上接：/blog/metrics_softwaremetrics2.html
Measuring Internal Product Attributes: Structure
测量产品内部属性：结构
The structure of requirements, design, and code may help the developers to understand the difficulty they sometimes have in converting one product to another, in testing a product, or in predicting external software attributes from early internal product measures, such as maintainability, testability, reusability, and reliability. 需求，设计，编码的结构可能有助于开发者明白把一个产品转换成另一个，测试一个产品，或者从一个早期内部产品的测试，预测软件外部属性，如可维护性，可测试性，可重用性，和可靠性，是有难度滴。-翻译得有点水。
The structure of a product plays a part, not only in requiring development effort but also in how the product is maintained. 产品的结构不仅在开发时对人力的需求，而且在产品的维护上也扮演了重要作用。
Types of structural measures 结构度量分类
Control-flow structure: the sequence in which instructions are executed in a program.控制流结构：指令在程序中执行的顺序。
Data-flow structure: the trail of a data item created or handled by a program. 数据流结构：一个程序中的数据项从创建到处理的轨迹。
Data structure: the organization of the data itself, independent of the program. 数据结构：数据本身的组织，独立于程序。
Control-Flow Structure
McCabe’s cyclomatic complexity measure。 McCabe环路复杂度测量。
Definition: The cyclomatic number V(G) of a graph G with n vertices, e edges, and p connected components (连通分量) is V(G) = e – n ＋ P。定义：在图G中的复杂度V（G）=……，n节点，e边，p连通分量。MaCabe #CC
Theorem: In a strongly connected graph G, the cyclomatic number is equal to the maximum number of linearly independent circuits. 理论基础：在强联通图G中，复杂度=最大线性无关线环路数。
(引用下百科：V(G)=m-n+p其中，V(G)是有向图G中环路数，m是图G中弧数，n是图G中结点数，p是图G中强连通分量个数。在一个程序中，从程序图的入口点总能到达图中任何一个结点，因此，程序总是连通的，但不是强连通的。为了使图成为强连通图，从图的入口点到出口点加一条用虚线表示的有向边，使图成为强连通图。这样就可以使用上式计算环路复杂性了。)
后面内容PPT讲得好复杂啊，都懒得去看懂。也没时间去弄懂了。我就记得有三种计算方法：把平面分成的圈数目；判定数目+1；边-定点+2；
此处省略N多PPT内容。
The cyclomatic number is a useful indicator of how difficult a program or module will be to test and maintain. When V exceeds 10 in any one module, the module may be problematic.
The module be rejected if its V exceed 20 or if it has more than 50 statements (Bennet 1994).值指示了一个模块或者程序测试或者维护时有多复杂，当任意一个模块值>=10，这个模块就有问题了，超过20时或者超过50句statements时，就应该拒绝它，重新设计。
此处引用学姐学长的资源：
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McCabe方法的计算步骤分如下三步：</p>
步骤1：将程序流程图退化成有向图，即将程序流程图的每个处理框看作一个节点，将流线看作连接各节点的有向弧。
步骤2：在有向图中，由程序出口到入口连接一条虚有向弧。
步骤3：计算V（G）=m-n＋1
其中，V（G）是有向图G中环数，m是有向图G中的弧数，n是有向图G中的节点数。
实践表明，模块规模以V(G)≤10为宜，也就是说，V(G)=10是模块规模的一个更科学更精确的上限。</td> </tr>
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原子语句（A）
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条件（C）
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循环（L）
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定序（S）
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节点数
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FA() = 2
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FC(m1,m2) = m1 + m2
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FL(m1) = m1 + 1
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Fs(m1,m2) = m1 + m2 – 1
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边数
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FA() = 1
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FC(m1,m2) =m1+ m2 + 2
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FL(m1) = m1 + 2
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Fs(m1,m2) = m1 + m2
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环形复杂度
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FA() = 0
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FC(m1,m2) = m1 + m2 + 1
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FL(m1) = m1 + 1
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FS(m1,m2) = m1 + m2
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Hences, MaCabe #CC=计算出的环形复杂度+1
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V(p)=(#Edges+1)-#Nodes+1=#Edges-#Nodes+2
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</tbody> </table>
Advantages
Provides a complexity measure of software and control flow. 为软件的控制流提供了一种复杂度量方式。
Provides a quantitative measure testing difficulty and reliability。量化了测试复杂性和可靠性。
Studies have shown a clear relationship between McCabe’s score and the number of errors and time to correct errors.研究发现McCabe 分数跟错误数和纠正错误时间有清晰的关系。
Provides a practical upper limit for module size of 10, with those that exceed this level causing problems testing the modules。提供准确的模块上限值10，超过它就会引起测试的困难。
Offers a graphical depiction of the control of flow.提供一种控制流的图形描述。
Provides a structures testing approach。提供一种结构测试途径。
Measures characteristics which are related to the size of the task.具有跟任务大小相关的度量特性。
Simple to compute and can be automated.容易计算且能够自动化应用。
Can be used to predict future maintenance effort and cost.能够用来预测将来的维护的人力和成本。
Most widely used test.广泛用来测试。
Can be computed early in life cycle than Halstead metrics.在生命周期中比Halstead度量方法更早。
Disadvantages
Context sensitive. 5 if states in one program will have the same complexity value as 5 in other.跟上下文敏感，5个if语句跟5个其他的，有相同的复杂度。
Measures only a few facets of the program.只测量了一个程序的少的几个方面。
Combining multiple metrics is likely to yield better results.需要结合多种度量方法以获取更好的结果。
Metrics is calculated too late in the software development process to be an effective management tool.在软件开发过程阶段才计算以至于不是一个有效的管理工具。
Not a good measure of complexity in data driven systems.在数据驱动的系统当中不是一个好的复杂性度量方式。
Does not take program length into consideration。没把程序长度考虑进去。
Object-oriented code can give misleading results. 面向对象的编码方式可能引起错误的结果。
Data structure
Unfortunately there has been little work in considering the amount of structure in every data item.不幸的是几乎很少有工作在每一个数据项都考虑了结构数量的。
The overall “complexity” of a system can not be depicted completely without measures of data stucture.总体来说的一个系统的复杂度不能被完成的描述，要是没有数据结构的度量的话。
Control-flow measures can fail to identify complexity when it is hidden in the data structure.控制流测量对鉴别隐藏在数据结构中的复杂度时会失效。
Boehm using D/P has derived a simple ordinal-scale measure called DATA, used as one of the COCOMO cost drivers, to measure amount of data.
Data-flow structure
未完待续……
