System Properties系統特性

系統特性(System Properties)當中有下列幾項定義，這邊介紹主要是用在效能評估上面，因為排隊理論通常就是用來解決這樣的問題，我們先定義，之後才有辦法討論。(這是參考Queueing Networks and Markov Chains: Modeling and Performance Evaluation with Computer Science Applications, 2nd Edition)

• Performance:(效能)
  The degree to which a system or component accomplishes its designated functions within given constraints, such as speed, accuracy, or memory usage.
• Reliability:(可靠性)
  The probability that the software will not cause the failure of the system for a specified time under specified condition.
• Availability:(可利用性)
  The ability of a system to perform its required function at a stated instant or over a stated period of time.
  
• Dependability:(可依賴性)
  The dependability of a computer system is the ability to deliver a service that can justifiably be trusted.
• Performability:(可執行性)
  The probability that the system reaches an accomplishment level y over a utilization interval (0,t).