Manuel Pichler

This should be the final beta release for PHP_Depend 0.8.0. Beside some minor bugfixes, it contains a last API change for the log sub component. This change removes constraints to the ctor signature of a logger implementation, which is now part of a separate interface.

The following list shows all changes in this version. A detailed description of all issues can be found in the PHP_Depend issue tracker!

• #29 Tooltip for the Overview Pyramid.
• #34 Support for pattern based package filter.
• #37 Remove Logger - XML Config dependency.
• #38 The Logger interface should not force a default ctor-signature.

As always you can use PHP_Depend's pear channel or its svn repository, to check out this new version. And feel free to discuss and follow the PHP_Depend development on its dedicated mailing list.

The Overview Pyramid is used to visualize a complete software system in a really compact manner. Therefor it collects a set of metrics from the categories Inheritance, Coupling and Size & Complexity, and puts them into relation. The following figure shows the base structure of the Overview Pyramid[ML06].

Base structure of the Overview Pyramid.

Metrics used by the Overview Pyramid

The following three lists contain all the metrics, which the Overview Pyramid uses.

Size and Complexity

The category Size & Complexity contributes the greatest and mostly used set of software metrics.

NOP

The Number Of Packages metric counts the packages within the analyzed software system.

NOC

The Number Of Classes metric counts the declared classes within the analyzed software system.

NOM

The Number Of Methods metric counts all declared methods, which in this context means class methods and simple functions.

LOC

The Lines Of Code metric shows the number of executable source lines within the analyzed software system. To calculate this value PHP_Depend counts all non whitespace lines and all non comment lines.

CYCLO

Cyclomatic complexity is a software metric (measurement). It was developed by Thomas McCabe and is used to measure the complexity of a program. It directly measures the number of linearly independent paths through a program's source code.

Source: Wikipedia

Coupling

This group of metrics informs about the coupling between different program parts in the analyzed application.

CALLS

This metric count the number of distinct function- and method-calls. Distinct means that one and the same method-call within a function- or method-body is only counted once.

FANOUT

The FANOUT provides information on types referenced by classes and interfaces. It only counts those types that are not part of the same Inheritance branch.

Inheritance

Both metrics in this group deal with the use of Inheritance and give a general overview of the use of Inheritance within the analyzed system.

ANDC

The Average Number of Derived Classes metric describes the average of derived classes. In a system of ten classes an ANDC-value of 0.5 means, that every second class is derived from another class.

AHH

The Average Hierarchy Height metric is a average depth of the inheritance hierarchy. In a system of ten classes, a AHH-value of 1 can be interpreted in different ways, for example: Five classes inherit from five other classes within the analyzed application or five classes inherit from a single root class.

Structure of the Overview Pyramid

Now that we know all metrics used for the Overview Pyramid, it is time to replace the placeholders with the measured informations. The figure below shows the filled Overview Pyramid.

The filled Overview Pyramid

In a second step, the previously independent metrics are set into relation. Therefor we calculate the average values of individual value pairs, these computed values provide us with new informations about the distributions within the application.

The following example figure of the Overview Pyramid contains a computed value for the measured LOC and NOM metric which shows us, that in the average each operation has 25 lines of code. This value can be described as very high, especially when you consider that most systems contain a variety of simple operation, like Getter and Setter, in addition to the main application logic.

Computed average values in the Overview Pyramid

To take reasonable conclusions from the computed values one important part is still missing, an adequate set of reference values. Without reference values, that say what values are low, average or high, it is not possible to classify these results. The current version of PHP_Depend supports a single set of reference values, this set was taken from [ML96].

Reference values

With these reference values PHP_Depend can classify the computed results. PHP_Depend uses this information for the generation of colored backgrounds, so that the color already supports the categorization.

The complete Overview Pyramid

The benefit of the Overview Pyramid

Of course, the final question is, which advantages offers the Overview Pyramid?

The Overview Pyramid provides a simple and size indipendent way to get a first impression of a software system, and this without an expensive source code analysis. Thus the Overview Pyramid is an effective tool for a first cost estimate for an unknown system. With the help of this tool and know-how, an experienced developer will quickly get a first impression and will know what can be expected from the analyzed application. And this knowledge could be a good help during the planning phase of a new project.

Bibliography

• Object-Oriented Metrics in Practice
  Using Software Metrics to Characterize, Evaluate, and Improve the Design of Object-Oriented Systems
  Michele Lanza, Radu Marinescu, 2006 © Springer-Verlag Berlin Heidelberg, ISBN 978-3-540-24429-5

If you like commit mails as I do, you can subscribe to the commit mailing list. Simply send an email to commits-join@pdepend.org or register thru the online interface.

If you have any PHP_Depend related questions, tips or suggestions, subscribe to the PHP_Depend user mailing list by mail users-join@pdepend.org or use the online interface.

Enjoy PHP_Depend!

