Existing web proxy caches employ cache consistency mechanisms to ensure that locally cached data is consistent with that at the server. In this paper, we argue that techniques for maintaining consistency of individual objects are not sufficient-a proxy should employ additional mechanisms to ensure that related web objects are mutually consistent with one another. We formally define the notion of mutual consistency and the semantics provided by a mutual consistency mechanism to end-users. We then present techniques for maintaining mutual consistency in the temporal and value domains. A novel aspect of our techniques is that they can adapt to the variations in the rate of change of the source data, resulting in judicious use of proxy and network resources. We evaluate our approaches using real-world web traces and show that (i) careful tuning can result in substantial savings in the network overhead incurred without any substantial loss in fidelity of the consistency guarantees, and (ii) the incremental cost of providing mutual consistency guarantees over mechanisms to provide individual consistency guarantees is small.

Abstract

Health care professionals rely on software to simulate anatomical and physiological elements of the human body for purposes of training, prototyping, and decision making. Software can also be used to simulate medical processes and protocols to measure cost effectiveness and resource utilization. Whereas much of the software engineering research into simulation software focuses on validation (determining that the simulation accurately models real-world activity), to date there has been little investigation into the testing of simulation software itself, that is, the ability to effectively search for errors in the implementation. This is particularly challenging because often there is no test oracle to indicate whether the results of the simulation are correct. In this paper, we present an approach to systematically testing simulation software in the absence of test oracles, and evaluate the effectiveness of the technique.

Cryptographic hash functions are security-critical algorithms with many practical applications, notably in digital signatures. Developing an approach to test them can be particularly difficult, and bugs can remain unnoticed for many years. We revisit the NIST hash function competition, which was used to develop the SHA-3 standard, and apply a new testing strategy to all available reference implementations. Motivated by the cryptographic properties that a hash function should satisfy, we develop four tests. The Bit-Contribution Test checks if changes in the message affect the hash value, and the Bit-Exclusion Test checks that changes beyond the last message bit leave the hash value unchanged. We develop the Update Test to verify that messages are processed correctly in chunks, and then use combinatorial testing methods to reduce the test set size by several orders of magnitude while retaining the same fault-detection capability. Our tests detect bugs in 41 of the 86 reference implementations submitted to the SHA-3 competition, including the rediscovery of a bug in all submitted implementations of the SHA-3 finalist BLAKE. This bug remained undiscovered for seven years, and is particularly serious because it provides a simple strategy to modify the message without changing the hash value returned by the implementation. We detect these bugs using a fully-automated testing approach.

This paper describes an approach to the management of resources. The paper suggests that a resource should be viewed as a provider of a set of capabilities, where that set may vary over time and with circumstances. This view of resources is defined and then made the basis for the architecture of a system for storing, managing, and assigning resources. The ROMEO prototype resource management system is presented as an example of how this architecture can be instantiated. Some case studies of the use of ROMEO are presented and used to evaluate the architecture, the ROM-EO prototype, and our view of the nature of resources.