What is meant by NoSQL?

• No "official" definition exists

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  • No SQL, or Not Only SQL
  • Non-relational, distributed, open source, scalable

• Does not use relational model

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  • No tables, rows, columns and relations
  • Different models used:
  • Column, document, key-value and graph
  • Other models:
  • Multimodel (OrientDB), Object (db4o), Grid/Cloud, XML (Berkeley DB XML), Multidimensional (GT.M), Multivalue (TigerLogic PICK)

• No fixed schema

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  • Lowest unit of MongoDB data is a "document"
  • Uses a JSON document as basis
  • Allows considerable flexibility
  • JSON is converted to BSON for storage

• Driven by "big data"

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  • Scales extremely well
  • Works well in clustered/cloud environment
  • Google Bigtable
  • Amazon SimpleDB

• Examples

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  • MongoDB, CouchDB, RavenDB : Document
  • Cassandra, Apache HBase (Hadoop) : Column
  • Redis, Riak, DynamoDB : Key/Value
  • Neo4j, Titan : Graph