A fault tolerant access to legacy database systems using CORBA technology

摘要

This work presents a software-implemented fault tolerance approach for building a reliable database application in a CORBA environment. Database applications have functional requirements and non-functional requirements, such as dependability and performance. We provide an architectural framework that makes it possible to separately address these issues. More precisely, it is possible to: i) guarantee functional properties by incorporating existing software modules, and ii) add dependability to the resulting system via proper programming of the business logic of the Middle Tier. The legacy software is integrated in the new system with no changes. This strategy can effectively reduce the development effort for building a reliable system, while protecting the investment in legacy applications. First, code writing activity is minimized, since system functions are implemented via reuse of existing software. Second, system testing activity is reduced, since only reliability-related functions and interactions between individual components need to be tested. A system prototype has been developed and evaluated. The prototype incorporates a legacy application and replicates it according to a Triple Modular Redundancy (TMR) scheme. Experiments demonstrated system dependability was significantly improved.