Techniques based on formal semantics are discussed for automatically generating parallelizing compilers for object-oriented programming languages. The denotational semantics of object-oriented programming languages are used to derive the control and data dependencies that exist within programs and this information may then be used to produce parallel object code by a compiler. This approach also easily facilitates proving the correctness of transformations performed on the source programs. Furthermore, since compilers may be automatically generated from denotational semantics specifications, the implementation of these parallelization techniques will be automatic and hence language independent.

Abstract We present a compression technique for heterogeneous files, those files which contain multiple types of data such as text, images, binary, audio, or animation. The system uses statistical methods to determine the best algorithm to use in compressing each block of data in a file (possibly a different algorithm for each block). The file is then compressed by applying the appropriate algorithm to each block. We obtain better savings than possible by using a single algorithm for compressing the file. The implementation of a working version of this heterogeneous compressor is described, along with examples of its value toward improving compression both in theoretical and applied contexts. We compare our results with those obtained using four commercially available compression programs, PKZIP, Unix compress, Stufflt, and Compact Pro, and show that our system provides better space savings.

Important strides toward developing expressive yet semantically sound type systems for object-oriented programming languages have recently been made by Cook, Bruce, Mitchell, and others. This paper focusses on how the theoretical work using F-bounded quantification may be brought more into the realm of actual language implementations while preserving rigorous soundness properties. We simultaneously address three of the more significant problems: adding a notion of global state, proving type-checking is decidable, and integrating the more widely implemented view that subclasses correspond to subtypes with the F-bounded view.

A framework for generating testing preorders that relate processes on the basis of their timing behavior as well as their degree of relative nondeterminism is developed. The basic concepts of transition systems and testing are reviewed, and timed testing, which takes account of the delay exhibited by a process as it attempts to pass a test, is introduced. The framework is then applied to two different scenarios. In the first, relations are constructed that relate processes on the basis of all timing considerations. In the second, relations are constructed that relate processes on the basis of their relative speeds. In both cases, alternative denotational characterizations of the resulting preorders are presented, and examples are given to illustrate the utility of the approach.>