Three-Level Schema Architecture Quiz & Flashcards

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Questions and Answers

What is the name of the three-level architecture proposed in 1971 by a Special interest group?

ANSI-SPARC architecture

What is the aim of presenting the ANSI-SPARC architecture?

To provide a framework for describing general database concepts and explaining the structure of specific database systems.

What are the three different levels at which data in a database is described?

External schema, conceptual schema, physical or internal schema.

Which level in the three-level schema architecture is nearest to the storage level?

Physical or internal schema Signup and view all the answers

What is the purpose of the conceptual schema in the three-level schema architecture?

It represents the logical structure of the entire database. Signup and view all the answers

What is the role of the external schema in the three-level schema architecture?

It represents the user views or user interface to the database. Signup and view all the answers

What is the purpose of the external level in a database system?

The external level is concerned with the way the data is seen by individual users, either application programmers or end users. It describes a portion of the database that is of concern to the specific user and includes only those entities, attributes and relationships that are of interest to the user. Signup and view all the answers

How does the conceptual level differ from the external level in a database system?

The conceptual level represents the community view of the database as seen by the database administrator. It defines the logical structure of all data in the database, including the structure and constraints for the whole database. In contrast, the external level describes a portion of the database that is of concern to a specific user. Signup and view all the answers

What is the purpose of data independence in a database system?

Data independence is achieved by defining the conceptual schema using a Data Definition Language (DDL) that does not involve any consideration of the physical representation or access techniques. This allows changes to the physical implementation of the database without affecting the conceptual or external schemas. Signup and view all the answers

How can users access the external schema in a database system?

Users can access the external schema using a tool or language specific to their needs. Application programmers can use a conventional programming language (e.g., C++, Java, 4GL), while end users would use a query language or some special-purpose language (SQL or query-by-form). Signup and view all the answers

What is the purpose of the conceptual schema in a database system?

The conceptual schema is used to describe what data is stored in the database and the relationships among the data. It defines the logical structure of all data in the database, including the structure and constraints for the whole database. Signup and view all the answers

How can the external view of the database differ from the actual stored data?

The external view could possibly represent records in a different model than the stored level. For example, one view could show the price of an item in American Dollars while another view in German Francs, even though the actual value of the item is stored in Euros. The item price is stored in one currency and is converted (derived) into different currencies when it is needed (whenever the user views it). Signup and view all the answers

Study Notes

ANSI-SPARC Architecture

Named ANSI/SPARC architecture, proposed by a special interest group in 1971.
Designed to standardize the way databases are conceived and managed.

Aim of ANSI-SPARC Architecture

Aims to provide a framework for database systems that separates user views from storage details.

Three Levels of Data Description

External Level: Individual user views of the database, tailored to their needs.
Conceptual Level: Overall logical structure of the entire database, including all entities and relationships.
Internal Level: Physical storage structure of the database, detailing how data is stored.

Nearest Level to Storage

The internal level is the closest to the storage level, representing how data is physically stored on devices.

Purpose of Conceptual Schema

Acts as a unified view of the entire database, ensuring that all data relationships and constraints are logically represented.

Role of External Schema

Defines user-specific views, allowing different users to see the same data in different formats or presentations.

Purpose of External Level

Designed to provide various user interfaces, offering individualized views without impacting the underlying structure of the database.

Conceptual Level vs. External Level

The conceptual level represents the complete logical structure of data, while the external level provides tailored views for individual users.

Purpose of Data Independence

Allows changes to the database structure without affecting the user applications or requiring changes to external schemas.

Accessing the External Schema

Users can access the external schema through interfaces or applications customized to retrieve and manipulate data according to their specific needs.

Conceptual Schema Purpose in Database

Serves as the foundation for data integrity and consistency, encompassing all entities and their interrelationships.

Differences in External View vs. Stored Data

The external view can vary significantly from the actual stored data, allowing for simplified or transformed representations that meet user requirements, avoiding complexity in the underlying data structure.

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Description

Explore the features and advantages associated with having a DBMS with different levels of abstractions. Learn how multiple user views, data and program independence, and the use of a catalog for storing database descriptions (schema) are achieved through the three-level schema architecture.