Three Schema Architecture

1. Internal Scheme - Internal Level
   1. Describes physical storage structure
   2. Uses a physical data model
2. Conceptual Schema - Conceptual Level
   1. Describes structure for a community of users
   2. Uses conceptual data model or implementation data model
3. External Schema - External Level
   1. Describes various user views
   2. Usually uses the same model as conceptual schema

• Mapping among schemas are needed to process requests.