With current trends towards more complex software system and use of higher level languages, a monitoring technique is of increasing importance for the areas such as performance enhancement, dependability, correctness checking and so on. In this paper, we present a formal specification-based online monitoring technique. The key idea of our technique is to build a linking system, which connects a specification animator and a program debugger. The required information about dynamic behaviors of

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... formal specification and concrete implementation of a target system is obtained from the animator and the debugger. Based on those information, the judgement on the consistency of the concrete implementation with the formal specification will be provided. Not embedding any instrumentation code into the target system, our monitoring technique will not alter the dynamic behavior of the target system. Animating the formal specification, rather than annotating the target system with extra formal specifications, our monitoring technique separates the implementation-dependent description of the monitored objects and the formal requirement specification of them.