NoSQL Databases: Design & Types

Instructor: Martin Gibbs

Martin has 16 years experience in Human Resources Information Systems and has a PhD in Information Technology Management. He is an adjunct professor of computer science and computer programming.

There are alternatives to SQL databases and relational databases in general. This lesson covers these alternate database management systems, referred to as NoSQL databases.

An Alternative to SQL

Yes, we actually have no SQL Relational Databases!

It may seem like the landscape of database management systems is dominated by SQL and relational database management systems. A relational database is made up of tables, records and columns, and the tables are connected together through specific relationships. Once built, they can be very complex and quite rigid; changing the relationships is often difficult. As the database increases in scope, the number of tables and relationships also increase. How are you supposed to manage data that's not necessarily organized/structured?

Enter NoSQL.

NoSQL does not mean the absence of SQL; instead it means Not Only SQL. In other words, we are not limited to a single option to store and retrieve the data. As its name implies, there is no fixed definition for what NoSQL is or does, but the following concepts can help us understand what NoSQL is (and isn't):

  • No relational model
  • Data can be clustered
  • Most solutions are open-source
  • Built for the Web
  • Lack of a schema

Why NoSQL?

Since everyone is on the Web these days, it doesn't make a lot of sense to keep the database separate from the applications it servers. Think about sites like Facebook - their data storage needs are completely different than those of a large organization's administrative systems. The relational model just doesn't work as well for that large amount of data.

In part, this is because the relational model is fairly rigid, which means that changing an existing structure can be time-consuming. NoSQL, on the other hand, is very flexible. It can accept different data types with ease, including structured or unstructured. Structured data is arranged in neat rows and columns, and can be very tidy, if not huge and complex. Unstructured data, on the other hand, isn't organized; it doesn't follow the strict patterns found in relational databases.

Relational databases can also have very large tables, leaving them with records that can be bloated with huge numbers of columns. NoSQL, as the visuals in this lesson will show, isn't tied to this rigid nature. It offers things like a clustered approach that can actually improve performance.

Types of NoSQL

There are four broad categories of NoSQL databases: key-value, column family, document, and graph.

Key-Value Databases

NoSQL Sample
NoSQL Sample

A key-value database is considered the backbone of NoSQL databases. The key-value database matches a key to a value; there are no relationships or structures. In the previous figure, the key is the customer ID, which grants access to that customer's orders.

This is the easiest data source to integrate with: A client can retrieve a key value, update a key value, or delete a key. The database doesn't care what is stored in the bucket; only the application needs to know what was stored. In the previous figure you can see that if you have the Customer ID key, you can get to all the data stored about that customer, from their address to the product the ordered. You could even add a data element, such as preferred name, to the Order bucket. This is a no-no in a relational model, but the NoSQL database doesn't care.

Accessing key-value database management systems is usually very fast, and this speed doesn't diminish as the database grows.

Column Family Databases

column family no sql

Unlike the specific key/row relationship found in relational databases, column-family databases store data in groups of rows. Any number of columns can be associated with the row key. This way we can access related data that is often queried together. For example, we can capture the user of a web application's profile when they are signing in.

This solution alleviates the column bloating that can be found in relational databases; again, we see data in clusters and nodes rather then rigid structures.

Document Databases

Document Databases
document no sql

When you have very deep, complex data structures, the document-based data store is a great option.

Here's a very simple example of how this might look to represent an album:

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