Abstract
Over the past several years, the World Wide Web has emerged from a research project to an environment for open, commercial services, such as online-banking, travel reservation, and stock-trading. However, in contrast to the best-effort approach provided by the Web, many of those services demand higher predictability and quality- of-service properties such as security, end-to-end availability, dependability, and real time. The development of a systematic, architectural approach for connecting Web- interfaces to legacy systems, such as databases and transaction processing is an open research question.The Common Object Request Broker Architecture (CORBA) is a widely-accepted, standardized open system integration framework based on distributed object technologies, which has been successfully used for implementation of open Web services. CORBA is focused on facilitating general computing environments and does not explicitly address quality-of-service parameters neither for its communication links nor its endsystems. However efforts like the Real-Time CORBA Special Interest Group (SIG) at OMG and the ''pluggable protocols'' proposal will ultimately lead to support of quality-of-service properties for CORBA communication links.Within this paper we are concentrating on architectural approaches for fault-tolerant, highly available endsystems. We present the ''Observer'' approach for implementation of reliable CORBA clients. Consensus protocols based on the ''Composite Objects'' technique is our solution for constructing CORBA servers with high predictability regarding timely and reliable method execution. Our middleware uses commercial off-the-shelf (COTS) technology and aims at conversion of legacy applications into reliable Web-services.We present Java-based Web-interfaces to the ''Balancing Robots'' soft real-time simulation. Also, we demonstrate a fault-tolerant version of the Netscape Navigator based on our ''Observer'' technique.