The following are the three scenarios in which an upgrade is performed:
Side-by-side Upgrade: The source server and the target server are installed on the same machine , but under different install locations. You can choose to perform this type of upgrade if you wish to have the configuration corresponding to these installations on the same machine in different locations.
In-place Upgrade: The target server is installed in the same installation location as the source server. You can choose to perform this type of upgrade if you wish to install the configuration (that is, the domains ) in the same location as before. In this scenario, you install the binaries in the same location as the existing binaries using the installer.
Inline Upgrade: You can use the start-domain command to upgrade domains of Application Server 8.x or 9.0 to Application Server 9.1. This type of upgrade works only if you are performing an in-place upgrade of binaries.