POM stands for Project Object Model. It’sfundamental unit of work in Maven. It’san XML file that resides in the base directory of the project as pom.xml.
The POM contains information about the project and various configuration detail used by Maven to build the project(s).
POM also contains the goals and plugins. While executing a task or goal, Maven looks for the POM in the present directory. It reads the POM, gets the needed configuration information, and then executes the goal. Some of the configuration that can be specified in the POM are subsequent −
• project dependencies
• plugins
• goals
• build profiles
• project version
• developers
• mailing list
Before creating a POM, we should first decide the project group (groupId), its name (artifactId) and its version as these attributes help in uniquely identifying the project in repository.

POM Example

<groupId>com.companyname.project-group</groupId>
<artifactId>project</artifactId>
<version>1.0</version>
</project>
It should be noted that there should be a single POM file for each project.
• All POM files require the project element and three mandatory fields: groupId, artifactId, version.
• Projects notation in repository is groupId:artifactId:version.
• Minimal requirements for a POM −

Sr.No.	Node & Description
1	Project root This is project root tag. You need to specify the basic schema settings such as apache schema and w3.org specification.
2	Model version Model version should be 4.0.0.
3	groupId This is an Id of project’s group. This is generally unique amongst an organization or a project. For example, a banking group com.company.bank has all bank related projects.
4	artifactId This is an Id of the project. This is generally name of the project. For example, consumer-banking. Along with the groupId, the artifactId defines the artifact’s location within the repository.
5	version This is the version of the project. Along with the groupId, It’sused within an artifact’s repository to separate versions from each other. For example − com.company.bank:consumer-banking:1.0 com.company.bank:consumer-banking:1.1.

Super POM

The Super POM is Maven’s default POM. All POMs inherit from a parent or default (despite explicitly defined or not). This base POM is known as the Super POM, and contains values inherited by default.
Maven use the effective POM (configuration from super pom plus project configuration) to execute relevant goal. It helps developers to specify minimum configuration detail in his/her pom.xml. Although configurations can be overridden easily.
An easy way to look at the default configurations of the super POM is by running the subsequent command: mvn help:effective-pom
Create a pom.xml in any directory on your computer.Use the content of above mentioned example pom.
In example below, We’ve created a pom.xml in C:\MVN\project folder.
Now open command console, go the folder containing pom.xml and execute the subsequent mvn command.
C:\MVN\project>mvn help:effective-pom
Maven will start processing and display the effective-pom.
[INFO] Scanning for projects…
[INFO] Searching repository for plugin with prefix: ‘help’.
[INFO] ————————————————————————
[INFO] Building Unnamed – com.companyname.project-group:project-name:jar:1.0
[INFO] task-segment: [help:effective-pom] (aggregator-style)
[INFO] ————————————————————————
[INFO] [help:effective-pom {execution: default-cli}]
[INFO]

…..

[INFO] ————————————————————————
[INFO] BUILD SUCCESSFUL
[INFO] ————————————————————————
[INFO] Total time: < 1 second
[INFO] Finished at: Thu Jul 05 11:41:51 IST 2012
[INFO] Final Memory: 6M/15M
[INFO] ————————————————————————
Effective POM displayed as result in console, after inheritance, interpolation, and profiles are applied.
<?xml version=”1.0″ encoding=”UTF-8″?>
<!– ============================================== –>
<!– –>
<!– Generated by Maven Help Plugin on 2015-04-09T11:41:51 –>
<!– See: http://maven.apache.org/plugins/maven-help-plugin/ –>
<!– –>
<!– ==============================================–>

<!– ==============================================–>
<!– –>
<!– Effective POM for project –>
<!– ‘com.companyname.project-group:project-name:jar:1.0’ –>
<!– –>
<!– ============================================== –>

<project xmlns = “http://maven.apache.org/POM/4.0.0” xmlns:xsi = “http://www.w3.org/

2001/XMLSchema-instance” xsi:schemaLocation = “http://maven.apache.org/POM/4.0.0

http://maven.apache.org/xsd/maven-4.0.0.xsd”>
<modelVersion>4.0.0</modelVersion>
<groupId>com.companyname.project-group</groupId>
<artifactId>project</artifactId>
<version>1.0</version>
<build>
<sourceDirectory>C:\MVN\project\src\main\java</sourceDirectory>
<scriptSourceDirectory>src/main/scripts</scriptSourceDirectory>

