The main difference between schema and instance is that schema is a structural view of the database, while the instance is the data stored in a database at a particular moment of time.
The database is a collection of organized data. DBMS is a software program that helps to store and manage data in multiple databases. Furthermore, RDBMS is a special type of DBMS. Overall, schema and instance are two terms in databases and DBMS.
Key Areas Covered
DBMS, DDL, Instance, Logical Schema, Physical Schema, Schema, View Schema
What is Schema
Schema is a structural view of a database. Moreover, a schema diagram refers to representing a database as a diagram. It represents the relationship between the tables. However, it does not show the data present in the tables.
There are three types of schemas: physical schema, logical schema, and view schema. The physical schema describes the way of storing data in blocks of storage, while view schema explains the end-user interactions with the database. Logical schema, on the other hand, describes the design of the database at a logical level. Programmers and database administrators work at this level.
Moreover, Data Definition Language (DDL) statements help to denote the schema of a database. The schema represents the name of the table, name of attributes and their types; constraints of the tables are related to the schema. Therefore, if users want to modify the schema, they can write DDL statements.
What is Instance
An instance of the database is the data in the database at a specific moment of time. The database schema defines the variable declarations in tables and the values of these variables at a specific time are called the instance of the database.
For example, assume that there are 100 records in the employee table of the database. So, the instance of the database has 100 records. After one month, there are 120 records in the employee table of the database. So, the instance of the database has 120 records. Likewise, instance refers to the data stored in a database at a particular moment. Furthermore, it can change depending on the tasks such as addition, deletion, etc.
Difference Between Schema and Instance
Schema is a visual representation of a database which is a set of rules that govern a database. In contrast, the instance is the data stored in a database at a particular time.
Schema is a formal description of the structure of the database, while the instance is the set of information stored in a database at a particular time.
Furthermore, the schema does not frequently change, whereas instance changes frequently.
Schema and instance are two terms related to databases and DBMS. In brief, the main difference between schema and instance is that a schema is a structural view of the database, while the instance is the data stored in a database at a particular moment of time.
1.Singh, Chaitanya. “Instance and Schema in DBMS.” Beginnersbook.com, 14 Nov. 2018, Available here.
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