聚合：一条命令构建多个模块。

父子关系，account-aggregator与account-email、account-persist为父子关系

<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion >
	<groupId>com.juvenxu.mvnbook.account</groupId>
	<artifactId>account-aggregator</artifactId >
	<version>1.0.0-SNAPSHОT</version>
	<packaging>pom</packaging>
	<name>Account Aggregator</name >
	<modules>
		<module>account-email</module >
		<module>account-persist</module >
	</modules>
</project>

平行目录

	<modules>
		<module>../account-email</module >
		<module>../account-persist</module >
	</modules>