A three-tier model is a useful overview of the process of developing web applications. Each tier represents an essential part of the overall process. Developers have labeled them in many ways, but for a summary, a useful description is the user tier, the business tier, and the information tier.
The information tier is the data used to carry out the jobs that one designs the web application to do. It can be a data warehouse that stores things, or a database that must interact with variables to produce results. The business tier is the purpose of the application, the logic of the interactions comes from purposes. In a sales environment, the purpose is to match search queries with items, then orders with inventory or supplies. The final layer is the user tier consisting of the arrangements for access by browsers and interaction with consumers.
In outline form, the development process for applications flows from making a concept or vision, devising a project plan, implementing the plan, and testing the system. The planning stage involves determining the problems the application must solve. The plan requires a functional analysis of the parts of the application, for it establishes how they will look and interact. This part of the effort establishes the data variables, entities and coding procedures for the remainder of the project. For example, in a sales situation, an order would be an entity. This analysis guides the plan including selecting a language for writing code such as Python or Ruby on Rails.
The code must be able to handle the parts and interactions required by the functional analysis. The project plan then can detail timelines and schedules for producing code. There are many programs available to shorten the tasks of producing code, some work automatically so that non-programmers can create useable code. Testing is crucial to the effectiveness; the application must work under a variety of conditions. Server integration is another factor in application development and the choices include Microsoft Windows frameworks that on the server-side use leading languages like PHP and Ajax.
The three tiers form the overall framework for application development. The database tier contains the entities and elements. The business tier provides the ways in which entities must interact as required by the business logic. The user tier is critical to success because it is where consumers must engage and carry out the business purposes, such as sales of merchandise. The user interface must be simple, quick, and reliable, but at the same time, unique and not a carbon copy of the competition.
Current trends in application development require additional tiers due to increased complexity. Developers often need to use a multilayer approach that makes additional divisions in the business logic grouping, or that link directly to the database for various forms of search or scalability. Cloud computing has changed application development as it presents applications in Software As A Service format. Referred to as SaaS, these applications require software for licensed browser access.