Kiruba,
I think your question was more around 'generic' application oracle DBA. An application DBA is a DBA who supports DBA activities in the context of applications running against the Database. An application DBA analysis the Application logical datamodel and converts it into a physical data model, recommends and implements performance enhancements in the database like indexing, database physical characteristics like PCTFREE, PCTUSED coming more from the application requirements. A systems/maintenace/administrative DBA is one who works outside the application(s) context. Hope that explains.