Other Types of Databases
The relational database model is the most used database model today. However, many other database
models exist that provide different strengths than the relational model. The hierarchical database model,
popular in the 1960s and 1970s, connected data together in a hierarchy, allowing for a parent/child
relationship between data. The document-centric model allowed for a more unstructured data storage by
placing data into “documents” that could then be manipulated.
Perhaps the most interesting new development is the concept of NoSQL (from the phrase “not only
SQL”). NoSQL arose from the need to solve the problem of large-scale databases spread over several
servers or even across the world. For a relational database to work properly, it is important that only one
person be able to manipulate a piece of data at a time, a concept known as record-locking. But with today’s
large-scale databases (think Google and Amazon), this is just not possible. A NoSQL database can work
with data in a looser way, allowing for a more unstructured environment, communicating changes to the
data over time to all the servers that are part of the database.