Merge pull request #412 from repzy/metrics-file

Add metrics description file

Author: Halleck45

README.md

@@ -31,6 +31,10 @@ Then open the generated `./myreport/index.html` file in your browser.
 
 If want, you can [install](https://github.com/phpmetrics/PhpMetrics/blob/master/doc/installation.md) PhpMetrics globally with your favorite package manager. You can also visit our [documentation](http://www.phpmetrics.org/documentation/index.html).
 
+## Metrics list
+
+See the [metrics](doc/metrics.md) file.
+
 ## Author
 
 + Jean-François Lépine <[@Halleck45](https://twitter.com/Halleck45)>

doc/metrics.md

@@ -0,0 +1,168 @@
+# List of available metrics
+
+## Halstead complexity measures 
+### Metrics: 
+length, vocabulary, volume, difficulty, effort, level, bugs, time, intelligentContent, number_operators, number_operands, number_operators_unique, number_operands_unique    
+
+### Description
+
+**n1** = the number of distinct operators      
+**n2** = the number of distinct operands      
+**N1** = the total number of operators      
+**N2** = the total number of operands      
+    
+From these numbers, eight measures can be calculated:      
+    
+**Program vocabulary:** n = n1 + n2      
+**Program length:** N = N1 + N2      
+**Calculated program length:** N' = n1 * log2(n1) + n2 * log2(n2)      
+**Volume:** V = N * log2(n)        
+**Difficulty:** D = (n1/2) * (N2/n2)        
+**Effort:** E = D * V      
+**Time required to program:** T = E / 18 seconds      
+**Number of delivered bugs:** B = V / 3000
+
+### Links     
+[https://en.wikipedia.org/wiki/Halstead_complexity_measures](https://en.wikipedia.org/wiki/Halstead_complexity_measures)
+[https://www.verifysoft.com/en_halstead_metrics.html](https://www.verifysoft.com/en_halstead_metrics.html)
+    
+## Cyclomatic complexity number and weighted method count 
+### Metrics: 
+wmc, ccn, ccnMethodMax
+    
+### Description
+The cyclomatic complexity (CCN) is a measure of control structure complexity of a function or procedure.    
+We can calculate ccn in two ways (we choose the second):    
+    
+1. Cyclomatic complexity (CCN) = E - N + 2P    
+  Where:    
+  P = number of disconnected parts of the flow graph (e.g. a calling program and a subroutine)    
+  E = number of edges (transfers of control)    
+  N = number of nodes (sequential group of statements containing only one transfer of control)    
+    
+2. CCN = Number of each decision point    
+    
+The weighted method count (WMC) is count of methods parameterized by a algorithm to compute the weight of a method.    
+Given a weight metric w and methods m it can be computed as    
+    
+sum m(w') over (w' in w)    
+    
+Possible algorithms are:    
+    
+- Cyclomatic Complexity    
+- Lines of Code    
+- 1 (unweighted WMC)    
+    
+This visitor provides two metrics, the maximal CCN of all methods from one class (currently stored as ccnMethodMax)    
+and the WMC using the CCN as weight metric (currently stored as ccn).    
+
+### Links
+[https://en.wikipedia.org/wiki/Cyclomatic_complexity](https://en.wikipedia.org/wiki/Cyclomatic_complexity)    
+[http://www.literateprogramming.com/mccabe.pdf](http://www.literateprogramming.com/mccabe.pdf)    
+[https://www.pitt.edu/~ckemerer/CK%20research%20papers/MetricForOOD_ChidamberKemerer94.pdf](https://www.pitt.edu/~ckemerer/CK%20research%20papers/MetricForOOD_ChidamberKemerer94.pdf)    
+     
+## Kan's defects 
+### Metrics: 
+kanDefect    
+
+### Description
+**kanDefect** = 0.15 + 0.23 *  number of do…while() + 0.22 *  number of switch() + 0.07 * number of if()    
+
+### Links
+    
+## Maintainability Index 
+### Metrics: 
+mi, mIwoC, commentWeight    
+
+### Description
+    
