattern is a reusable software artifact representing a generic solution for a recurring design problem. It is required that SDL be the applied design language. Thereby we benefit from the formal basis provided by SDL. Instead of specifying and applying the patterns rather informally, a formal target language such as SDL offers the possibility of precisely specifying how to apply a specific pattern, under which assumptions this will be allowed, and what properties result for the embedding context. In the paper we discuss aspects of tool support for SDL-pattern application. In particular, we describe requirements, design decisions, and some implementation issues of a prototype SDL-pattern editor that is currently under development. The SDL-pattern editor mainly supports syntactical application and documentation of SDL patterns.

In 1988, a formal semantics for SDL has been added as Annex F to the Z.100 SDL standard [5,6,7,8]. Along with the efforts to improve SDL, the semantics has been revised several times since then. To understand the semantics, intimate knowledge of the language Meta IV is required. Meta IV is a formal language based on synchronous communication between a set of concurrent processes. Essentially, Annex F defines a sequence of Meta IV programs that take an SDL specification as input, determine the correctness of its static semantics, perform a number of transformations to replace several language constructs, and interpret the specification. It has been argued that this style of defining the formal semantics is particularly suitable for tool builders. With the ongoing work to improve SDL, and a new version called SDL-2000 to pass the standardization bodies shortly, it has become apparent that a decision concerning the SDL semantics needs to be taken. One alternative is to revise the existing SDL semantics, which has the advantage of continuity. Another alternative currently under consideration is to redo the SDL semantics, which offers an opportunity for improvement. In this paper, some of the choices that go along with a new definition of a formal SDL semantics are presented and discussed. Based on the results of this discussion, a coarse outline for a new formal semantics is proposed.

Structural synthesis is one of the most important tasks in the creative design of mechanisms. In the past decades, spatial parallel mechanisms have been extensively synthesized. However, structural synthesis of more complex spatial mechanisms with coupling chains is seldom addressed. This paper aims to propose a general method for synthesizing a class of important spatial mechanisms with coupling chains, called two-layer and two-loop (TLTL) mechanisms, which are the basic units for constructing multi-layer and multi-loop mechanisms with more complex couplings. First, the motion screw equation of TLTL mechanisms is derived, with which mobility or degree-of-freedom (DOF) of the class of mechanisms can be analyzed and rigid substructures can be detected. Then, a general method for structural synthesis of TLTL mechanisms is proposed on the basis of the principle of mobility analysis. Finally, TLTL mechanisms with fourteen kinds of degrees of freedom are synthesized, illustrating the effectiveness of the method.