The NoSQL Key-Value database type uses a hash table in which a unique key points to an element. They can be organized into logical groups, requiring uniqueness within their boundaries. This allows you to use identical keys in different logical groups. Some database implementations provide caching mechanisms that significantly increase their performance.
All you need to work with the items stored in the database is a key. The data is stored as a JSON string or BLOB (large binary object). One of the biggest disadvantages of this form is the lack of consistency at the database level. This can be added during the development of a NoSQL database by programmers with their own code, but it also requires more effort, due to the complexity of implementation and time. The most famous NoSQL database built on a key value store is Amazon DynamoDB.
Document stores are similar to key value stores in that they do not contain a schema and are based on a value model. So, both types have the same advantages and disadvantages. Both lack consistency at the database level, which does not allow applications to provide more reliable functions. Nevertheless, there are some key differences between them. In document stores, values (documents) provide the encoding for the stored data. These encodings can be XML, JSON, or BSON (binary JSON). The most popular database application that uses a document store is MongoDB.
In the Column Family database, data is stored in columns, not in rows, as is done in most relational database management systems. A column store consists of one or more column families that logically group certain columns in the database. A key is used to identify and specify the number of columns with a keyspace attribute that defines its scope. Each column contains tuples of names and values, ordered and separated by commas.
Column stores provide quick read/write access to the stored data. In it, the columns of a row correspond to a single column and are stored as a single disk record. This provides faster access during read/write operations. The most popular databases that use NoSQL database column storage are examples: Google BigTable, HBase, and Cassandra.
The NoSQL Graph Bd database uses the structure of an oriented graph to represent data. A graph consists of edges and nodes.