What is a Schema?
A database schema is the skeleton structure that represents the logical view of the entire database. It defines how the data is organized and how the relations among them are associated. It formulates all the constraints that are to be applied on the data. A database schema defines its entities and the relationship among them. It contains a descriptive detail of the database, which can be depicted by means of schema diagrams. It’s the database designers who design the schema to help programmers understand the database and make it useful.
There are three types of schemas: physical schema, logical schema, and view schema. The physical schema describes the way data is stored in blocks of memory, while the view schema explains the end-user’s interactions with the database. The logical schema, on the other hand, describes the design of the database on a logical level. Programmers and database administrators work at this level.
We can display a database schema in the form of a diagram referred to as a schema diagram. This diagram indicates what data contains in a table, what variables are, and how they are associated with each other. Note that the schema diagram doesn’t show every aspect of the database, such as database instances, type of the attributes, etc.
We can specify the schema using the DDL (Data Definition Language) statements. The DDL statement sets the table name, the attributes and their types, constraints, and its relation with other tables in a database. We can also use this statement when we want to modify the schema.
What you need to know about schema
- Schema refers to the overall description of any given database.
- Schema remains the same for the entire database.
- It doesn’t change frequently.
- It tells about how the data would be stored in a database.
- Schema is used for defining the basic structure of any given database. It defines how the available needs to get stored.
- Schema is of three types: Physical schema, logical schema and view schema.
- A schema contains schema objects like table, foreign key, primary key, views, columns, data types, stored procedure, etc.
- A database schema is the skeleton structure of the database. It represents the logical view of the entire database.
What is Instance?
A database instance is a state of operational database with data at any given time. It contains a snapshot of the database. Database instances tend to change with time. A DBMS ensures that its every instance (state) is in a valid state, by diligently following all the validations, constraints, and conditions that the database designers have imposed.
In other words, data stored in database at a particular moment of time is called instance of database. Database schema defines the variable declarations in tables that belong to a particular database; the value of these variables at a moment of time is called the instance of that database.
What you need to know about Instance
- Instance refers to the collection of information that is stored in the database at a specific time.
- Data in the instances can be changed. This can be done using addition, deletion, and updating.
- The instance changes frequently.
- It tells us the set of Information that is stored at a particular time.
- Instance is used for referring to a set of information at any given instance/ time.
The data stored in database at a particular moment of time is called instance of database. Database schema defines the variable declarations in tables that belong to a particular database; the value of these variables at a moment of time is called the instance of that database