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Introduction to Database Systems
11: Client/Server Architecture
11.1: Introduction and Background to Client/Server Systems and Multi-tier Architecture

11.1: Introduction and Background to Client/Server Systems and Multi-tier Architecture

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6.1 - Introduction and Background to Client/Server Systems and Multi-tier Architecture

The client/server model is the standard model of networked traffic in today's computing and database systems. The client/server model was designed with world wide web services in mind and to allow for servers to provide service to end user devices all over the network. This methodology has been adopted as the standard for content publishing and receiving by modern network systems.

Figure \(\PageIndex{1}\): A graphic demonstrating the architecture of client/server systems. From “*An Introduction to Client/Server Computing*” by Yadav SC, Singh SK, 2009.

For databases, the model of client/server is ideal because the database can easily serve multiple users at the same time through standardized calls for information. If multiple users are looking to fetch the same files on a routine basis, tools can be deployed which monitor the trends of usage and allow for IT administrators to beef up the systems which serve those files, reducing wait times and increasing overall system performance. Similarly, for systems or databases which are accessed less frequently, those costs can be avoided.

Prior to the client/server architecture, peer-to-peer networking was used. This means that for every request to send or receive, devices would communicate one-to-one, and for each transaction of data, this process had to be repeated. By taking on the role of a “server”, a system can handle more than one call at once, drastically improving throughput and efficiency. Using the client/server model gives rise to a very specific set of requirements when designing a transport layer protocol. Generally, a transport layer protocol needs to cover all of the following requirements: a connection between a client and server, an interaction between the client and server, authentication of the client and server, and a checksum or other method to maintain data integrity after having sent and received packets.

Multi-Tier Architecture (MTA) can be generalized as a separation and duplication of a server/database system by decentralizing data and compute resources. MTA is used to improve reliability and throughput, similarly to client/server architecture. As such, an MTA environment will almost certainly use client/server communication.

MTA systems are composed of 6 basic layers (Wall, D, Morgan Kaufmann):

Persistence: The database which serves files to the applications that service the clients or users.
Accessor: Typically, the SQL server. Not the disks in the database, but the part of the database which does the thinking.Logic: The applications which the users interact with, in turn providing instructions to the database from which files are requested.

Presentation: Systems applications which package data from the database into web browser languages such as HTML or XML.
Requester/consumer: The web browser itself; this is on the client side.
Elsewhere: The sources of information hosted on other platforms, such as AWS, Azure,

or GCP, or other sources of HTML content that are not native.

Figure \(\PageIndex{1}\): A graphic demonstrating the architecture of multi tier architecture.