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Abstract The advantages of virtual machine (VM) execution (dynamically loaded, portable object files with high-level information) also permit changing the semantics of executables. Load-time adaptation (LTA) intercepts the VM’s file operations and modifies object code on the fly, without changing the VM implementation, without needing access to source code, and without changing the actual files. We introduce a new technique, library-based LTA, and show how it can extend languages in such ways as adding contracts or mixins to existing classes, providing default code for interfaces, and instantiating parameterized types. We discuss an implementation of library-based LTA and its application to extending Java semantics. 1.

interpretation is commonly used as a program analysis tool to provide optimization information at compile time, and not to enhance programmer understanding. Many programmers might not find information such as the strictness or mode of parameters to be useful for program comprehension, testing or debugging tasks. The method of propagating assertions outlined here is not intended to improve execution speed, but to improve (end-user) programmer understanding, and program correctness. By involving the user in the specification of the initial assertions, we hope to derive information that is useful to the user, as opposed to the computer.

Abstract — Web services are emerging as a key infrastructure for providing inter-operation between applications and systems and for providing support for the deployment of e-commerce business processes. One important issue for ensuring the growth of Web services is having ways of describing the available Web services in a precise way. One possible step toward providing semantic information for Web services is through the use of formal contract specification—that is, using pre/post-conditions. We present a number of ways in which pre/post-conditions could be introduced into Web services descriptions, for specification as well as dynamic verification purpose. The use of pre/post-conditions, however, is not sufficient to describe the semantic of a group of related operations, for example, to describe the legal sequences in which these operations can/should be used. Although business process description languages like BPEL4WS or WSCI can express such descriptions, these are procedural descriptions, not necessarily appropriate for specification purpose. We present one possible way in which such descriptions could be provided for Web services, using path expressions that can show the order in which the various operations of a Web service can and should be invoked. Static and dynamic uses of these protocol specifications are then described. I.

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