Describe the three-schema architecture. Why do we need mappings among schema levels? How do different schema definition language
s support this architecture?
1 answer:
Answer:
Three Scheme architecture contains internal level, conceptual level, and external level.
In the internal level physical structure of the database described. The internal Schema is also known as physical Schema, as it is used to define the data that stored in a block. Internal Schema describes a sophisticated level of data structure in detail.
The conceptual level design of the database has described, and it is known as a logical level. The conceptual level describes the whole structure of the database. It describes the relationships among the data. Implementation of data are hidden in a theoretical level
On the external level, databases contain schemas that represent a different view of the database. Each describes the database that the user interested in and hides the remaining database. The external database is also known as view schema.
Explanation:
The mappings between schema levels happen due to visualization and schema matching. DBMS has three schema level.
In the attached diagram
It shows the DBMS architecture.
Mapping is a way to transfer and respond to the request between the various database architecture.
Mapping takes more time to transfer data in small DBMS.
External / Conceptual mapping transforms the data from the outer level to the conceptual schema.
In Conceptual / Internal mapping, response transforms from conceptual to internal level.
Document Schema Definition Language (DSDL) is a framework in which multiple validations can be applied to achieve a complete validation result. In this way, schema definition language support this architecture.
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