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A NoSQL database provides a simple, lightweight mechanism for storage and retrieval of data that can under certain conditions provide higher scalability and availability than traditional relational databases . The NoSQL data stores use looser consistency models in order to achieve horizontal scaling and higher availability. Some authors refer to them as "Not only SQL" to emphasize that some NoSQL systems do allow SQL -like query language to be used. NoSQL database systems are often highly optimized for retrieval and appending operations and often offer little functionality beyond record storage (e.g. key–value stores). The reduced run-time flexibility compared to full SQL systems is compensated by marked gains in scalability and performance for certain data models. In short, NoSQL database management systems are useful when working with a huge quantity of data when the data's nature does not require a relational model.
An XML database a data persistence software system that allows data to be stored in XML format. These data can then be queried , exported and serialized into the desired format. XML databases are usually associated with document-oriented databases . Two major classes of XML database exist: [ 1 ]
A graph database uses graph structures with nodes, edges, and properties to represent and store data. By definition, a graph database is any storage system that provides index-free adjacency. This means that every element contains a direct pointer to its adjacent element and no index lookups are necessary.
A document-oriented database is a computer program designed for storing, retrieving, and managing document-oriented, or semi structured data , information. Document-oriented databases are one of the main categories of so-called NoSQL databases and the popularity of the term "document-oriented database" (or "document store") has grown [ citation needed ] with the use of the term NoSQL itself. In contrast to well-known relational databases and their notions of "Relations" (or "Tables"), these systems are designed around an abstract notion of a "Document".
Is relational database dying? Why a model affirmed and finally consolidated over years is now object of discussion? Which alternatives exist and how they can match your needs in practical situations?