2.1 Xml - tags, elements, content, and attributes

Created using a WYSIWYG XHTML editor

I originally created the document as an XHTML document using a WYSIWYG XHTML editor that behaves muchlike a word processor. (If you don't know what WYSIWYG means, Google it.) Of course, the document has since undergone quite a lot of editing so the finalXHTML version probably doesn't match the XHTML code in Listing 3.

Transform to CNXML

Later on, I used a Java program of my own design to transform the final XHTML document into anotherflavor of XML known as CNXML for publishing on the Connexions website.

That illustrates another characteristic of XML. Because the formats of certain flavors of XML documentsare well defined, it is often practical to transform them from one flavor to another flavor.

That makes it possible for me to create the document using a program that is very similar to a word processorand then transform the output of that program into a fairly cryptic format that satisfies the publishing requirements of the website.

Your browser is rendering the document

When you accessed the document from the Connexions website, it was transformed back into an XHTML document and sent to yourcomputer.

As you can see in Listing 3, viewing raw XHTML isn't very enjoyable. Fortunately, your browser isacting as a rendering engine to render the raw XHTML text into a much more pleasing presentation format.

Back to the book example

A book that is created and maintained as an XML document could be rendered in a variety of different ways. Whichever way it is rendered, however, it wouldprobably be useful to separate and number the chapters. Therefore, the value of the number attribute could be used by the rendering engine to present the chapter number for a specific rendering.

In some renderings, the number might appear on an otherwise blank page that begins a new chapter. In a different rendering, the chapter number might appearin the upper right or left-hand corner of each page.

Tell me again, what is an element?

As I explained earlier, an element usually consists of a start tag (with optional attributes and namespace information) , an end tag , and the content sandwiched in between as shown earlier in Listing 2.

Elements can be nested

Elements can be nested inside other elements as shown in Listing 4.

In Listing 4, two chapter elements are nested inside a book element.

Why does XML use elements?

It is probably fair to say that the element constitutes the fundamental unit of information in an XML document. For example, the element defines the type ofinformation, such as chapter in our book example.

Sandwiched in between the start tag and the end tag of an element, we find the raw information (content) that the XML document is designed to convey. For a text document, you are likely to find a lot of content between the tags. Forexample, in Listing 3, there are several lines of text between the paragraph tags identified by the p and the /p enclosed in angle brackets.

Once again, what is content?

Of the four terms mentioned earlier, (tags, elements, content, and attributes) , content is the easy one. Content is sandwiched in between the start tag and the end tag of an element. Usually the content of the elements containsthe information that the XML document is designed to convey. In other words, this is where we put the information for which the document was created. Thetags and attributes are there to create the structure.

For example, if the XML document is being used for the creation and maintenance of material for a newspaper, the content constitutes the news. Ifthe XML document is being used for the creation and maintenance of a Java programming textbook, the content contains the information about Javaprogramming that we want to convey to the student.

Why do we need structure?

One of the primary objectives of XML is to separate content from presentation. If we insert the raw material as content into a structure definedby the tags, elements, and attributes, then that raw material can be presented in a variety of ways.

Miscellaneous

This section contains a variety of miscellaneous materials.

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