Three-tier model is the most common form of multi-tier architecture used in software engineering. Generally, a three-tier model is a software design pattern and a form of software architecture (Three-Tier Architectures, 2008). Three-tier model is used as client-server architecture, whereby the database, business rules, user interface, and data access are created and maintained independently. In web development, three-tier is used to refer to websites. Commercial websites for big business entities as well as government agencies involved in trade and commerce use three-tier model to develop their websites (Three-Tier Architectures, 2008).

In web development, three-tier model allows a web user to interact with a computer using a desktop or a workstation through the help of accustomed graphical user interface. A three-tier model usually has three levels - tiers. They are presentation, application, and data tiers (Sheriff, 2002). Presentation tier is the topmost level, which presents information to the users. It communicates with other tiers in order to provide an output as requested by a user. Application tier, also known as middle tier, data tier, or logic tier is an independent level but it is pulled from the presentation tier. Its function is to control the functionality of the presentation tier by undertaking comprehensive processing. The lowest level is the data tier, which is made of database servers. Its function is to store and retrieve data in a neutral and independent manner (Sheriff, 2002).

Three-tier model suffers minimal threats from external systems. This is because all its three levels work independently from each other. In case of external threat/interference, only the concerned tier is affected, thus allowing the developers to repair or modify the affected tier as opposed to rewriting an entire application (Three-Tier Architectures, 2008).

The most common forms of database include analytical and operational database (Ferguson, 2010). Analytical database is used to store, report, and document information, which is not necessarily recent. Common information found in analytical database includes financial, sales, and marketing information. Operational database stores data on real-time basis. That is, data found in operational database is recent. Example of data found in operational database is a store’s data where information about customers’ orders and inventory are stored on real-time basis (Ferguson, 2010). Out of the two forms of database, operational database is likely to become more important in the future. This is because as time goes by, database users are increasing, with their needs for quick, easy, and real time access to data increasing as well.

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