Three Schema Architecture
The three-schema architecture is commonly known as the three-tier architecture or ANSI/SPARC architecture. These terms and framework are for describing a particular database system structure. The physical database and the user applications are kept separate using this three-tier architecture. This type of architecture has three, which are what keeps the user and the database separate.
The framework of this type of architecture includes an external schema, a conceptual level, an internal schema, and then the database itself. The various levels of the database are mapped, which leads to the transformation of response and request in the database. Smaller DBMS are challenging to map since they are more time-consuming. In the external/conceptual mapping, the transformation of the request to the conceptual level from the external level is necessary. In the conceptual/ internal mapping, the request received from the conceptual level is transformed to the internal level by the DBMS.
1. Internal Level:
- The internal level consists of an internal schema which is used to describe the physical structure of the database in which the data is stored.
- This schema is often called as the physical schema.
- The internal level uses the physical data model. This data model describes the method by which the data should be stored in a block.
- Complex low-level data structures are described in detail in this schema.
2. Conceptual Level:
- The conceptual schema elaborates the database and its data along with the design at a conceptual level.
- The conceptual level is often known as the logical level.
- Conceptual level is used for describing the entire database with its structure.
- This level also describes where the data which is stored in the entire database and the relation about the data as well.
- The data structure’s implementation and other internal details are hidden at the conceptual level.
- Administrators and programmers work on the database at the conceptual level.
3. External Level:
- A database contains various schemas at this level, and these schemas may also be called as subschemas. These are used to describe the possible different views in the database.
- View schema is another name for the external schema.
- External level describes the user and his interaction with the data in the database.