Question related to XML

1. How important is <?xml version="1.0"?>?

# It is very important but not necessary. Because the statement declares the document as an XML document, which means it complies with XML syntax rules - that is it is well formed. XML protocol versioning is not a topic limited to real-time communication systems, however. Rather, it is a topic of importance to any two communicating systems that might make use of XML as the protocol signaling syntax and which may be using different versions of the protocol at any given time.

2. When do you choose element and attribute?
#XML is a markup language that is used to store data in a comprehensible manner. Making the data “comprehensible " comes about by holding the information in elements. If a piece of text is a title then it will be contained within a "title" element.If an element has no content at all, you can use a single tag finishing />
Like this:

<myEle myAttribute=”specialData”/>

Means the same as:

<myEle myAttribute=”specialData”></ myEle>
Attributes are used to indicate additional information about the element. An attribute for an element appears within the opening tag. External entity references can’t be attribute values. Internal entity references can. If there are multiple values an attribute may have, then the value of the attribute must be specified. For example, if a tag had a color attribute then the value would be: red, blue, green, etc. The syntax for including an attribute in an element is: <element attributeName="value">http://www.tizag.com/xmlTutorial/xmlelement.php

3. What is AJAX?

# AJAX is a combination of organized web development techniques used on the client-side to create interactive web applications. AJAX stands for Asynchronous JavaScript and XML. With the help of AJAX, web applications can retrieve data from the server in the background without interfering with the display of the existing page. Basically, it makes the life developer life easier. It facilitates the web application. In traditional architecture, the user must wait for the entire Web page to reload to see new results from the server in an application that requires a lot of interactivity with the business layer sitting on the server; the user must reload the entire page many times. Basically in all the web applications, the user enters the data into the form and then clicks on the submit button to submit the request to the server. Server processes the request and returns the output in new page (by reloading the whole page). This process is really inefficient, time consuming, and a little frustrating if only the small amount of data exchange is required. For example in a user registration form, this can be frustrating thing for the user, as whole page is reloaded only to check the availability of the user name. So to prevent from these drawbacks, Ajax will help in making application more interactive. With the help of Ajax, we can confirm the availability of the username without refreshing the whole page.
http://en.wikipedia.org/wiki/Ajax_(programming)