  Manuel

Here a short follow up for the PHP_Depend release announcement, with hints on using PHP_Depend.

First I must explain that PHP_Depend is working package oriented. This means it heavily relies on @package and @subpackage annotations within the comment blocks. For these annotations PHP_Depend applies the following rules, these rules are borrowed from PEAR. Or was it PHPDocumentor?

1. function: The @package/@subpackage annotation in the file level comment is used for all functions declared within this file.
2. class/interface: The @package/@subpackage annotation within the class or interface comment is used for that type.
3. everything else: Everything that doesn't match on one of the previous rules is part of the +global Package.

With default settings PHP_Depend suppresses the +global Package, because it expects that this package contains classes from external libraries, like Zend Framework or eZComponents. If you use PHP_Depend for a project with less or no @package/@subpackage annotation, you should use the cli option --bad-documentation, which forces PHP_Depend to keep all classes, interfaces and functions within the +global package. This option was introduced with PHP_Depend - 0.8.0beta3.

The second important hint is related to exported charts and images. If your operation system, image viewer or browser supports SVG, you should use this format. The reason for this decision is really simple, SVG provides tooltips and so you get most informations from the generated graphics.

For the Overview-Pyramid this means, that you get a tooltip for the used acronyms.

PHP_Depend Overview-Pyramid with acronym tooltip

And within the JDepend-chart you get the package name as tooltip.

PHP_Depend JDepend-Chart with package tooltip

I hope this short introduction helps you while you are trying out PHP_Depend. If you are already using the metrics feature of PHPUnit, you should try out the new --phpunit-xml log option in the latest SVN-Revision.

This new release of PHP_Depend took some time to be finished. This is because the initial idea of a simple adaption of JDepend evolved (supported thru this blog-post by Sebastian), and so PHP_Depend has become a complete software metric application. Many new features and enhancements have found their way into this version. One of the key features is the pluggable architecture for custom Loggers and Metric-Analyzers. This opens the possibility to hook own Logger- and Analyzer-implementations into the execution chain of PHP_Depend. Beside these architectural changes this PHP_Depend version is shipped with a large set of implemented software metrics.

ClassLevel (Class)

• dit: Depth of Inheritance Tree
• impl: Number of implemented interfaces
• cis: Class Interface Size
• csz: Class SiZe
• vars: Number of defined class properties
• varsi: Number of own and inherited class properties
• varsnp: Number of public class properties
• wmc: Weighted Method per Class(Sum of method Cyclomatic Complexity)
• wmci: Weighted Method per Class + inherited WMC
• wmcnp: Weighted Method per Class for all public class methods

CodeRank (Class, Package)

An adaption of google's PageRank algorithm for classes and packages.

• cr: Forward CodeRank (based on incoming edges)
• rcr: Reverse CodeRank (based on outgoing edges)

Coupling (Project)

• calls: Number of called methods and functions
• fanout: Number of referenced types

Cyclomatic Complexity (Project, Method, Function)

• ccn: Cyclomatic Complexity
• ccn2: Extended Cyclomatic Complexity

Dependency (Package)

For details see the following entry.

• ca: Afferent coupling
• ce: Efferent coupling
• a: Abstraction
• i: Instability
• d: Distance

Hierarchy (Project)

• clsa: Number of abstract classes.
• clsc: Number of concrete classes.
• roots: Number of root classes within the analyzed system.
• leafs: Number of leaf classes.
• maxDIT: Max Depth of Inheritance Tree value

Inheritance (Project)

• andc: Average Number of Derived Classes.
• ahh: Average Hierarchy Height

NodeCount (Project, Package, Class, Interface)

• nop: Number Of Packages
• noc: Number Of Classes
• noi: Number Of Interfaces
• nom: Number Of Methods
• nof: Number Of Functions

NodeLOC (Project, Package, Class, Interface, Method, Function)

• loc: Lines Of Code
• cloc: Comment Lines Of Code
• ncloc: Non Comment Lines Of Code

Due to the fact that PHP is a loosely typed programming language, PHP_Depend can only approximate some values. But the measured results can be improved with a good and complete source code documentation, because PHP_Depend takes advantage of different doc comment annotations (@throws, @var, @return). So I suggest the use of a tool like PHP_CodeSniffer, to achieve better results.

Beside all these metrics, PHP_Depend also provides a new chart type, the "Overview Pyramid". The Overview Pyramid can be a handy tool to analyze legacy code. If you have read the book Object-Oriented Metrics in Practice you should know howto interpret the Overview Pyramid, all others have to wait for a detailed description.

