How Web Applications Function

 A web application is an application that runs on the web and is accessible via a web browser. In over simplified terms; it is a website that can do stuff. A website’s primary role is to show; displays information. The web app on the other hand can perform tasks like; log-in, send messages and save data.

The basic structure of a conventional web application is divided into three sections. These are; presentation, application and storage. All three work together to deliver the function of a web application. The sections can also be referred to as ‘layers’. 

The presentation layer is also called ‘front-end’. The front-end of an application is anything that a user sees and interacts with. It’s primary goal is to present. So anything that a user sees and interacts with is basically the front end. When it functions independent of other layers, technically, is a website.

Making the presentation layer is a combination of specialized scripting languages. HTML(Hyper-Text Mark Up Language) is used to place content into place. CSS(Cascading Style Sheets) is used to style the page and JavaScript is used to program behavior. These three make up all you see from a browser. Should you want to get a deeper understanding of this; check out this article.
 
 Applications exist to manipulate, store and retrieve data. Data is a record made. For example; username, subject, body and attachments are primary data attributes used in email applications. This data needs some sort of storage if it is to be retrieved later. Web apps deliver dynamic pages. That is; what you see keeps changing. The new content is constantly being retrieved and delivered to the front end from a database.

A database is as the name suggests; a base for data. This is the storage layer. Logically, a database can exist on it’s own and still serve storage purpose. The common language dominating this domain is SQL(Structured Query Language). This language is made of words like ‘select’, ‘where’, ‘order by’ and conditions like ‘Min’ and ‘Max’. Supported actions in abbreviation called CRUD (Create, Read, Update and Destroy) operations.
 
 If you remember from earlier, I did describe the front-end as a website. Then there is the database which can also function alone. The real power behind web applications comes in when the presentation layer is connected to the storage layer. This is where the application layer comes into play, connecting the presentation layer to storage.

The application layer holds most of the logic that the application needs. In specific circles, it is called the ‘controller’. The controller listens to requests from the presentation layer, processes them according to need, contacts the database and vise versa. This layer is complex compared to the previous mentioned. It essentially does all the ‘thinking’.

Say a user wants to log in. The user will use the presentation layer to pull a log-in page, user enters an email, a password and presses the OK button. This sends a request to the application layer which in turn sends a query to the storage layer. The query checks if there exists a record matching the email entered. If there’s is, it checks if the password attached to the email is true. If yes, it returns a ‘true’ to the application layer. Since the user is now confirmed, the application logic will then present the next page after login. This page is then received by the presentation layer and the user is now logged in. 
 
 To sum it up, a web application allows users to interact with data in an application using a browser. The user will always use the presentation layer to interact with the application. Logic is handled by the application layer and all the data goes to storage.
 
 That’s the basic operation of a web application.