DBMS > Inroduction > What is Database Schema?
Data Abstruction: Designers to use complex data structures to represent data in the database for the efficient use of data. Since many database-system users are not computer trained, developers hide the storage complexity from users through several levels of abstraction using Schema.
Database Schema: A database schema is the skeleton structure that represents the logical view of the entire database. It includes descriptions of the database structure, how the data is organized, how the relations among them are associated, and the constraints that should hold on the database.
A database schema can be depicted by means of schema diagrams.
Schema Diagram: A diagrammatic display of (some aspects of) a database schema.
Database designers who design the schema to help programmers understand the database and make it useful.
A database schema can be divided broadly into two categories −
Physical Lavel (or internal View /Schema) − The physical level describes complex low-level data structures in detail. This type of schema pertains to the actual storage of data and its form of storage like files, indices, etc. It defines how the data will be stored in a secondary storage.
Logical level (or Conceptual View / Schema)- This level of abstraction describes what data are stored in the database, and what relationships exist among those data. Schema of database defines all tables, views, and integrity constraints. In this logical level thus describes the entire database in terms of a small number of relatively simple structures.
View level (or External View / Schema): It is the highest level of abstraction describes only part of the entire database. Even though the logical level uses simple structures, complexity may still remains because of the variety of information stored in a large database. Different users of a database system need different information thus needs different portion of a database. The view level of abstraction exists to simplify their interaction with the system. The system may provide many views for the same database.
What is the difference between Schema and Instance?
Databases change over time as information is inserted and deleted. The collection of information stored in the database at a particular moment is called an instance of the database.
The overall design of the database is called the database Schema. The database schema defines the tables in a database, the columns and their types, and also the primary key of a table.
Schema of a database keeps constant once created, while the actual data in the database tables may change all the time.
What is the difference between Table Schema and Tables?
- Schema is the structure and Table is set of data consisting rows and columns.
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