PHP_Depend Overview Pyramid for PHP_Depend

This new version can be installed with the PEAR-Installer. Just discover the pear.xplib.de channel and install the latest PHP_Depend release. After PHP_Depend has been installed successfully, the new command line tool pdepend should exist.

 mapi@arwen ~ $ pear channel-discover pear.xplib.de
 mapi@arwen ~ $ pear install xplib/PHP_Depend-beta
 mapi@arwen ~ $ pdepend --help
 PHP_Depend 0.8.0beta1 by Manuel Pichler

 Usage: pdepend [options] [logger] <dir[,dir[,...]]>

   --jdepend-chart=<file>    Generates a diagram of the analyzed packages.
   --jdepend-xml=<file>      Generates the package dependency log.

   --overview-pyramid=<file> Generates a chart with an Overview Pyramid for the
                             analyzed project.

   --summary-xml=<file>      Generates a xml log with all metrics.

   --coderank-mode=<*[,...]> Used CodeRank strategies. Comma separated list of
                             'inheritance'(default), 'property' and 'method'.

   --suffix=<ext[,...]>      List of valid PHP file extensions.
   --ignore=<dir[,...]>      List of exclude directories.
   --exclude=<pkg[,...]>     List of exclude packages.

   --without-annotations     Do not parse doc comment annotations.

   --help                    Print this help text.
   --version                 Print the current PHP_Depend version.

There is also a Subversion repository at http://svn.pdepend.org/, where the latest development version can be found.

Please test this beta release and file bug-reports and feature-requests in the PHP_Depend bug tracker.

Except minor enhancements and bugfixes the latest phpUnderControl version comes with two new features.

Customizable tab-panel

This version allows you to define additional tabs in the main tab-panel. These can be used for further artifacts. Future phpUnderControl updates care about custom tabs and keep them in the new version.

Test execution time

This version has a new chart, which visualizes the trend of the unit test execution time.

Test execution time metric

To provide a flexible and extendable software, it is a good OO practice to reduce the dependencies between implementing classes. This could be achieved by developing against abstractions which means both, abstract classes and interfaces. By using abstractions instead of real implementation in the application you provide some sort of contract, that could be used by others to hook into the application with their own classes that fulfill the contract. Except the extensibility of an application a good abstraction reduces the risk of breaks in multiple subsystems when something was changed in a single package. But how to get rid of all these dependencies, doing this by hand will become an impossible job, at least for larger projects. At this point a tool should be used to assist the development process.

PHP_Depend is an adaption of the established Java development tool JDepend. This tool shows you the quality of your design in the terms of extensibility, reusability and maintainability. All these facts are influenced by the inter-package dependencies and the package abstraction that PHP_Depend visualizes in form of an abstract/instability chart and as a detailed XML report of all detected dependencies.

PHP_Depend calculates the following metrics by counting classes, interfaces and dependencies.

Ca - Afferent Couplings:

The number of other packages that depend upon classes within this package. This value is good indicator how changes to classes in this package would influence other parts of the software.

Ce - Efferent Couplings:

The number of other packages that classes from this package depend upon. This value indicates how sensitive this package is for changes to other packages.

I - Instability:

The ratio between efferent coupling (Ce) and the total package coupling (Ce + Ca) which is based on the following formula (Ce / (Ce + Ca)) and produces results in the range [0,1]. A value I=0 indicates a maximally stable package that depends upon nothing and I=1 indicates a total instable package that has no incoming dependencies but depends upon other packages.

A - Abstractness:

The ratio between abstract classes (ac) and the total of all classes (ac + cc) that is calculated by this formula (ac / (ac + cc)) that results in a value in the range [0,1]. A=0 means that all classes in this package are non-abstract while A=1 shows a package that only consists of abstract classes and interfaces.

With these values we can create a chart that visualizes the relationship between the instability (I) on the y-axis and the abstraction (A) on the x-axis.

Graphical view of PHP_Depend metrics

Because in a project not each package can achieve the optimal values of A = 1, I = 0 or A = 0, I = 1, we draw a diagonal between the two corners. This line is called the Main sequence and represents an average between abstraction (A) and instability (I). This means that packages near this line have a good mix between abstraction and instability. You can call these packages balanced. Because it is desirable for packages to be close to the Main sequence we have a fifth metric, the package distance (D) from this ideal.

D - Distance

The normalized distance has a value in the range [0,1] and is calculated by the formula ((A + I) - 1)

If you are interested in this subject and PHP_Depend you can check out the latest version, including the unit tests, from the subversion repository or simply install the PHP_Depend PEAR package. But be aware this software is at a very early stage.

mapi@arwen $ pear channel-discover pear.xplib.de
mapi@arwen $ pear install xplib/PHP_Depend-alpha

Now you can run PHP_Depend with the following command.

pdepend <source-dir> [<output-dir>]

If you are interested in the code coverage follow this link .

I will close this post with a cite of Robert Martin:

However, a metric is not a god; it is merely a measurement against an arbitrary standard.

The following sources were used for this post.

• OO Design Quality Metrics - An Analysis of Dependencies
• Managing Your Dependencies with JDepend
• JDepend