A minimal Oracle Linux install contains a really small set of RPMs but typically not enough for a product to install on and a full/complete install contains way more packages than you need. While a full install is convenient, it also means that the likelihood of having to install an errata for a package is higher and as such the cost of patching and updating/maintaining systems increases.
In an effort to make it as easy as possible, we have created a number of pre-install RPM packages which don't really contain actual programs but they 're more or less dummy packages and a few configuration scripts. They are built around the concept that you have a minimal OL installation (configured to point to a yum repository) and all the RPMs/packages which the specific Oracle product requires to install cleanly and pass the pre-requisites will be dependencies for the pre-install script.
When you install the pre-install RPM, yum will calculate the dependencies, figure out which additional RPMs are needed beyond what's installed, download them and install them. The configuration scripts in the RPM will also set up a number of sysctl options, create the default user, etc. After installation of this pre-install RPM, you can confidently start the Oracle product installer.
We have released a pre-install RPM in the past for the Oracle Database (11g, 12c,..) and Oracle Enterprise Manager 12c agent. And we now also released a similar RPM for E-Business R12.