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Beyond HTML: XML. ISC325. The Limits of HTML. HTML was designed for formatting text on a Web page.

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the limits of html
The Limits of HTML
  • HTML was designed for formatting text on a Web page.
  • Because HTML is not extensible, it cannot be modified to meet specific needs. Browser developers have added features making HTML more robust, but this has resulted in a confusing mix of different HTML standards.
  • HTML cannot be applied consistently. Different browsers require different standards making the final document appear differently on one browser compared with another.
introducing xml
Introducing XML
  • XML (Extensible Markup Language)
    • used to design markup languages
  • XML documents must be evaluated with an XML parser.
  • An XML document with correct syntax is a well-formed document.
  • A well-formed document with correct content and structure is a valid document.
  • DTD specifies correct content and structure.
xml parsers
XML Parsers
  • An XML processor (also called XML parser) evaluates the document to make sure it conforms to all XML specifications for structure and syntax.
  • XML parsers are strict. It is this rigidity built into XML that ensures XML code accepted by the parser will work the same everywhere.
    • Microsoft’s parser is called MSXML and is built directly in IE versions 5.0 and above.
    • Netscape developed its own parser, called Mozilla, which is built into version 6.0 and above.
well formed and valid xml documents
Well-Formed and Valid XML Documents
  • There are two categories of XML documents
    • Well-formed
    • Valid
  • An XML document is well-formed if it contains no syntax errors and fulfills all of the specifications for XML code as defined by the W3C.
  • An XML document is valid if it is well-formed and also satisfies the rules laid out in the DTD or schema attached to the document.
the document creation process
The Document Creation Process

This figure shows the document creation process

the structure of an xml document
The Structure of an XML Document
  • XML documents consist of three parts
    • The prolog
    • The document body
    • The epilog
  • The prolog is optional and provides information about the document itself
  • The document body contains the document’s content in a hierarchical tree structure.
  • The epilog is also optional and contains any final comments or processing instructions.
the structure of an xml document the xml declaration
The Structure of an XML Document: The XML Declaration
  • The XML declaration is always the first line of code in an XML document. It tells the processor what follows is written using XML. It can also provide any information about how the parser should interpret the code.
  • The complete syntax is:

<?xml version=“version number” encoding=“encoding type” standalone=“yes | no” ?>

  • A sample declaration might look like this:

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

the structure of an xml document inserting comments
The Structure of an XML Document: Inserting Comments
  • Comments or miscellaneous statements go after the declaration. Comments may appear anywhere after the declaration.
  • The syntax for comments is:

<!- - comment text- ->

  • This is the same syntax for HTML comments
elements and attributes
Elements and Attributes
  • Elements are the basic building blocks of XML files.
  • An open or empty element: contains no content

<element_name/>

  • A closed element, has the following syntax:

<element _ name>Content</element _ name>

  • Example:

<Artist>Miles Davis</Artist>

elements and attributes11
Elements and Attributes
  • Element names are case sensitive
  • Elements can be nested, as follows:

<CD>Kind of Blue

<TRACK>So What (3:22)</TRACK>

<TRACK>Blue in Green (5:37)</TRACK>

</CD>

elements and attributes12
Elements and Attributes
  • XML Elements are extensible and they have relationships.
  • Elements are related as parents and children.
  • All elements must be nested within a single document or root element. There can be only one root element.
elements and attributes13
Elements and Attributes
  • XML elements can have attributes.
  • Attributes often provide information that is not a part of the data. In the example below, the file type is irrelevant to the data, but important to the software that wants to manipulate the element:

<file type="gif">computer.gif</file>

  • . Attributes are text strings and must be placed in single or double quotes. The syntax is:

<element_name attribute=“value”> … </element_name>

elements and attributes14
Elements and Attributes

{

prolog

document elements

character references
Character References
  • Special characters, such as the symbol for the British pound, can be inserted into your XML document by using a character reference. The syntax is:

&#character;

character references16
Character References
  • Character is a entity reference number or name from the ISO/IEC character set.
  • Character references in XML are the same as in HTML.
character references17
Character References

This figure shows commonly used character reference numbers

character references18
Character References

character reference

displaying an xml document in a web browser
Displaying an XML Document in a Web Browser
  • XML documents can be opened in Internet Explorer or in Netscape Navigator.
  • If there are no syntax errors. IE will display the document’s contents in an expandable/collapsible outline format including all markup tags.
  • Netscape 7.1 will display like IE does.
  • Netscape 6.2 will display the contents but neither the tags nor the nested elements.
linking to a style sheet
Linking to a Style Sheet
  • The easiest way to turn an XML document into a formatted document is to link the document to a style sheet.
  • The XML document and the style sheet are combined by the XML processor to display a single formatted document.
linking to a style sheet23
Linking to a Style Sheet

