Creating XML Documents

HTML, about 100 elements
XML, you define your own elements
HTML Browsers try to fix bad HTML code
XML Processors do not make any guess about the structure of the document
Well-formed XML Document is the minimal requirement
Valid XML Document (DTD or XML Schema)

The World Wide Web Consortium (http://www.w3.org/)

Group of member organizations interested in the WWW
W3C is hosted at MIT
Specifications for the Web

Notes - Specification submitted by a member organization
Vector Markup Language by Microsoft
http://www.w3.org/TR/NOTE-VML
Working drafts - Specification under consideration and open to comments
XHTML 1.1 http://www.w3.org/TR/xhtml11/
Recommendations - Working drafts that the W3C has accepted.
XML 1.0 http://www.w3.org/TR/REC-xml

What is a Well-Formed XML Document?

A textual object is a well-formed XML Document if:

Taken as a whole, it matches the production labeled document
It meets all the well-formedness contraints given in this specification:
http://www.w3.org/TR/REC-xml
Each of the parsed entities which is referenced directly or indirectly whitin the document is well-formed

document ::= prolog element Misc*

Prolog:

<?xml version="1.0"?>
Comments -> 
Processing Instructions:
<?xml-stylesheet href="JavaXML.html.xsl" type="text/xsl"?> <?xml-stylesheet href="greeting.css" type="text/css"?>

Element:

Root Element contains more elements
Exactly one root element

Misc:

Comments
Processing Instructions
Whitespaces

Entity

Part of an XML Document
Hold text or binary data
May refer to other entities
Parsed entities are character data
Unparsed entities are binary data

Tags and Elements

XML Element consists of a start tag and an end tag
<document> ... </document>
Tag Names

Start with a letter <document>, an underscore <_record> or a colon (avoid using a colon)
Next characters may be letters, digits, underscore, hyphens, periods and colons (but no whitespaces)
XML Processors are case sensitive
Different tags: <document>, <DOCUMENT>, <Document>
Empty Elements have only one tag:
HTML : <img>, <li>, <hr>
XHTML : <img/>, <li/>, <hr/>

Attributes

Name-value pairs: {STATUS, "Good Credit"}
Specify additional data in start tags
<CUSTOMER STATUS="Good credit">
Attribute Names same rules as tag names
Attribute Values are strings enclosed in quotation marks

Elements vs Attributes

Too many attributes make documents hard to read
You can't specify document structure using attributes
Attributes are good for simple information

Elements vs Attributes (2)

Too many attributes make documents hard to read:

    <CUSTOMER LAST_NAME="Smith" FIRST_NAME="Sam" 
    DATE="October 15, 2001" PURCHASE="Tomatoes" 
    PRICE="$1.25" NUMBER="8" />

    <CUSTOMER>
        <NAME>
            <LAST_NAME>Smith</LAST_NAME>
            <FIRST_NAME>Sam</FIRST_NAME>
        </NAME>
        <DATE>October 15, 2001</DATE>
        <ORDERS>
            <ITEM>
                <PRODUCT>Tomatoes</PRODUCT>
                <NUMBER>8</NUMBER>
                <PRICE>$1.25</PRICE>
            </ITEM>
        </ORDERS>
    </CUSTOMER>

Elements vs Attributes (3)

Too many attributes make documents hard to read
You can't specify document structure using attributes
Attributes are good for simple information:
<BOOK ID="B1">

Building Well-Formed XML Document Structure

An XML Declaration should begin the document

<?xml version="1.0" standalone="yes"?>

Include one or more elements

<?xml version="1.0" encoding="UTF-8"?>
<DOCUMENT>
<GREETING>Hello from XML</GREETING>
<MESSAGE>Welcome to Programing XML in Java</MESSAGE>
</DOCUMENT>

Building Well-Formed XML Document Structure (2)

Include Both Start and End Tags for Elements that aren't empty: <GREETING>Hello from XML</GREETING>
Close Empty Tags with />: <SUBJECT name="XML"/>
The Root Element Must Contain All Other Elements: <DOCUMENT> ..... </DOCUMENT>

Building Well-Formed XML Document Structure (3)

Nest Elements Correctly:

<?xml version="1.0" encoding="UTF-8"?>
<DOCUMENT>
   <GREETING>Hello from XML</MESSAGE>  <--- wrong end tag
   <MESSAGE>
   Welcome to Programing XML in Java
   </GREETING> <--- wrong end tag
</DOCUMENT>

Building Well-Formed XML Document Structure (4)

Use Unique Attribute Names:

<PERSON LAST_NAME="Smith" LAST_NAME="Punin">

Use Only the Five Pre-Existing Entity References:

&amp; the & character
&lt; the < character
&gt; the > character
&apos; the ` character
&quot; the " character

Building Well-Formed XML Document Structure (5)

Surround Attribute Values with Quotes:: <IMG SRC="image.jpg"/>
Use < and & Only to Start Tags and Entities:: <TOUR CAPTION="The S&O Railway"/>