Storing data collection in a database at a particular moment in time is called an instance. The word instance is used to describe the entire database environment that includes DBMS software, data in tabular form, and other logical functionality.
We can also define it as where data is stored in a manageable manner. The instances in the database vary according to the situation.
Schema means structure. A schema is an organization or structure for a database that describes the logical view of the complete database. It shows how data are organized and managed in the database. It also reflects the relationship between each data to other data present in that database. Database designers design schemas so that programmers can easily understand the database structure and make the database usable. Generally, the schema is stored in the database.
The objective of database schema is to recognize different tuples and fields of each table easily and the schema describes the relationship between these tables. This helps to identify constraints in the system.
The subschema is a subset of the schema and the subschema has the same property as the schema.
The schema can be divided into two parts
- Physical schema
- Logical schema
a) Physical schema – Physical schema defines how data is represented in DBMS and how data is stored in it.
b) Logical schema – This schema defines all the logical constraints applied in storing data. A logical schema defines the conceptual model of data in the database.