XML is a markup language that provides a standard syntax. It is important to understand that XML specification provides only a standard syntax. Syntax can be thought of as the construct of how the information is marked up.

XML does not provide the semantics (definition) of the elements and / or attributes used within an XML vocabulary. XML allows organizations to develop their own vocabulary for their specific application.

For example, a publishing company might use an element called <title> for a title of a book, chapter, section, etc. However, legislative bodies would create an element called <title> with a complex structure for legislation.

XML can be created in many different ways. Software is required to create and process of the XML. XML is an intelligent format. XML makes it easy for computers to generate and process data. XML data is also platform independent.

The W3C XML Specification 1.0 relates only to syntax. It does not contain information about presentation, application or semantics of the XML. Other standards and specifications have been developed around the XML 1.0 specification.

It is important to understand that there are currently hundreds of XML specifications and initiatives. Some of these specifications and initiatives are currently in direct conflict with each other.

There are thousands of different applications using XML. XML standard vocabularies (DTD/Schema) have been developed for almost every industry.

All the benefits and more are available with XML that are contained on this file. It also also allows metadata (information about the information) to be included in the XML. This provides flexible indexing and retrieval, as well as a knowledge-base for information.

If you are new to the XML world or have been working with XML for only a short time, you are probably wondering why this section is included in this section. It is important that companies who develop XML applications understand the history of XML and the importance that SGML and HTML play in the world of XML.

SGML and HTML have had a profound impact on businesses and they still play and will continue to play a significant role in development of business documents. For example, a few years ago one major on-line legal publisher claimed they had more SGML information in their database than the entire WWW has in HTML. This organization continues to use SGML has a basis for their data. Organizations that are currently using SGML have continued to use their established business practices. They are using XML publishing their information on the web.

Even with the success of Panorama, SGML was complex and many people knew that it had to be simplified before it would be accepted by the world at large. XML was born by looking at SGML and deciding what was the core functionality required. This is important: XML is a subset of SGML!

Some of the functionality that was extracted from XML DTD's for simplicity purposes have been put back in W3C XML Schemas.

XML can be used to model any kind of language.

An XML document consists of the above components. An XML document must have at least one element. Everything else is optional. For example, the following tagged information would consist of a valid XML document.

<?xml version="1.0"?>
<myXML/>

Although this example isn't a realistic document, it shows how simplistic an XML document can be.

<?xml version="1.0"?>
<poem id="poem1">
	<title>The Raven</title>
	<poet>Edgar Allan Poe</poet>
	<stanza id="stanza1">
		<line>Once upon a midnight deary, while I pondered, weak and weary,</line>
		<line>Over many a quaint and curious volume of forgotten lore-</line>
		<line>While I nodded, nearly napping, suddenly there came a tapping</line>
		<line>As of some one gently rapping, rapping at my chamber door.</line>
		<line>"‘Tis some visitor," I muttered, "tapping at my chamber door-</line>
		<line>Only this and nothing more."</line>
	</stanza>
	<stanza id="stanza2">
		<line>Ah, distinctly I remember it was in the bleak December;</line>
		<line>And each separate dying ember wrought its ghost upon the floor. </line>
		<line>Eagerly I wished the morrow; - vainly I had sought to borrow </line>
		<line>From my books surcease of sorrow-sorrow for the lost Lenore-</line>
		<line>For the rare and radiant maiden whom the angels name Lenore-</line>
		<line>Nameless <whisper>here</whisper> for evermore.</line>
	</stanza>
</poem>

This slide demonstrates how information can be identified according to its content. Semantic understanding can be derived from the element names. Unique ID's can also be assigned.

Standard Generalized Markup Language - ISO 8879 (SGML) is an International Standards Organization (ISO) standard. SGML became an official ISO standard since 1986. IBM had originally created an internal IBM standard called GML (Generalized Markup Language). GML was the basis for SGML. Dr. Charles Goldfarb, one of the original architects of GML at IBM continued his work to ensure that SGML became an ISO standard. Charles Goldfarb is considered the "Father of SGML" by many.

