Internal level - the internal level has an internal schema which describe the physical storage structures of the database the internal schema. user a physical data models and describe the complete details of the data storage and access for for the database.
Conceptual level - the conceptual level has a conceptual schema which describes The structures of the whole database for a community of users the conceptual schema hide the details of physical storage structures and concentrates on describing describing entities. data types relationships user operations and constraint high levels data models in import implementations data models can be used at this level.
External or view level - the external of view level include in number of external schemes of or user views each external schma describes the part of the database that a particular user group in interested in and hides the rest of a database from that user group high level data model of an implementations data models can be used at the sea level.
The conceptual internal mapping it's defines the correspondence-between the conceptual of view and the stored data base. it specify how conceptual records and fields are represented at the internal level. If the structures for the stored database is changed if a change is made to the storage structures or in database , then the conceptual internal mapping must be changed accordingly so that the conceptual schema can remains invariant.
the external perceptual mapping it's defence the correspondence between if particular Re external view and the conceptual view any number of external views can exist at the same time any number of user can share a given external view.