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Module 6 Study Guide and Deliverables Readings: Murach’s PHP and MySQL: Chapters 12 & 21
Assignments:
Assignment 6 Due: Thursday, February 24 at 6:00 AM ET

Term Project: Term Project Due: Monday, February 28 at 11:59 PM ET
Live Classrooms: Thursday, February 17, 6:00–8:00 PM ET
Facilitator live office: TBD

Working with AJAX, XML, and JSON

Learning Objectives

By reading the lectures and textbook, participating in the discussions, and completing the assignments, you will be able to do the following:

Utilize AJAX, XML, and JSON in web applications.
Develop programs that communicate between different systems using Web Services (including RESTful services).

Introduction

In this lecture, you will learn about XML and JSON as file formats for exchanging data between web applications. This will prepare you to use AJAX via jQuery in order to update data on a page without refreshing the entire web page. Finally we will introduce web services with a focus on SOAP and REST in order to allow web applications to talk to each other.

eXtensible Markup Language (XML) is used to define rules for encoding documents in a specified format. It is commonly used for storing and transmitting data between various systems and applications. Put another way, this means that XML can be used as a data interchange format. A data interchange format is simply a plain text data format that makes it easy to transport data between applications. It can be read by any programming language.

When we refer to XML and its usage to store information, we also want to convey that it is a specification for describing the structure of the information it is storing.

XML is a markup language just like HTML, but XML has no tags of its own. This allows you to create your own custom tags as needed for the task at hand. While you can create your own tags, you must ensure that you follow the rules of XML. Really, what XML allows you to do is define your own markup language utilizing the XML specification. Once you have created your own language based on XML, you can create XML documents using this custom language.

XML Syntax

Let’s look at an example of a XML document:

Now that you’ve seen what XML looks like, answer these questions:

What other language does this look similar to?
What is the structure of the information?
What information is being stored?
What tags were utilized?

You have probably realized that this looks similar to HTML in the way tags were used. Each student has a first and last name. It is pretty clear that we are storing information about BU students. The tags used include: , , , , and their corresponding closing tags.

Why Use XML?

As mentioned earlier, XML is used to store and transport data. It has its own tags, attributes, and values. In addition, one benefit of XML is that it very simple to extend and adapt it for your own purposes. You can create tags for your own datasets that have meaning and describe the data that is contained within the tags. Since XML is a simple text file, it is easy to share data between different systems and entities.

Other benefits of XML include:

human-readable (easy to understand)
well-structured
easy to process
easy to manipulate (for good purposes)
non-proprietary
created by W3C standards group
all standard web browsers can read XML documents, schemas, and styling
examples of real world uses include RSS and AJAX

Basic XML Rules

It is important to follow the rules of the XML specification. If your document complies with XML rules, your document will be “well-formed.”

Your document must contain a root element. It can contain only one root element. Everything must be contained within this root element with the exception of comments and processing information found in the first line of your document.
Element names must start with a letter, underscore, or colon.
Element names can contain letters, numbers, and underscores.
You cannot start the name of a tag with “xml”.
Closing tags are required.
Elements must be properly nested (first in, last out).
XML interpret tags in a case sensitive matter.
Quotation marks must be used to surround an attribute value.
White space outside of elements does not get interpreted/processed.
HTML type comments are allowed
If you want to display XML code within your XML, but not have it processed, you will want to wrap the XML code to be displayed (not parsed) with an opening tag of

Note: CDATA stands for unparsed character data. It won’t be interpreted by the XML parser.

Creating Your First XML Document

Creating a XML document is very similar to creating a HTML document. You can use a plain text editor or an IDE.

Note: Be sure to save your XML documents with the .xml file extension.

Your XML documents should contain tags that are self-explanatory, meaning that the tags should describe the content being stored within them.

The first line of your XML document is the declaration that indicates which version of XML you are using. See line 1 in the screenshot below.

The next line in the document will begin the data portion of the document, this is also known as the root element. You can only have one root element in your XML document. See line 2 below.

You will also have child elements within the root element. These child elements may in fact have their own child elements as well. Child elements are used to describe the root element. You can also add attributes to your elements that include additional information about the element, but don’t actually add to the content of the element. You can almost think of this as meta-data.

Below, you can see that is a child element of and my has the child elements of