RDBMS - Relational Database Management System

What is an RDBMS?

RDBMS stands for relational database management system—a software system that enables you to define, create, maintain, and control access to relational databases. It is the underlying part of the interface layer that helps you store and work with data.

Now let's address the definition of a relational database to see what makes it so special. A relational database is the most popular type of database that stores and provides access to data points that are related to one another. In relational databases, data is arranged and stored in tables consisting of columns and rows. And of course, you have the intuitive and flexible Structured Query Language to manipulate databases.

Work model

How does the relational model work?

Like we mentioned above, RDBMS stores data in tables. Each row in a table is a record with a unique ID, which is called primary key. The columns of a table contain attributes of the data. Since each record typically has a value for each attribute, it becomes easy to form flexible relationships between data points.

Let's take a look at the basic notions associated with relational databases.

Primary key is a unique ID that identifies each row of a table.

Foreign key is a field (or multiple fields) in one table that refers to a primary key in another table. It helps establish relations between tables.

View is a virtual table that does not store data; instead, it presents a certain data output that is computed from underlying tables.

Index is a data structure that contains a copy of a column (or multiple columns) from a database table that is ordered to accelerate database retrieval operations on the original column.

Structured Query Language (SQL) is a domain-specific language used for storing, retrieving, and manipulating data—a standard for relational databases.

SQL query is a request for information from an RDBMS. Users write and execute queries to retrieve, add, modify, and delete data from relational databases.

Types of relationships

There are three main types of relationships between tables that ensure the absolute flexibility of the relational database model.

One-to-one relationships

One-to-one relationship is when a single record in table A is related to one (and only one) record in table B.

One-to-one relationships

One-to-many relationships

One-to-many relationship is a bit more complex: a single record in table A is related to multiple records in table B.

One-to-many relationships

Many-to-many relationships

Finally, the most sophisticated example is many-to-many relationship, when multiple records in table A are related to multiple records in table B.

Many-to-many relationships

Relational notations

Now that we have described the main types of relationships, we can add a few words on how they are represented on entity-relationship diagrams—via relational notations.

IDEF1X notation

IDEF1X stands for integrated definition for data modeling. Diagrams of this type show entities connected to each other without relationship symbols. The attributes for any entity are listed as part of a table inside each entity shape instead of separate symbols.

IE notation

IE notation (also known as crow's foot notation) uses graphical symbols to show the 'many' side of relationships.

Parent record Child record Example
1 (exactly one) 0..N (zero, one, or more) Notation example 1
1 (exactly one) 0..1 (zero or one) Notation example 2
0..1 (zero or one) 0..N (zero, one, or more) Notation example 3
Data 0..1 (zero or one) 0..1 (zero or one) Notation example 4

Key features of RDBMS

Structured and interrelated data

Structured and interrelated data

Data in relational databases is stored in a well-structured and easily understandable table format. Meanwhile, versatile relations between tables and the use of SQL to write queries of different complexity contribute to the flexibility of data management.

ACID support

ACID support

ACID (which comprises Atomicity, Consistency, Isolation, Durability) is a well-known set of properties of database transactions meant to guarantee data validity despite errors, failures, and other possible mishaps. Relational databases deliver full ACID support.

Multi-user access

Multi-user access

Relational databases provide multi-user access along with privileges that allow database administrators to have complete control over activities in databases and grant different levels of access to other users.

Ease of use

Ease of use

Besides the overall convenience of storing, accessing, and managing data in tables, we should mention a multitude of database tools that offer intuitive GUIs and make daily development and administration of databases rather easy even for newcomers.


Advantages and disadvantages of RDBMS

The vast capabilities and benefits of relational database management systems make them perfect for modern software solutions. However, there are also several disadvantages to take note of.

The pros:
  • Flexible data management
  • Integrity and security of sensitive data
  • Reliable data storage, easy backup and recovery
  • Compliance with data protection standards and regulations (such as GDPR)
  • Fast integration with commercial software and streamlined development cycle
The cons:
  • Hardware and software costs
  • Scalability can be pricey
  • Regular updates of your RDBMS may require regular database maintenance
  • Effective work with RDBMS requires professional expertise of database developers and administrators

What are the most popular relational databases in 2022?

RDBMS proved to be the optimal choice for data management in software solutions from nearly every business domain. Examples of the most popular relational database management systems include Oracle, MySQL, Microsoft SQL Server, PostgreSQL, SQLite, and MariaDB.

For each of these, there is a variety of database tools that help tackle routine development and administration tasks with ease and convenience.

Oracle Database

Oracle Database is renowned for its overall complexity, rather difficult management, and high costs. However, in exchange it offers high portability and backward compatibility, easy recovery, and excellent performance.

Oracle

MySQL

MySQL is one of the leading relational database management systems that boasts a huge community. Although MySQL is generally a free and open-source RDBMS, it is also available under a variety of proprietary licenses.

MySQL

SQL Server

SQL Server is pretty much the world's most advanced commercial RDBMS, developed by Microsoft and perfectly tailored to corporate IT environments. It delivers secure and efficient data storage and an infrastructure with multiple additional services.

SQL Server

PostgreSQL

PostgreSQL is an open-source RDBMS that offers rich functionality, support for a wide variety of data types, and storage of schemaless data. The popularity of PostgreSQL is currently on the rise.

PostgreSQL

SQLite

SQLite is a fast and compact database engine; not a full-fledged piece of software, but rather a library that can be embedded in applications.

SQLite

MariaDB

MariaDB is a community-developed and commercially supported fork of MySQL that was designed to get improved performance and stability as well as adhere to the open-source policy. It is worth noting that MariaDB remains a capable drop-in replacement for MySQL.

MariaDB

How to choose the right relational database?

Commercial databases

  • High licensing costs
  • On-demand tech support
  • Regular updates supplied by the vendor
  • Reasonable for commercial software
Microsoft SQL Server
Microsoft SQL Server
IBM DB2
IBM DB2
Oracle Database
Oracle Database

Open-source databases

  • Open-source licensing
  • No official support
  • Large user communities
  • For commercial and non-profit software
MySQL
MySQL
MariaDB
MariaDB
SQLite
SQLite
PostgreSQL
PostgreSQL

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Administration and maintenance

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Not available
Not available

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