SGML was an 'industrial strength' standard. It was complicated and was very flexible. Because of the complexity and the flexibility of the standard, vendors found it very difficult to write software to support the standard. Therefore, SGML software was and is still very expensive. However, we are seeing the costs of SGML/XML software products being driven down because of XML.

Major industries adopted SGML for their publishing standards after SGML became an ISO standard. The notable industries were:

SGML was developed to define structure and content of the information. SGML isn't concerned with the format of the information or how it is presented to potential users.

Because of the complexity and high initial cost to get into the SGML market, many organizations who were looking at the technology coined a phrase - Sounds Good, Maybe Later. Because of the high investment only large organizations with a large IT budget could use SGML. The small and medium-sized organizations only used SGML when they were forced too by larger business partners who required information in SGML. This was true for several industries, airline manufacturers, defense departments (US, UK, Australia, etc.).

The Global Hypertext Project began in December 1990 at CERN, European Laboratory for Particle Physics under the direction of Tim Berners Lee. The project needed a way to communicate between different buildings. HyperText Markup Language (HTML) was developed for this project. HTML was an application of SGML. HTML is an application that defines information based on its presentation. HTML information is not tagged according to its content or structure - however, it is still a SGML application because it has a defined DTD, elements and attributes.

HTML became the largest SGML application in the world. It became the most successful SGML application in the world. It also became the cheapest SGML application in the world. It proved that SGML could be used by the 'common man'. HTML provided the move of SGML into the mainstream of corporate computing. It was easy enough for everyone to learn. Many executives and information providers were afraid of SGML because of the learning curve and the fear of the pointy brackets. HTML was a paradigm change.

Companies and corporations flocked to HTML. However, it was soon realized by these companies that HTML was not robust enough to handle 'real business' information. SGML was still needed but SGML was still complicated. In October 1994, the second international WWW Conference in Chicago, Yuri Rubinsky, President of a small Canadian company called SoftQuad, held a session called 'SGML on the Web'. SoftQuad was (and still is) a provider of SGML/XML authoring tools. During this conference Yuri announced Panorama a browser for SGML. Panorama proved that you could provide real SGML on the Web.

Many companies who were doing SGML flocked to Panorama. One major telecommunications company bought 30,000 copies of Panorama to put on all their employees desktop for access to corporate data. The U.S. Office of the Secretary of Defense used Panorama to access administrative data.

HTML is an SGML vocabulary. HTML broke the SGML edict that SGML is about structure content and not about format. HTML tags were all about formatting. However, HTML proved to the world that you could do SGML in a cost effective environment. Cheap tools for creating HTML flooded the marketplace very quickly.

HTML has fixed formatting tags. You cannot use content tags to provide meaning to the HTML element. Some companies have tried to include semantic meaning for the elements by using the 'class' attributes.

There is no modularity or reusability to HTML. You can do 'server-side' includes with HTML but this is hardware / software specific.

You cannot establish relationship within HTML using the hierarchy (parent/child structure). There are basically only two structures to an HTML document, <head> and <body>.

<HTML>
	<HEAD>
		<TITLE>The Raven</TITLE>
	</HEAD>
	<BODY>
		<H1 ALIGN="CENTER">The Raven</H1>
		<H2 ALIGN="CENTER"> Edgar Allan Poe</H2>
                <HR>
		<P>Once upon a midnight deary, while I pondered, weak and weary,<BR>
	   	   Over many a quaint and curious volume of forgotten lore-<BR>
	   	   While I nodded, nearly napping, suddenly there came a tapping<BR>
	   	   As of some one gently rapping, rapping at my chamber door.<BR>
	   	   "‘Tis some visitor," I muttered, "tapping at my chamber door-<BR>
	   	   Only this and nothing more.
        		</P>
		<P>Ah, distinctly I remember it was in the bleak December;<BR>
	   	   And each separate dying ember wrought its ghost upon the floor. <BR>
	   	   Eagerly I wished the morrow; - vainly I had sought to borrow <BR>
	   	   From my books surcease of sorrow-sorrow for the lost Lenore-<BR>
	   	   For the rare and radiant maiden whom the angels name Lenore-<BR>
	   	   Nameless <FONT color="red">here</FONT> for evermore.
		</P>
	</BODY>
</HTML>

Looking at the poem above tagged in HTML, you can see that you cannot identify pieces of the poem. For example, you can't recognize the name of the poem, the author or the individual stanza's.

