Three Views of a Database, Part 2

14.07.2014 Fabian Rendon
Internal Data Level – The internal schema is also referred to as the physical schema. It elaborates the details of the way the data gets stored, providing indices, files and other information. It will also describe the the types of files and layouts such as flat, b-tree or hash. The earlier systems were based on this level. They were mainly dealing with details like reducing physical distance between related data or organization of data structures in the file.

In this schema, the routines get hardcoded for dealing with physical representation. It is difficult to make any alterations to the data structures. The complexity of the application code increases because it has to deal with details. It is quite difficult with this schema to implement any new features rapidly.

The three view levels in database systems have two types of mapping. Mapping is the process for converting a request and the result between the view levels. Even the description of mapping gets stored in the data dictionary. It is the database management system that conducts mapping between the 3 types of levels. The two types of mapping are external-conceptual and conceptual-internal mapping.

External-Conceptual Mapping – External-conceptual mapping will define the correspondence between a specific external view and conceptual view. It will tell the management system the objects at the conceptual level that correspond to the requested objects at a specific user’s external view. When any changes are made to external or conceptual view, it is important to change mapping accordingly.

Conceptual-Internal Mapping – This mapping defines the translation between conceptual and internal view. It defines the way conceptual records will be stored in and retrieved from the storage. This type of mapping will tell the management system about the physical representation of the conceptual records.

If there are any changes in the stored database’ structure, it is important to change the mapping accordingly. The database administrator is responsible for managing any such changes.

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