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Authors:
Elmasri Navathe
Chapter:
Relational Data Model And Relational Database Constraints
Exercise:
Review Questions
Question:1 | ISBN:9780133970777 | Edition: 7

Question

Define the following terms: data model, database schema, database state, internal schema, conceptual schema, external schema, data independence, DDL, DML, SDL, VDL, query language, host language, data sublanguage, database utility, catalog, client/server architecture, three-tier architecture, and n-tier architecture.

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Answer

Data Model:

  • A data model is a conceptual representation of the data structures, relationships, constraints, and operations that can be performed on the data within a database system. It provides a way to organize and structure data in a meaningful way.

Database Schema:

  • A database schema is a description or blueprint of the structure, organization, and relationships of a database. It defines the tables, attributes, data types, constraints, and other properties of the data stored in the database.

Database State:

  • The database state refers to the current data stored in the database at a specific point in time. It represents the values and relationships of the data as it exists in the database at a particular moment.

Internal Schema:

  • The internal schema, also known as the physical schema, is the low-level representation of the database that describes how the data is stored and accessed physically on the storage media. It defines the storage structures, file organizations, indexing techniques, and other implementation details.

Conceptual Schema:

  • The conceptual schema, also known as the logical schema, is an abstract representation of the entire database system. It describes the overall structure of the database, including the entities, attributes, relationships, and constraints, without specifying the physical implementation details.

External Schema:

  • An external schema, also known as a view or user schema, represents a specific user's or application's view of the database. It defines the subset of the conceptual schema that is relevant and accessible to a particular user or application. It provides a customized and simplified representation of the database for specific user requirements.

Data Independence:

  • Data independence refers to the ability to modify the database schema or internal organization without affecting the external schemas or application programs that use the database. It allows changes to be made at one level without requiring changes at other levels.

DDL (Data Definition Language):

  • DDL is a language used to define and manage the database schema. It includes commands like CREATE, ALTER, and DROP to create, modify, and delete database objects such as tables, views, indexes, and constraints.

DML (Data Manipulation Language):

  • DML is a language used to manipulate and retrieve data within the database. It includes commands like SELECT, INSERT, UPDATE, and DELETE to insert, modify, retrieve, and delete data stored in the database tables.

SDL (Storage Definition Language):

  • SDL is a language used to define and manage the internal schema or physical organization of the database. It includes commands for specifying storage structures, file organizations, indexing techniques, and other implementation-specific details.

VDL (View Definition Language):

  • VDL is a language used to define and manage the external schema or views in the database. It allows users to define their customized views and specify the subset of data they are interested in.

Query Language:

  • A query language is a language used to communicate with a database and retrieve specific information or perform operations on the database. SQL (Structured Query Language) is the most commonly used query language for relational databases.

Host Language:

  • A host language is a programming language in which database commands or queries can be embedded. It allows for the integration of database operations within a general-purpose programming language.

Data Sublanguage:

  • A data sublanguage is a subset of a complete query language that deals specifically with database-related operations. For example, SQL is a data sublanguage that focuses on querying and manipulating data in relational databases.

Database Utility:

  • A database utility is a software tool or program that provides additional functionalities for managing and maintaining databases. It includes backup and recovery utilities, database optimization tools, data migration tools, and other tools that assist in database administration tasks.

Catalog:

  • The catalog, also known as the system catalog or data dictionary, is a database component that stores metadata or information about the database objects such as tables, views, indexes, and constraints. It provides a centralized repository for storing and accessing information about the database schema and data.

Client/Server Architecture:

  • Client/server architecture is a distributed computing model where the database system is divided into two components: the client, which requests database operations, and the server, which handles the processing and storage of data. The client sends requests to the server, which processes the requests and sends back the results.

Three-Tier Architecture:

  • Three-tier architecture is a client/server architecture that divides the database system into three layers: the presentation layer (client), the application logic layer (middle-tier), and the data storage layer (database server). It provides a modular and scalable approach to building database applications.

N-Tier Architecture:

  • N-tier architecture is an extension of the three-tier architecture, where the database system is divided into multiple layers or tiers, each responsible for a specific function or task. It allows for more flexibility, scalability, and modularity in designing complex database systems.
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