The lack of robust tagging limits the usability of the information. For example, with the poem tagged as HTML, you can't ask for the author of the poem 'The Raven'. You would have to do a full-text search for 'The Raven' then take your chances that you find the poem 'The Raven' and not some other reference to 'the raven'.

XML 1.0 provides most of the advantages of SGML without the complexity.

It is important to distinguish the difference between all the specifications around XML and XML 1.0. The surrounding specifications, XML Schema, RDF, XSL(T), can be difficult to understand. However, the core XML is very easy.

It doesn't take the large cost investment to use XML that it did with SGML. A lot of good XML tools are open source. It is inexpensive to create and present XML information. There are many times more tools available for XML than there were for SGML. SGML tools were very limited.

As noted before, the activities currently around XML are difficult to navigate. It is important that managers and developers understand the implications of any XML development before trudging ahead.

In some cases, the specification that is used for a particular project, i.e., SOAP/ebXML TRP, Schema(s)/DTD, may depend on the software that will be used to implement the XML project.

A good example would be an authoring tool. Currently, authoring tools (Arbortext Epic, WordPerfect, Frame +SGML) do not support schemas. Corel's XMetaL 3.0 currently supports W3C Schema language. Epic editor is rumored to support schemas during a future release.

HTML

Figure 1. Hierarchical Diagram of HTML DTD

XML - Structure and Content Driven

Figure 2. Hierarchical Diagram of a Coffee Order DTD

Comparing the two hierarchical graphics above, you can see that HTML has two levels of hierarchy, <head> and <body> The <body> can contain any element in any order.

The <CoffeeOrder> element shows that you can order multiple types of <Latte>, <Mocha> or <Cappuchino> . You can also see that the model is extensible if the menu grows, for example if they decide to include an <ExtraGrande> size.

A well-formed document requires that all elements must have a start tag and an end tag. It also requires each attribute value to be delimited in quotes (double or single are fine as long as they are consistent).

If you are familiar with HTML authoring, this is different. In HTML, you can have a start tag with an ending tag. Each attribute has to be enclosed in quotes.

<H1 align=center>HTML snippet</h1>
<hr>
<p>This is a paragraph
<p>Next paragraph

Below is the resulting well-formed document fragment.

<h1 align="center">HTML snippet</h1>
<hr/>
<p>This is a paragraph</p>
<p>Next paragraph</p>

Although it is good form to enclose attribute values in quotes in attribute values, HTML browsers are lenient in this respect.

Figure 5. XML Document

A complete XML document is comprised of three components. The DTD or Schema is used to create a rule-based document. It also is used to validate the document to ensure that has been created based upon the defined rules.

The stylesheet is used to present the document in a human-readable format. A browser or publishing engine uses the stylesheet to represent the document visually.

http://www.w3.org/TR/NOTE-sgml-xml.html 

<?xml version="1.0"?>

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>

The version number is the only required component of the XML declaration. Currently the version is 1.0.

The encoding declaration describes what character encoding is used.

The standalone declaration declares what components of the document type definition are necessary for complete processing.

An attribute is a property that is associated to an element.

XML provides the powerful capability of reusing information objects. An information object is a logical piece of information. A good example of an information object is an address. An individual address can be used in many different contexts within a single document, transaction or message. For instance, the same address could be reused within a purchase order for requestor, shipping address, etc. This address can also be used in multiple transactions. XML provides the facility for these reusable objects. Create once - reuse many.

Figure 9. Reusable Object

The graphic above, shows how an information object can be reused. For example, the poem "The Raven" by Edgar Allen Poe can be used in multiple locations, one chapter devoted to Edgar Allen Poe and another in a chapter concerning birds in poetry. This becomes really useful for on-line information. Everywhere that the poem "The Raven" could be referenced you would have only one source of the document.

Figure 10. Information Objects

This graphic shows how the information objects for purchaser can be used in both an invoice and a purchase order. It also shows how the catalog item can be used in the catalog, invoice and purchase order. In the following slides we will show how the information objects remain the same, even though the objects are processed differently depending on the particular document model (invoice, purchaser and catalog item).

