Mumbai University > Computer Engineering > Sem 5 > SOOAD

Marks: 10M

Year: Dec 2014

Three-tier architecture:

1. Three-tier architecture is an architectural deployment style that describe the separation of functionality into layers with each segment being a tier that can be located on a physically separate computer. They evolved through the component-oriented approach, generally using platform specific methods for communication instead of a message-based approach.
2. This architecture has different usages with different applications. It can be used in web applications and distributed applications. The strength in particular is when using this architecture over distributed systems. In this course work, I will furthermore invest this through the example of three-tier architecture in web applications.
3. Structure:- Using this architecture the software is divided into 3 different tiers: Presentation tier, Logic tier, and Data tier. Each tier is developed and maintained as an independent tier.

• Presentation Layer

  In the presentation layer the user interaction takes place as defined before. The user enters the address in the web browser and in the browser the URL is decoded into protocol/host/file, i.e. host name converted to IP address. Then an issue request is sent to remote server using appropriate protocol (usually HTTP). Also a returned HTML from the logic tier might be accepted. In the presentation layer interaction with client side scripts (e.g. using DHTML) is supported and user input of variety controls on the form are accepted.

• Logic Tier

  In the logic Tier the application’s functionality is done by performing detailed processing of data from presentation layer. Server such as Apache (or IIS) or Server Script (such as PHP) can be used to support this. With Server (Apache or IIS) the appropriate action to be taken is identified, such as fetching a file, or passing request to an interpreter. Also it sends an output back to caller in MIME package. As such support for thousands for concurrent users, multithreading (allow multiple processor to run concurrently) and caching (holding results in a temporary store to reduce recalculation) is achieved).

  With Server script (example in PHP) interacting with server such as accessing input or generating input is done. It interprets the requests according to business rules and past transactions from this client, and requests appropriate data from the persistence layer. It also computes the derived data and creates HTML (or GIF…) for the page.

• Data Layer

  This tier consists of database servers. The interaction with the database is done using standard languages such as SQL queries using database specific protocol over TCP/IP. The data structures (for example tables) are defined and modified themselves, that insertion, updating and deleting of data for example. Data maintenance should be maintained with backup and recovered. Access to compilation of queries should be optimized, with indexing or replication of tables. An example of technology using this would be .NET that is built into the .NET framework, as ADO.NET contains a mechanism to query data out of the database and return it to the caller in a connected or disconnected fashion.