Another concept of Third Eye is the tracing state. Tracing state is a set of event types generated in that state, other event types are filtered out and not reported. The system is always in a specific tracing state. Tracing states correspond to specifications. A program specification describes a set of constraints on events. The event types used in a specification have to be monitored to validate a trace against this specification. All event types contained in a specification and monitored for this specification form a tracing state. Tracing states also control the overhead of tracing on the executing system.The Third Eye framework includes modules for event type definition, event generation and reporting, tracing state definition and management, trace logging, query and browsing interfaces. Modules of event type definition, event reporting facility and tracing state controler are integrated with the software of the system under trace (SUT). The rest of the modules are independent from the SUT and can be deployed on a different execution platform to minimize the influence on system performance. Trace delivery for logging and analysis uses alternative interfaces to accommodate devices with different data storage and connectivity capabilities. We have implemented Third Eye framework prototype currently used by the Third Eye project team in collaboration with product development teams in Nokia's business units. We used Third Eye to test a number of software systems: the memory subsystem of one of Nokia's handsets, Apache Web Server, and WAP (Wireless Application Protocol) client. WAP is an industrial standard for applications and services that operate over wireless communication networks. We validated message sequences in this protocol by adding events in the functions that correspond to the protocol primitives and then checking whether the event sequence corresponds to the protocol message sequence. Events are mapped to Prolog facts and constraints are expressed as Prolog rules. Third Eye can be used for debugging, monitoring, specification validation, and performance measurements. These scenarios use typed events—a concept simple and yet expressive enough to be shared by product designers and developers. The Third Eye has an open architecture allowing easy replacement of third-party tools, including databases, analysis and validation tools. Third Eye is a practical framework for specification-based analysis and adaptive execution tracing of software systems.