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>