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试题三 论软件可靠性设计技术的应用 随着软件的日益普及,系统中软件成分不断增加,使得系统对软件的依赖越来越强。软件的可靠性对系统可靠性的影响越来越大。而实践证明,保障软件可靠性最有效、最经济、最重要的手段是在软件设计阶段采取措施进行可靠性控制,为此提出了软件可靠性设计的概念。 软件可靠性设计就是在常规的软件设计中,应用各种方法和技术,使软件设计在兼顾用户功能和性能需求的同时,全面满足软件的可靠性要求。软件可靠性设计应和软件的常规设计紧密结合,贯穿于软件设计过程的始终。 请围绕“软件可靠性设计技术的应用”论题,依次从以下三个方面进行论述。

阐述你在具体的可靠性设计工作中,为了分析影响软件可靠性的主要因素,所采用的可靠性分析方法。

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阐述你在具体的可靠性设计工作中,为了分析影响软件可靠性的主要因素,所采用的可靠性分析方法。 在软件可靠性设计之前和软件可靠性设计过程中,都需要采用软件可靠性分析和预测方法,来确定当前系统中的主要可靠性因素和目标。常见的软件可靠性分析方法包括故障树分析方法、失效模式与效应分析方法等。 故障树分析方法:一种自顶向下的软件可靠性分析方法,即从软件系统不希望发生的事件(顶事件),特别是对人员和设备的安全及可靠性产生重大影响的事件开始,向下逐步追查导致顶事件发生的原因,直至基本事件(底事件),从而确定软件故障原因的各种可能组合方式和(或)发生概率。基本的步骤是软件故障树的建立、定性分析和定量分析。 失效模式与效应分析方法:在软件开发阶段的早期,通过识别软件失效模式,分析造成的后果,研究分析各种失效模式产生的原因,寻找消除和减少其有害后果的方法,以便尽早发现潜在的问题,并采取相应的措施,从而提高软件的可靠性和安全性。SFMEA的分析对象可以是开发早期阶段的高层次的子系统、部件,也可以是详细设计阶段的单元、模块。对于不同的分析对象,其软件失效模式是不同的,采用的SFMEA分析方法也不同,前者采用系统级分析方法(system FMEA),后者为详细级分析方法(detailedFMEA)。其基本的步骤是系统定义、软件失效模式分析、软件失效原因分析、软件失效影响分析、改进措施分析。 (结合实际工作,具体阐述自己所采用的一种或多种可靠性分析方法)论题四论分布式存储系统架构设计)

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In most parts of the world, climate change is a worrying subject. Not so in California. At a recent gathering of green luminaries—in a film star’s house, naturally, for that is how seriousness is often established in Los Angeles—the dominant note was self-satisfaction at what the state has already achieved. And perhaps nobody is more complacent than Arnold Schwarzenegger. Unlike A1 Gore, a presidential candidate turned prophet of environmental doom, California’s governor sounds cheerful when talking about climate change. As well he might: it has made his political career.

Although California has long been an environmentally-conscious state, until recently greens were concerned above all with smog and redwood trees. "Coast of Dreams", Kevin Stag’s authoritative history of contemporary California, published in 2004, does not mention climate change. In that year, though, the newly-elected Mr. Schwarzenegger made his first tentative call for western states to seek alternatives to fossil fuels. Gradually he noticed that his efforts to tackle climate change met with less resistance, and more acclaim, than just about all his other policies. These days it can seem as though he works on nothing else.

Mr. Schwarzenegger’s transformation from screen warrior to eco-warrior was completed last year when he signed a bill imposing legally-enforceable limits on greenhouse—gas emissions—a first for America. Thanks mostly to its lack of coal and heavy industry, California is a relatively clean state. If it were a country it would be the world’s eighth-biggest economy, but only its 16th-biggest polluter. Its big problem is transport—meaning, mostly, cars and trucks, which account for more than 40% of its greenhouse-gas emissions compared with 32% in America as a whole. The state wants to ratchet down emissions limits on new vehicles, beginning in 2009. Mr. Schwarzenegger has also ordered that, by 2020, vehicle fuel must produce 10% less carbon: in the production as well as the burning, so a simple switch to corn-based ethanol is probably out.

Thanks in part to California’ s example, most of the western states have adopted climate action plans. When it comes to setting emission targets, the scene can resemble a posedown at a Mr. Olympia contest. Arizona’s climate-change scholars decided to set a target of cutting the state’s emissions to 2000 levels by 2020. But Janet Napolitano, the governor, was determined not to be out-muscled by California. She has declared that Arizona will try to return to 2000 emission levels by 2012.

California has not just inspired other states; it has created a vanguard that ought to be able to prod the federal government into per national standards than it would otherwise consider. But California is finding it easier to export its policies than to put them into practice at home. In one way, California’ s self-confidence is fully justified. It has done more than any other state—let alone the federal government—to fix America’s attention on climate change. It has also made it seem as though the problem can be solved. Which is why failure would be such bad news. At the moment California is a beacon to other states. If it fails, it will become an excuse for inaction.

Janet Napolitano is mentioned in the passage to show that()

A. Arizona is determined to out-muscle California

B. female governors often set unrealistic goals

C. Arizona will start a Mr. Olympia contest with California

D. California’s actions have produced some positive effects