HTML and CSS Reference
In-Depth Information
What is a web application?
A reasonable question to ask is “What is a web application, and how is it different from a
web site?” Even the opening section of the HTML5 specification states that it is designed to
address “…the vague subject referred to as web applications”.
There is no definitive answer to this question, but the web application developed in this topic
exhibits the following characteristics:
• It uses a web browser for its user interface.
• It allows users to perform actions and manipulate data without performing screen refreshes.
• It is interactive, and responds promptly to user actions.
• It stores data on behalf of a user, either on the client or the server.
• If it needs to access a web server, it does so using asynchronous AJAX calls.
• It favours asynchronous APIs over synchronous APIs.
• It may be available even when the user is not connected to the Internet.
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It will be important throughout this topic that you understand the difference
between an asynchronous and a synchronous API. Although this topic will offer
many examples, the basic difference between the two is:
• A synchronous API waits for a response, and blocks everything else from hap-
pening in the application until that response is received.
• An asynchronous API does not wait for a response, but instead asks to be noti-
fied when a response is available. As a result it does not block other functionality
in the application from progressing.
The HTML5 specification suggests that web applications will also exhibit the following fea-
tures:
• They are used on an occasional basis, or on a regular basis but from different locations.
• They have low CPU requirements.
