Prefetching techniques for client server object-oriented database systems

The performance of many object-oriented database applications suffers from the page fetch latency which is determined by the expense of disk access. In this work we suggest several prefetching techniques to avoid, or at least to reduce, page fetch latency. In practice no prediction technique is perfect and no prefetching technique can entirely eliminate delay due to page fetch latency. Therefore we are interested in the trade-off between the level of accuracy required for obtaining good results in terms of elapsed time reduction and the processing overhead needed to achieve this level of accuracy. If prefetching accuracy is high then the total elapsed time of an application can be reduced significantly otherwise if the prefetching accuracy is low, many incorrect pages are prefetched and the extra load on the client, network, server and disks decreases the whole system performance. Access pattern of object-oriented databases are often complex and usually hard to predict accurately. The ..

VOODB: A Generic Discrete-Event Random Simulation Model to Evaluate the Performances of OODBs

International audiencePerformance of object-oriented database systems (OODBs) is still an issue to both designers and users nowadays. The aim of this paper is to propose a generic discrete-event random simulation model, called VOODB, in order to evaluate the performances of OODBs in general, and the performances of optimization methods like clustering in particular. Such optimization methods undoubtedly improve the performances of OODBs. Yet, they also always induce some kind of overhead for the system. Therefore, it is important to evaluate their exact impact on the overall performances. VOODB has been designed as a generic discrete-event random simulation model by putting to use a modelling approach, and has been validated by simulating the behavior of the O2 OODB and the Texas persistent object store. Since our final objective is to compare object clustering algorithms, some experiments have also been conducted on the DSTC clustering technique, which is implemented in Texas. To validate VOODB, performance results obtained by simulation for a given experiment have been compared to the results obtained by benchmarking the real systems in the same conditions. Benchmarking and simulation performance evaluations have been observed to be consistent, so it appears that simulation can be a reliable approach to evaluate the performances of OODBs

On the classification and evaluation of prefetching schemes

Abstract available: p. [2

Object-Oriented Software Representation of Polymer Materials Information in Engineering Design

The software application POISE, Polymer Objects in a Smalltalk™ Environment, integrates knowledge representation, user interfaces, and data management; a system of tools for the materials domain expert involved in design. Engineering design solutions initially build from generalisations. POISE represents multiple levels of generalisations from classifications of polymer information. The class-instance paradigm classifies software objects. An object’s behaviour is an exclusive function of its class. Polymer’s behaviours are a function of multiple orthogonal factors, like chemistry and processing, therefore multiple orthogonal classes must represent polymers. Taxonomy only represents one of these factors. The Enhancer mechanism resolves this conflict between classification and representation. Polymer classification is not well established, with new materials evolving. The software compensates by evolving the classification schema. Guided with a specialised interface tool, the domain expert updates the schema by adding new polymer families and re-classifying existing classes. Through analysing the generalisations in the classification, the domain expert can develop an appropriate classification. This analysis relies on the engineering properties differentiating the principal material qualities. Standard properties do not distinguish specific structural differences in polymer materials, necessitating new properties. Material properties distinguish materials in the domain whereas the classes describe the properties of polymer objects. Domain experts add new properties to the polymer classes to distinguish polymer objects. Properties are independent objects that partially describe the class template; Partial Template Objects. Persistence of personal design information and management of shared data requires dichotomous database management. Shared data requires multi-user access, and consequently transaction management. Transaction management in object-oriented systems often holds resources for a long duration. Transaction declaration hinders transparent access to storage, and corrupts the representation. For single-user design information, transactions are implicit with access. Database proxies provide transparent per-object transaction management to persistent design information. The WorkBase is an object-storage utility that utilises Enhancers as proxies