比如：
tenace作为pom项目已经发布至repo，如果没有指定relativapath。则mvn -X -e clean package可以看到如下警告信息：
[WARNING][WARNING] Some problems were encountered while building the effective model for
com.spider:engine:jar:2.6.0-SNAPSHOT
[WARNING] ‘parent.relativePath‘ points at com.spider:spiderinstead of c
om.tenace:tenace, please verify your project structure @ line 4, column 10
[WARNING][WARNING] It is highly recommended to fix these problems because they threaten t
he stability of your build.
[WARNING][WARNING] For this reason, future Maven versions might no longer support buildin
g such malformed projects.
解决办法则是加上。
说明见链接：http://maven.apache.org/ref/3.0.3/maven-model/maven.html#class_parent
说明如下：
The relative path of the parent pom.xml file within the check out. If not specified, it defaults to ../pom.xml. Maven looks for the parent POM first in this location on the filesystem, then the local repository, and lastly in the remote repo. relativePath allows you to select a different location, for example when your structure is flat, or deeper without an intermediate parent POM. However, the group ID, artifact ID and version are still required, and must match the file in the location given or it will revert to the repository for the POM. This feature is only for enhancing the development in a local checkout of that project. Set the value to an empty string in case you want to disable the feature and always resolve the parent POM from the repositories.
Default value is: ../pom.xml.
