1. Client-Server Database Systems

A client is defined as a requester of services and a server is defined as the provider of services.
Today centralized systems act as server systems that satisfy requests generated by client systems.
Functionally database systems can be broadly divided into two parts:

• Front end: front end of a database system consists of tools such as SQL user interface, forms interfaces, reports generation tools, and analysis tools.  


• Back end: The back end of a database system manages query evaluation and optimization, access structures, concurrency control and recovery management.











2. Parallel Systems




In parallel processing, many operations are performed simultaneously and the computational steps are performed sequentially. It can process thousands of transactions per second.





There are four types of Architectural Models for Parallel Processing:

• Shared Memory (tightly coupled) architecture: Multiple processors share secondary (disk) storage and also share primary memory.


•  Shared Disk (loosely coupled) architecture: Multiple processors share secondary (disk) storage but each has their own primary memory.


• Shared Nothing: The processors share neither a common memory nor common disk.


• Hierarchical: this model is the combination of preceding three architectures.



3. Distributed Systems

Distributed database is a collection of multiple logically interrelated databases distributed over a computer network and a distributed database management system is a software system that manages a distributed database while making the distribution transparent to the user. Transparency means hiding the details of where the data is physically stored within the system.
Reasons for building a distributed database are sharing of data, autonomy, and availability.

Functions of distributed databases:

• Keeping track of data.


• Query Processing by a communication network.


• Security Management.


• Distributed Transaction Management


• Database Recovery.