Figure 11. Example of a Common Business Object

The above model shows how a common information object can be created for a standard structure. This model can be used in multiple contexts, as well as multiple documents.

An example of a common information object would be a table. There are currently two table models in wide use. The first and oldest model is the CALS (Computer Aided Logistics Support) table model. The second is the HTML table model. The CALS table model is the more robust of the two. However, both table models have been widely used in XML applications. In some cases, the table models have been enhanced to allow for individualized tables, i.e., source notes, etc.

Figure 12. Common Business Object Is Reusable

The graphic above shows how the information object <item> can be enhanced for the purchase order and invoice applications by wrapping the <item> element in a parent element and adding the <qty> element before the item and the <amount> after the item. This way, an external program can be used to calculate the <amount> element once the <qty> ordered is known.

Presentation standards have been developed for presenting XML. This provides the ability to create one stylesheet and present it across all platforms. There are currently two stylesheet specifications that can be used with XML (CSS and XSL/XSLT).

Link to Coffee Example.

<!DOCTYPE CoffeeOrder SYSTEM "coffee.dtd">
			 <CoffeeOrder> 
         <Type> 
            <Name> <Latte/> </Name>
			         <Size> <Grande/> </Size> 
            <Cost>$3.40</Cost>
			     </Type> 
        <Type> 
             <Name> <Mocha/> </Name>
			          <Size> <Vente/> </Size> 
            <Cost>$4.40</Cost>
			     </Type> 
        <Type> 
             <Name> <Cappuchino/> </Name>
			          <Size> <Tall/> </Size> 
             <Cost>$2.40</Cost>
			     </Type> 
   </CoffeeOrder> 

Presentation of the XML is based on the tag elements. If you look at the tagged example, you will see that there is no form elements used, there isn't any presentation information included in the text. However, showing the example shows a nice presentation order form based on the XML elements. The presentation can also be attached to attributes as well.

P { 
   font-family: non-serif; 
   font-size: medium; 
   color: black;
			overflow: visible; 
   margin-left: 40px; 
   margin-right: 40px 
} 

CSS stylesheets can be used with HTML and XML. CSS can also be used to enhance HTML presentation with XSLT transformations to HTML.

<xsl:template match="CoffeeOrder">   <html>
			  <head> 
        <title>Cool Coffee Menu </title> 
     </head>
			  <body font-family="Arial, helvetica, sans-serif" 
           font-size="10pt" bgcolor="#EEEEEE"> 
        <h1 align="center">Cool Coffee Menu</h1>
			     <hr width="75%"/> 
        <form method="POST">  
        <center>
        <table border="1" cellpadding="10"> 
           <tr> 
              <th colspan="8" align="center">Place Your Order</th>
           </tr>
			           <xsl:apply-templates/> 
        </table> 
        </center> 
        <p align="center">
            <a href="order.xml">Place and Order</a>
        </p>
			     </form> 
     </body> 
   </html> 
</xsl:template> 

XSLT defines how to transform XML documents into other XML documents or into HTML or text documents. The XSLT specification defines how to filter, sort and transform an XML information which allows presentation to be applied to the transformed document.

 <xsl:template match="para"> 
    <fo:block
			    font-family="Times" 
       font-size="11pt" 
       margin-left="25pt" 
       margin-right="25pt"
			    space-before.minimum="18pt"> 
       <xsl:apply-templates/> 
    </fo:block>
</xsl:template> 

XSL-FO is the style component of the XSL specification. The XSL-FO specification provides the mechanism to support complex page layout, similar to desktop publishing capability. It uses CSS as a basis for the style attributes. It also used XSLT as the mechanism to transform an XML document into an XSL-FO document.

If you are reading these instructor notes, the printed copies have been created using XSL-FO for formatting.

<?xml-stylesheet href="poem.xsl" type="text/xsl"?>
<?xml-stylesheet href="poem.css" type="text/css"?>

You can attach the stylesheet to an XML document using a processing instruction. Currently there isn't a definitive standard for attaching stylesheets. However, browsers recognize this mechanism.