From Wikipedia..."IBM DB2 is a family of database server products developed by IBM. These products all support the relational model, but in recent years some products have been extended to support object-relational features and non-relational structures like JSON and XML."

From Ross...DB2 is the naitive database used on the IBM series of midrange systems including the iSeries. I develop in DB2 when developing applications on the iSeries. DB2 can be managed from iSeries command lines or the System i Navigator product. DB2 on the iSeries is a modern, fast and easy to use RDMS that is closely tied to the iSeries operating system and is managed directly by the operating system. DB2 on the iSeries does not generally require intervention of a DBA.