This chapter will discuss Not Only SQL (NOSQL) technologies in general, compares different NOSQL databases, discusses the limitations with Relational Database Management Systems (RDBMS), and gives an understanding of how different databases behave for different variants with different amounts of data in the database. This will lay a foundation for the thesis in general and will evaluate some of the related work in this context. Related Work
The thesis “No Relation: The Mixed Blessings of Non-Relational Databases”  gives a good understanding of non-relational data stores. The author discusses the non-relational data stores in detail and how they differ from relational data stores. Comparison of both data models in terms of strengths and weaknesses has also been discussed. Non-relational data stores gained popularity when developers started to realize that there was a need to find an alternative, then non-relational data store and new efficient architectures were developed to make the data read and write fast such as in memory data store and process. As the thesis is more than three years old, some parts are already outdated as new architectures have been developed or modified for good read and write performance. For example, the author discusses super columns in Cassandra which are not recommended to use anymore.
The thesis “Cassandra”  gives a good understanding of Apache Cassandra. The author identifies the limitations that exist in RDBMS and how these limitations can be solved using Apache Cassandra such as Scalability. Moreover, differences between Cassandra and RDBMS have also been discussed from different point of views. As thesis is more than two years old, new concepts are not discussed such as Cassandra data store, Cassandra architecture, Cassandra replication strategy, Cassandra data partition, how Cassandra handles read and write requests, and different indexes techniques in Cassandra for efficient data access. Cassandra is an open source project which makes it strong candidate to progress in the next few years. Many wrappers over Remote Procedure Calls (RPC) client have developed for different programming languages described in High level clients in Cassandra5.13High level clients in Cassandra which are also not discussed.
There is no doubt that NOSQL databases are getting popularity, but according to Database Administrators (DBAs) NOSQL has an immature data store. NOSQL proponents react with the argument that RDBMS does not scale large data volume well. The author has not found any example where NOSQL has been used to store financial data. Kristof Kovacs blog NOSQL Database Comparison  compares different popular NOSQL databases and identifies the situation in which they are best to use. According to author, Apache Cassandra is mostly suited for banking and financial industry .
The next section discusses some of the theoretical basis that would critical as part of this thesis and will put forward some of the important terminologies that will be used as part of this project.
Relational Database Management System (RDBMS)
Relational Database Management Systems (RDBMS) is based on relational model which was introduced by E. F. Codd. RDBMS is the basis for Structured Query Language (SQL) and modern database systems like Oracle, MS SQL Server, MySQL, and PostgreSQL . In general, RDBMS provides following features: * Data are stored in tables.
* Data storage is in the form of rows and columns.
* Primary keys are used to uniquely classify the rows.
* Indexing facility makes the data retrieval faster.
* Databases allow the creation of views or virtual tables. * Primary and foreign keys can be used to define relationship between two entities, i.e. the existence of a common column between two tables. * Multi-user accessibility
In Relational Database Management Systems (RDBMS), the data are stored in objects...
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