+According to Wikipedia, "Maintainability Index is a software metric which measures how maintainable (easy to support and change) the source code is. The maintainability index is calculated as a factored formula consisting  of Lines Of Code, Cyclomatic Complexity and Halstead volume."    
+    
+mIwoC: Maintainability Index without comments    
+MIcw: Maintainability Index comment weight    
+mi: Maintainability Index = MIwoc + MIcw    
+    
+**MIwoc** = 171 - 5.2 * ln(aveV) -0.23 * aveG -16.2 * ln(aveLOC)    
+**MIcw** = 50 * sin(sqrt(2.4 * perCM))    
+**mi** = MIwoc + MIcw    
+
+### Links
+
+[https://www.verifysoft.com/en_maintainability.html](https://www.verifysoft.com/en_maintainability.html)
+ 
+    
+## Lack of cohesion of methods 
+### Metrics: 
+lcom    
+ 
+### Description   
+
+Cohesion metrics measure how well the methods of a class are related to each other. A cohesive class performs one function while a non-cohesive class performs two or more unrelated functions. A non-cohesive class may need to be restructured into two or more smaller classes.    
+High cohesion is desirable since it promotes encapsulation. As a drawback, a highly cohesive class has high coupling between the methods of the class, which in turn indicates high testing effort for that class.    
+Low cohesion indicates inappropriate design and high complexity. It has also been found to indicate a high likelihood of errors. The class should probably be split into two or more smaller classes.    
+
+### Links
+[https://blog.ndepend.com/lack-of-cohesion-methods/](https://blog.ndepend.com/lack-of-cohesion-methods/)
+[http://www.arisa.se/compendium/node116.html](http://www.arisa.se/compendium/node116.html)
+    
+## Card and Agresti metric 
+### Metrics 
+relativeStructuralComplexity, relativeDataComplexity, relativeSystemComplexity, totalStructuralComplexity, totalDataComplexity, totalSystemComplexity    
+  
+### Description 
+Fan-out = Structural fan-out = Number of other procedures this procedure calls    
+    
+v = number of input/output variables for a procedure    
+    
+(SC) Structural complexity = fan-out^2    
+(DC) Data complexity = v / (fan-out + 1)  
+  
+### Links  
+[https://www.witpress.com/Secure/elibrary/papers/SQM94/SQM94024FU.pdf](https://www.witpress.com/Secure/elibrary/papers/SQM94/SQM94024FU.pdf)
+
+## Length 
+### Metrics: 
+cloc, loc, lloc    
+
+### Description
+
+**loc:** lines count      
+**cloc:** lines count without multiline comments    
+**lloc:** lines count without empty lines    
+
+### Links
+    
+## Methods 
+### Metrics: 
+nbMethodsIncludingGettersSetters, nbMethods, nbMethodsPrivate, nbMethodsPublic, nbMethodsGetter, nbMethodsSetters    
+    
+## Coupling 
+### Metrics: 
+afferentCoupling, efferentCoupling, instability    
+
+### Description
+    
+**Afferent couplings (Ca):** The number of classes in other packages that depend upon classes within the package is an indicator of the package's responsibility.    
+**Efferent couplings (Ce):** The number of classes in other packages that the classes in a package depend upon is an indicator of the package's dependence on externalities.    
+**Instability (I):** The ratio of efferent coupling (Ce) to total coupling (Ce + Ca) such that I = Ce / (Ce + Ca).    
+
+### Links
+[https://www.future-processing.pl/blog/object-oriented-metrics-by-robert-martin/](https://www.future-processing.pl/blog/object-oriented-metrics-by-robert-martin/)
+[https://en.wikipedia.org/wiki/Software_package_metrics](https://en.wikipedia.org/wiki/Software_package_metrics)
+    
+## Depth of inheritance tree 
+### Metrics: 
+depthOfInheritanceTree    
+
+### Description
+Measures the length of inheritance from a class up to the root class.
+
+### Links    
+    
+## Page rank 
+### Metrics: 
+pageRank
+
+### Description
+
+### Links