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Show 15 To summarize, a suitable formal model of monitoring must provide: • a uniform description of states and steps, • the degree of similarity between states. The calculus of delta sets was devised to meet these requirements. 2.2.1 Prerequisites A program is a sequence of instructions that are intended for execution on an interpreter. The interpreter can be implemented in hardware as a real computer or in software as a virtual machine. A program executed by the interpreter is called a process. A process state consists of program instructions, program data, and the interpreter state. At any given moment during the execution, a process is determined by its state. The execution of a program is a sequence of process states. Assuming that programs are sequential, the execution proceeds in steps. A step is an atomic transition between two successive states. Introspection involves two processes, an executor and a director. The executor can be any executing computer program. The director is able to perform two types of actions related to the executor: monitoring and controlling. Monitoring is the gathering of data about the executor. Controlling is the modification of the state of the executor. 2.2.2 Calculus o f Delta Sets D e finition 1 (D e lta Set) A delta set is a set of pairs. Each pair consists o f two components, an address and a value. Each address in a delta set occurs in at most one pair. |
