ODI, unlike OBIEE, stores the design and deployment data in database.
When you connect to Oracle Studio, it asks you to connect to a repository. You cannot use ODI studio without a database.
ODI organizes its data into two repositories, Master repository and Work repository.
Master repository stores the Topology information.
The actual mapping objects are stored in Work repository.
When you connect to a repository, you are connecting to a master repository, and optionally select a work repository to be connected at the same time.
Installing ODI studio takes less than 10 minutes. Installing OracleXE takes less than 30 min. Within an hour, you should be able to get ready for your experiment of ODI.