<testSourceDirectory>C:\MVN\project\src\test\java</testSourceDirectory>
<outputDirectory>C:\MVN\project\target\classes</outputDirectory>
<testOutputDirectory>C:\MVN\project\target\test-classes</testOutputDirectory>
<resources>
<resource>
<mergeId>resource-0</mergeId>
<directory>C:\MVN\project\src\main\resources</directory>
</resource>
</resources>
<testResources>
<testResource>
<mergeId>resource-1</mergeId>
<directory>C:\MVN\project\src\test\resources</directory>
</testResource>
</testResources>
<directory>C:\MVN\project\target</directory>
<finalName>project-1.0</finalName>

<pluginManagement>
<plugins>
<plugin>
<artifactId>maven-antrun-plugin</artifactId>
<version>1.3</version>
</plugin>
<plugin>
<artifactId>maven-assembly-plugin< /artifactId>
<version>2.2-beta-2</version>
</plugin>
<plugin>
<artifactId>maven-clean-plugin< /artifactId>
<version>2.2</version>
</plugin>

<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>2.0.2</version>
</plugin>
<plugin>
<artifactId>maven-dependency-plugin</artifactId>
<version>2.0</version>
</plugin>
<plugin>
<artifactId>maven-deploy-plugin</artifactId>
<version>2.4</version>
</plugin>

<plugin>
<artifactId>maven-ear-plugin</artifactId>
<version>2.3.1</version>
</plugin>
<plugin>
<artifactId>maven-ejb-plugin</artifactId>
<version>2.1</version>
</plugin>
<plugin>
<artifactId>maven-install-plugin</artifactId>
<version>2.2</version>
</plugin>

<plugin>
<artifactId>maven-jar-plugin</artifactId>
<version>2.2</version>
</plugin>
<plugin>
<artifactId>maven-javadoc-plugin</artifactId>
<version>2.5</version>
</plugin>
<plugin>
<artifactId>maven-plugin-plugin</artifactId>
<version>2.4.3</version>
</plugin>

<plugin>
<artifactId>maven-rar-plugin</artifactId>
<version>2.2</version>
</plugin>
<plugin>
<artifactId>maven-release-plugin</artifactId>
<version>2.0-beta-8</version>
</plugin>
<plugin>
<artifactId>maven-resources-plugin</artifactId>
<version>2.3</version>
</plugin>

<plugin>
<artifactId>maven-site-plugin</artifactId>
<version>2.0-beta-7</version>
</plugin>
<plugin>
<artifactId>maven-source-plugin</artifactId>
<version>2.0.4</version>
</plugin>
<plugin>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.4.3</version>
</plugin>
<plugin>
<artifactId>maven-war-plugin</artifactId>
<version>2.1-alpha-2</version>
</plugin>
</plugins>
</pluginManagement>

<plugins>
<plugin>
<artifactId>maven-help-plugin</artifactId>
<version>2.1.1</version>
</plugin>
</plugins>
</build>

<repositories>
<repository>
<snapshots>
<enabled>false</enabled>
</snapshots>
<id>central</id>
<name>Maven Repository Switchboard</name>
<url>http://repo1.maven.org/maven2</url>
</repository>
</repositories>
<pluginRepositories>
<pluginRepository>
<releases>
<updatePolicy>never</updatePolicy>
</releases>
<snapshots>
<enabled>false</enabled>
</snapshots>
<id>central</id>
<name>Maven Plugin Repository</name>
<url>http://repo1.maven.org/maven2</url>
</pluginRepository>
</pluginRepositories>
<reporting>
<outputDirectory>C:\MVN\project\target/site</outputDirectory>
</reporting>
</project>
In above pom.xml, you can see the default project source folders structure, output directory, plug-ins required, repositories, reporting directory, which Maven will be using while executing the desired goals.
Maven pom.xml is also not required to be written manually. Maven provides numerous archetype plugins to create projects, which in order, create the project structure and pom.xml
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