A 3-tier
application architecture is a modular client-server architecture
that consists of a presentation tier, an application tier and a data tier.
The data tier stores information, the application tier handles logic and the
presentation tier is a graphical user interface (GUI) that communicates with
the other two tiers. The three tiers are logical, not physical, and may or
may not run on the same physical server.
Presentation tier - This tier, which
is built with HTML5, JavaScript and cascading style sheets (CSS), is deployed
to a computing device through a web browser or a web-based application. The
presentation tier communicates with the other tiers through application
program interface (API) calls.
Application tier - The application
tier, which may also be referred to as the logic tier, is written in a
programming language such as Java, Python or Ruby and contains the business
logic that supports the application's core functions. The underlying
application tier can either be hosted on distributed servers in the cloud or
on a dedicated in-house server, depending on how much processing power the
application requires.
Data tier - The data tier
consists of a database and a program for managing read and write access to
the database. This tier may also be referred to as the storage tier and can
be hosted on-premises or in the cloud. Popular database systems for managing
read/write access include MySQL, Oracle, PostgreSQL, Microsoft SQL Server and
MongoDB.
The benefits of using a 3-layer architecture include improved scalability,
performance and availability. With three tiers or parts, each part can be
developed concurrently by a different team of programmers coding in different
languages from the other tier developers. Because the programming for a tier
can be changed or relocated without affecting the other tiers, the 3-tier
model makes it easier for an enterprise or software packager to continually evolve
an application as new needs and opportunities arise. Existing applications or
critical parts can be permanently or temporarily retained and encapsulated
within the new tier of which it becomes a component.
3-tier application programs may also be referred
to as n-tier programs. In this context, the letter "n" stands for
'a number of tiers.'
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