What is schema in database

Database schema design refers to the practices and strategies for constructing a database schema. The schema is an abstract structure or outline that represents the logical view of the database as a whole. By defining categories of data and relationships between those categories, database schema design makes data much easier to retrieve, consume, manipulate, and interpret. Database schema design organizes the data into separate entities, determines how to create relationships between organized entities, and how to apply the constraints on the data.

Designers create database schemas to give other database users, such as programmers and analysts, a logical understanding of the data.

Integrate Your Data Today! Try Xplenty free for 7 days. No credit card required. Get Started. Databases that are inefficiently organized suck up tons of energy and resources, tend to be confusing, and are hard to maintain and administer. For example, the same data might be duplicated in multiple locations—or even worse, might be inconsistent between these locations. It describes both the organization of data and the relationships between tables in a given database. Developers plan a database schema in advance so they know what components are necessary and how they will connect to each other.

In this guide, we will learn what a database schema is and why they are used. We will go through a few common examples so you can learn how to configure a database schema on your own. Database Design Fundamentals for Software Engineers. When it comes to choosing your database, one of the things you have to think about is the shape of your data, what model it will follow, and how the relationships formed will help us as we develop a schema.

A database schema is a blueprint or architecture of how our data will look. An entry in our database will be an instance of the database schema. It will contain all of the properties described in the schema. Think of a database schema as a type of data structure. The size and complexity of your database schema depends on the size of your project.

The visual style of a database schema allows programmers to structure the database and its relationships properly before jumping into the code.

The process of planning a database design is called data modeling. DBAs are responsible for ensuring that data analysts and database users can easily access information. There are two main database schema types that define different parts of the schema: logical and physical. A logical database schema represents how the data is organized in terms of tables.

It also explains how attributes from tables are linked together. Different schemas use a different syntax to define the logical architecture and constraints.

Note: Integrity constraints are a set of rules for a DBMS that maintain quality for data insertion and updates. To create a logical database schema, we use tools to illustrate relationships between components of your data.

This is called entity-relationship modeling ER Modeling. It specifies what the relationships between entity types are. The schema diagram below is a very simple ER Model that shows the logical flow in a basic commerce application. It explains a product to a customer who buys a product. This is the id that uniquely identifies the entry in a document or table. The FK in the diagram is the foreign key.

This is what links the relationship from one table to the next. Entity-relationship models can be created all sorts of ways, and online tools exist to assist in building charts, tables, and even the SQL to create your database from your existing ER Model. This will help to build the physical representation of your database schema. The physical database schema represents how data is stored on disk storage. In other words, it is the actual code that will be used to create the structure of your database.

In MongoDB with mongoose, for instance, this will take the form of a mongoose model. Compared to the logical schema, it includes the database table names, column names, and data types. Any given client connection to the server can access only the data in a single database, the one specified in the connection request.

Note: Users of a cluster do not necessarily have the privilege to access every database in the cluster. Sharing of user names means that there cannot be different users named, say, joe in two databases in the same cluster; but the system can be configured to allow joe access to only some of the databases. A database contains one or more named schemas , which in turn contain tables.

Schemas also contain other kinds of named objects, including data types, functions, and operators. The same object name can be used in different schemas without conflict; for example, both schema1 and myschema can contain tables named mytable. Unlike databases, schemas are not rigidly separated: a user can access objects in any of the schemas in the database he is connected to, if he has privileges to do so. Third-party applications can be put into separate schemas so they do not collide with the names of other objects.

Schemas are analogous to directories at the operating system level, except that schemas cannot be nested. Give the schema a name of your choice. For example:. To create or access objects in a schema, write a qualified name consisting of the schema name and table name separated by a dot:. This works anywhere a table name is expected, including the table modification commands and the data access commands discussed in the following chapters.

For brevity we will speak of tables only, but the same ideas apply to other kinds of named objects, such as types and functions. If you write a database name, it must be the same as the database you are connected to. See Section 5. Often you will want to create a schema owned by someone else since this is one of the ways to restrict the activities of your users to well-defined namespaces. The syntax for that is:. You can even omit the schema name, in which case the schema name will be the same as the user name.

In the previous sections we created tables without specifying any schema names. By default such tables and other objects are automatically put into a schema named "public". Every new database contains such a schema. Thus, the following are equivalent:.

Qualified names are tedious to write, and it's often best not to wire a particular schema name into applications anyway. Therefore tables are often referred to by unqualified names , which consist of just the table name. The system determines which table is meant by following a search path , which is a list of schemas to look in.

The first matching table in the search path is taken to be the one wanted. If there is no match in the search path, an error is reported, even if matching table names exist in other schemas in the database. The first schema named in the search path is called the current schema. The first element specifies that a schema with the same name as the current user is to be searched. If no such schema exists, the entry is ignored.