NoSQL

Key-Value Stores

• Data model: (key, value) pairs
• Interface: extremely simple
  1. Operations: Insert(key, value), Fetch(key), Update(key), Delete(key)
  2. Some allow (non-uniform) columns within value.
  3. Some allow Fetch on range of keys.

• Implementation: efficiency, scalability, fault-tolerance
  • Records distributed to nodes based on key
  • Replication
  • Single-record transactions, "eventual consistency".

• Example Systems (as of Nov 2011)
  • Google BigTable
  • Amazon Dynamo,
  • Cassandra
  • Voldemort
  • HBase

Document Stores

• Data model: (key, document) pairs
  • document: JSON, XML, other semistructured formats.

• Interface
  • Basic operations: Insert(key, value), Fetch(key), Update(key), Delete(key)
  • Also Fetch based on document contents (very system/format- specific)

• Example Systems (as of Nov 2011)
  • CouchDB
  • MongoDB
  • SimpleDB

Graph Database Systems

• Data model: nodes and edges
  • Nodes may have properties (including ID)
  • Edges may have labels or roles

• Interface
  • Interfaces and query languages vary
  • Single-step vs "path expressions" vs full recursion

• Example Systems (as of Nov 2011)
  • Neo4j
  • FlockDB
  • Pregel
  • RDF "triple stores" can map to graph databases