A common confusion I usually see among beginners is differentiating between a Database, a Database instance and Database schema. Let’s get that cleared, shall we?

What is a Database?

Databases are computer structures that save, organize, protect, and deliver data. Any system that manages databases is called a database management system, or DBM. The database table is where all the data in a database is stored using a model of vertical columns (identifiable by name) and horizontal rows, the cell being the unit where a row and column intersect. A table has a specified number of columns but can have any number of rows.

What is a DB Schema?

Design of a database is called the schema. Schema is of three types: Physical schema, logical schema and view schema.

Physical Schema: The design of a database at physical level, how the data stored in blocks of storage is described at this level.

Logical Schema: Design of database at logical level. Programmers and database administrators work at this level. It is a model that exists on a white board or in a diagramming tool. It is like the architect’s drawings of your database.

View Schema: Design of database at view level is called. This generally describes end user interaction with database systems.

What is a DB instance?

While the database itself includes all the application data and metadata stored in physical files on a server, an instance is a combination of the software and memory used to access that data. An instance can have multiple databases.

A Tasty Analogy

Consider a multi-layer tiffin box as an analogy.

The individual boxes are the tables storing the data which is the food. The stack of the tiffin boxes i.e. a collection of tables forms the database. The tiffin stack, the lids and the supporting rack combined are stored in the tiffin bag which is the Database instance in this analogy. Since the stack of tiffin boxes in the picture is a representation of the DB, the picture itself would be the schema as it tells us the number of tables, the design etc.