19
Lecture 4: Types of NoSql Databases
There are four kinds of NoSQL databases:
i). document databases e.g Mongo DB, XML Native DB
ii). key-value stores e.g. Amazon DynamoDB, ScyllaDB,
iii). column-oriented databases: Apache Cassandra
iv). graph databases.
The db language of NoSQL data bases differ depending on file storage type e.g XML Native
DB uses XQUERY, MongoDB uses Javascript etc
Document Databases
This type of data model allows you to store information as any type of data. This is in contrast
to SQL, which relies heavily on XML and JSON, and essentially ties the two together, and can
make any query inefficient (or less efficient). Since NoSQL doesn’t use a scheme, there’s no
need for relational data storage, and no need to tie those two together. there is a NoSQL data
model that is XML specific, if you want to go that route.
The document-based database is a nonrelational database. Instead of storing the data in rows
and columns (tables), it uses the documents to store the data in the database. A document
database stores data in JSON, BSON, or XML documents.
Documents can be stored and retrieved in a form that is much closer to the data objects used in
applications which means less translation is required to use these data in the applications. In
the Document database, the particular elements can be accessed by using the index value that
is assigned for faster querying.
Collections are the group of documents that store documents that have similar contents. Not
all the documents are in any collection as they require a similar schema because document
databases have a flexible schema.
Key features of documents database:
Flexible schema: Documents in the database has a flexible schema. It means the
documents in the database need not be the same schema.
Faster creation and maintenance: the creation of documents is easy and minimal
maintenance is required once we create the document.
