Three-schema database systems architectures group database systems into three levels
Response 1
Discuss/define the data independence concept provided by the three-schema database systems architecture. What are the two types of data independence? Which type is much harder to achieve and why?
Three-schema database systems architectures group database systems into three levels: externally or from the point of view of the user, conceptually or logically from the point of view of the database, and physically or internally from the point of view of the database. A key concept of this architecture is data independence, which means that modifications can be made to one level of the database system without having an impact on the other levels.
Physical data independence and logical data independence are two types of data independence. In the context of physical data independence, it means that the database’s conceptual or external view can remain the same if the physical storage devices or structures change. The concept of logical data independence implies that the external views or the physical storage structures can be changed without affecting the conceptual schema.
Due to the need to change the actual storage structures of the data, physical data independence is more difficult than logical data independence, which can adversely affect the performance and functionality of the database system. The conceptual schema, which represents data at a high level and is independent of physical storage structures, can achieve logical data independence relatively easily.
ANSI/SPARC Study Group introduced the concept of data independence and three-scheme database systems architecture in the 1970s. Several database systems have been designed and implemented using this architecture.
Response 2
The ability to make changes to the database’s schema at any level without impacting the schema at higher levels is known as data freedom. Changing data at one level should only affect data at one level. No adjustments need to be made to the data access or storage mechanisms at the subsequent level. “Data abstraction” describes how a DBMS separates itself from its data. Database management systems (DBMS) support both physical and logical data freedom.
Types
1. Logical data independence
In order to update the conceptual plan without impacting other schemas or applications, we require logical data independence. Modifications to the overall plan are necessary for either growing or shrinking the database. The third case, when the residual data is used by external schemas, should be fine.
2. Physical data independence
Independence modifies the conceptual schema of biological data without affecting the internal schema. As a result, it is unnecessary to update any external schemas. Due to the relocation of some files, it may be necessary to adjust the underlying data structure.
Achieving logical data independence is more challenging than achieving physical data independence because application programs depend heavily on logical arrangement of the information they access.
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