Intro to Document Stores

What is NoSQL?

NoSQL refers to the storage and retrieval of persistent data that are not stored in related tables.


DB Management Systems that fall under this term are 

Key-Value, Graph, or Document Stores

What is a

Document Store?

a.k.a. Document-oriented Database

Document Store

Every database management system that utilizes the idea of storing data as "documents", store these documents in the following formats


  • JSON
  • BSON
  • XML
  • YAML

A Sample Document

  "_id" : ObjectId("55affc8487df4e4899702589"), 
  "username" : "qui-gon-jinn-and-juice",
  "firstName" : "Anakin",
  "lastName" : "SkyTroller",
  "password" : "padawonton"

Tables, Records, Collections, Documents,

what's the difference?

Tables and Collections

RDBMS stores records as rows in related tables 

Document-Oriented DBs store Documents in unrelated Collections

Tables define columns, their data type, have keys and constraints.

Collections are schema-less at the db layer.

Tables and Collections, cont.

Tables can be indexed

Collections can be indexed 

Indexes increase the performance of queries.

db.jedis.createIndex({ name : "text"});
db.weapons.createIndex({ weight : 1 });
CREATE INDEX jedi_name_idx ON jedis (name);

Records and Documents

Tables have a predefined schema that all contained rows must abide by. Each column is defined with strict data types

Documents store unstructured data in fields that do not have to conform to a predefined schema.

Rows in tables must follow the predefined schema, if the table schema changes, every row in the table adopts these changes.

Individual Documents can be updated at any time to remove existing or add new fields.

db.jedis.insert({ username: "mace808", firstName:"Mace"});
db.jedis.insert({ name: { first: "Obi Wan", last: "Kenobi"}, force : 1200 });
  id serial,
  username varchar(50) NOT NULL,
  firstName varchar(50) NOT NULL,
  lastName varchar(50) NOT NULL,
  password varchar(32) NOT NULL,
  weapon_id integer,

Records and Documents, cont.

Tables can set foreign key constraints to track relationships

Documents do not have foreign keys to manage relations

Table schemas can be normalized to reduce redundancy and disk usage.

Documents can be denormalized to increase data duplication and disk usage, and can increase data read/retrieval performance.

  id integer PRIMARY KEY,
  customer_id integer REFERENCES products (id),
  price integer

Records and Documents, cont.

Tables can join other tables using foreign keys, to include related data in the resulting rows.

Documents can embed other documents!

Table rows cannot embed other rows.

  "_id" : ObjectId("55affc8487df4e4899702589"), 
  "username" : "qui-gon-jinn-and-juice", 
  "firstName" : "Anakin", 
  "lastName" : "SkyTroller", 
  "password" : "padawonton" 
  "weapon" : { 
    "_id" : ObjectId("21zffc8487df4e4899702589"),
    "name" : "Light Saber",
    "weight" : 59.634
  "friends" : [
    { "_id" : ObjectId("44bffc8487df4e4899702589"), ... }, 
    { "_id" : ObjectId("33cffc8487df4e4899702589"), ... }, 


What's the difference?

SQL refers to any of the database systems where data is stored in tables that support relations.


NoSQL refers to any of the databases that manages data in non-relational Document, Key-Value, Graph, or Wide-Column stores.

Most features of RDBMS can be used synonymously with the term: SQL.


Most features of Document, Key-Value, Graph, and Wide-Column data stores can be used synonymously with term: NoSQL.

SQL databases

use the declarative Structured Query Language for defining and manipulating the data.



NoSQL databases

 use an unstructured query language that varies from system to system, and can be imperative. 

var usersCur = db.users.find();
var firstUser =;
var firstUserName = firstUser.username;
SELECT username FROM users LIMIT 1;

SQL databases

store data in tables with a fixed schema with strict types


NoSQL databases

 store data in collections where each entry (document, value, node, or row) can have dynamic schemas, they can differ from entries belonging to the same collection

SQL databases

most rdbms are ACID compliant

Atomicity, Consistency, Isolation, Durability,

and support transactions.


NoSQL databases

 most do are not ACID compliant, in favor of performance and scalability

SQL databases

typically use vertical scaling strategies.

the more data you have to store,

the bigger your server gets.


NoSQL databases

 are designed to scale horizontally,

across multiple servers.

SQL products

  • MySql
  • Postgres
  • MariaDB
  • MS-SQL
  • Oracle
  • Sqlite 
  • more...

NoSQL products

  • MongoDB
  • Redis
  • Cassandra
  • Riak
  • CouchDB
  • BigTable
  • Hbase
  • more...


  • Do you need the consistencies and reliability provided by being ACID compliant, having constraints, and transactions?
  • Will you be analyzing aggregate data?
  • Is a static typed schema ok?
  • Do you need/want to write SQL?


  • Do you need to scale easily?
  • Is "eventual consistency" ok?
  • Do you need non-mission critical data at served at higher performance?
  • Will your schema change?
  • Is it ok to not write SQL?

Which to Choose?

Intro to NoSQL

By Joe Karlsson

Intro to NoSQL


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