Defining a parent module
In most of the multi-module Maven projects, there are many things that are shared across multiple modules. Dependency versions, plugin versions, properties, and repositories are only some of them. It is a common (and a best) practice to create a separate module called parent and define everything in common in its POM file. The packaging type of this POM file is pom. The artifact generated by the pom packaging type is itself a POM file.
The following are few examples of Maven parent modules:
Apache Axis2 project: http://svn.apache.org/repos/asf/axis/axis2/java/core/trunk/modules/parent/
WSO2 Carbon project: https://svn.wso2.org/repos/wso2/carbon/platform/trunk/parent/
Not all the projects follow this approach. Some just keep the parent POM file under the root directory (not under the parent module). The following are a couple of examples:
Apache Synapse project: http://svn.apache.org/repos/asf/synapse/trunk/java/pom.xml
Apache HBase project: http://svn.apache.org...
