On Competitive On-Line Paging with Lookahead

This paper studies two methods for improving the competitive efficiency of on-line paging algorithms: in the first, the on-line algorithm canuse more pages; in the second, it is allowed to have a look-ahead, or inother words, some partial knowledge of the future. The paper considers anew measure for the look-ahead size as well as Young's resource-boundedlook-ahead and proves that both measures have the attractive propertythat the competitive efficiency of an on-line algorithm with k extra pagesand look-ahead l depends on k+l. Hence, under these measures, an on-linealgorithm has the same benefit from using an extra page or knowing anextra bit of the future

On Competitive On-Line Paging with Lookahead

This paper studies two methods for improving the competitive efficiency of on-line paging algorithms: in the first, the on-line algorithm canuse more pages; in the second, it is allowed to have a look-ahead, or inother words, some partial knowledge of the future. The paper considers anew measure for the look-ahead size as well as Young's resource-boundedlook-ahead and proves that both measures have the attractive propertythat the competitive efficiency of an on-line algorithm with k extra pagesand look-ahead l depends on k+l. Hence, under these measures, an on-linealgorithm has the same benefit from using an extra page or knowing anextra bit of the future

Topological Aspects of Traces

This paper is a little mathematical study of some models of concurrency. The most elementary one is the concept of an independence structure, which is nothing but a set L with a binary, irreflexive and symmetric relation on it, the independence relation. This leads to the notion of a trace: a string of elements of L, modulo the equivalence generated by swapping adjacent, independent elements of the string. There are two aspects of finite traces: they form an order, hence a topology; on the other hand they form a monoid, a quotient of the free monoid on L. Unfortunately, these two points of view are hard to bring together, since the monoid structure can never be continuous or even order-preserving. It is therefore not surprising that many papers on trace theory consist of two, disjoint, parts. In this paper I concentrate on the order-theoretic and topological aspects

Automated Logical Verification based on Trace Abstractions

We propose a new and practical framework for integrating the behavioralreasoning about distributed systems with model-checking methods.Our proof methods are based on trace abstractions, which relate thebehaviors of the program and the specification. We show that for finite-statesystems such symbolic abstractions can be specified conveniently inMonadic Second-Order Logic (M2L). Model-checking is then made possibleby the reduction of non-determinism implied by the trace abstraction.Our method has been applied to a recent verification problem by Broyand Lamport. We have transcribed their behavioral description of a distributedprogram into temporal logic and verified it against another distributedsystem without constructing the global program state space. Thereasoning is expressed entirely within M2L and is carried out by a decisionprocedure. Thus M2L is a practical vehicle for handling complex temporallogic specifications, where formulas decided by a push of a button are aslong as 10-15 pages

Specification and Automated Verification of Real-Time Behaviour —A Case Study

In this paper we sketch a method for specification and automaticverification of real-time software properties. The method combinesthe IEC 848 norm and the recent specification techniques TCCS (TimedCalculus of Communicating Systems) and TML (Timed Modal Logic) - supported by an automatic verification tool, Epsilon. The methodis illustrated by modelling a small real-life steam generator example andsubsequent automated analysis of its properties.Keywords: Control system analysis; formal specification; formal verification; real-time systems; standards

Combining request scheduling with web caching

We extend the classic paging model by allowing reordering of requests under the constraint that a request is delayed by no longer than a predetermined number of time steps. We first give a dynamic programming algorithm to solve the offline case. Then we give tight bounds on competitive ratios for the online case. For caches of size k, we obtain bounds of k + O(1) for deterministic algorithms and Theta(log k) for randomized algorithms. We also give bounds for the case where either the online or the offline algorithm can reorder the requests, but not both. Finally, we extend our analysis to the case where pages have different sizes

Axiomatizing Prefix Iteration with Silent Steps

Prefix iteration is a variation on the original binary version of the Kleene star operation P*Q, obtained by restricting the first argument to be an atomic action. The interaction of prefix iteration with silent steps is studied in the setting of Milner's basic CCS. Complete equational axiomatizations are given for four notions of behavioural congruence over basic CCS with prefix iteration, viz. branching congruence, eta-congruence, delay congruence and weak congruence. The completeness proofs for eta-, delay, and weak congruence are obtained by reduction to the completeness theorem for branching congruence. It is also argued that the use of the completeness result for branching congruence in obtaining the completeness result for weak congruence leads to a considerable simplification with respect to the only direct proof presented in the literature. The preliminaries and the completeness proofs focus on open terms, i.e. terms that may contain process variables. As a by-product, the omega-completeness of the axiomatizations is obtained as well as their completeness for closed terms. AMS Subject Classification (1991): 68Q10, 68Q40, 68Q55.CR Subject Classification (1991): D.3.1, F.1.2, F.3.2.Keywords and Phrases: Concurrency, process algebra, basic CCS, prefix iteration, branching bisimulation, eta-bisimulation, delay bisimulation, weak bisimulation, equational logic, complete axiomatizations

Adaptive Physical Design for Curated Archives

We introduce AdaptPD, an automated physical design tool that improves database performance by continuously monitoring changes in the workload and adapting the physical design to suit the incoming workload. Current physical design tools are offline and require specification of a representative workload. AdaptPD is “always on” and incorporates online algorithms which profile the incoming workload to calculate the relative benefit of transitioning to an alternative design. Efficient query and transition cost estimation modules allow AdaptPD to quickly decide between various design configurations. We evaluate AdaptPD with the SkyServer Astronomy database using queries submitted by SkyServer’s users. Experiments show that AdaptPD adapts to changes in the workload, improves query performance substantially over offline tools, and introduces minor computational overhead