There are two main style sheet languages used with XML:

    • Cascading Style Sheets (CSS) and Extensible Style Sheets (XSL)
  • CSS is supported by most browsers and is relatively easy to learn and use.
  • XSL is more powerful, but not as easy to use as CSS.
linking to a style sheet24
Linking to a Style Sheet
  • There are some important benefits to using style sheets:
    • By separating content from format, you can concentrate on the appearance of the document
    • Different style sheets can be applied to the same XML document
    • Any style sheet changes will be automatically reflected in any Web page based upon the style sheet
applying a style to an element
Applying a Style to an Element
  • To apply a style sheet to a document, use the following syntax:

selector {attribute1:value1; attribute2:value2; …}

  • selector is an element (or set of elements) from the XML document.
  • attribute and value are the style attributes and attribute values to be applied to the document.
applying a style to an element26
Applying a Style to an Element
  • For example:

ARTIST {color:red; font-weight:bold}

  • will display the text of the ARTIST element in a red boldface type.
creating processing instructions
Creating Processing Instructions
  • The link from the XML document to a style sheet is created using a processing statement.
  • A processing instruction is a command that gives instructions to the XML parser.
creating processing instructions28
Creating Processing Instructions
  • For example:

<?xml-stylesheet type=“style” href=“sheet” ?>

  • Style is the type of style sheet to access and sheet is the name and location of the style sheet.
style sheet
Style Sheet

This figure shows the cascading style sheet stored in the JW.css file

linking to the jw css style sheet
Linking to the JW.css Style Sheet

This figure shows how to link the JW.css style sheet to the Jazz.xml file

processing instruction to access the JW.css style sheet

xml dtd
XML DTD
  • Document Type Definition or Schema
  • Defines rules for how data in the document should be structured.
  • Force a document to follow a defined structure
  • A DTD can be declared inline in your XML document, or as an external reference.
internal doctype declaration
Internal DOCTYPE declaration

Root element

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

<!DOCTYPE SPECIALS [

<!ELEMENT SPECIALS (TITLE,CD)>

<!ELEMENT TITLE (#PCDATA)>

<!ELEMENT CD (ARTIST, TRACK)>

<!ELEMENT CD (#PCDATA)>

<!ELEMENT ARTIST (#PCDATA)>

<!ELEMENT TRACK (#PCDATA)>

]>

<SPECIALS>

<TITLE>MOnthly Specials at the Jazz Warehouse</TITLE>

<CD>Kind of Blue

DATA statements

external doctype declaration

<?xml version="1.0"?>

<!DOCTYPE SPECIAL SYSTEM “special.dtd">

External DOCTYPE declaration

<SPECIALS>

<TITLE>Monthly Specials at the Jazz Warehouse</TITLE>

<CD>Kind of Blue

<ARTIST>Miles Davis</ARTIST>

<TRACK length="9:22">So what</TRACK>

<TRACK length="9:46">Freddie Freeloader</TRACK>

<TRACK length="5:37">Blue in Green</TRACK>

<TRACK length="11:33">All Blues</TRACK>

a copy of the file speical dtd containing the dtd

<!ELEMENT SPECIALS (TITLE,CD)>

<!ELEMENT TITLE (#PCDATA)>

<!ELEMENT CD (ARTIST, TRACK)>

<!ELEMENT CD (#PCDATA)>

<!ELEMENT ARTIST (#PCDATA)>

<!ELEMENT TRACK (#PCDATA

a copy of the file “speical.dtd" containing the DTD:
slide36

XML document 1

DTD

external subset

DTD internal subset

XML document 3

XML document 2

DTD internal subset

DTD internal subset

creating an xml document xml syntax
Creating an XML document(XML Syntax)
  • XML document must be well formed:
    • A root element is required.
    • Closing tags are required.
    • Elements must be properly nested.
    • Case matters.
    • Attribute values must be quoted.
    • Entity references must be declared in a DTD or a schema.
what s wrong
What’s Wrong

<?xml version=“1.0” ?>

<CD>Kind of Blue

<TRACK>So What (9:22)</TRACK>

<TRACK>Freddie Freeloader (9:46)</TRACK>

<TRACK>All Blues (11:33)</TRACK>

<TRACK>Flamenco Sketches (9:26)</TRACK>

</CD>

<CD>Cookin’

<TRACK>My Funny Valentine (5:57) </TRACK>

<TRACK> Blues by Five (9:53) </TRACK>

<TRACK> Airegin (4:22) </TRACK>

</CD>

slide39

Parsed character data (PCDATA) is text parsed by a browser or parser.

  • Unparsed character data (CDATA) is text not processed by the browser or parser.
cdata sections
CDATA Sections
  • A CDATA section is a large block of text the XML processor will interpret only as text.
  • The syntax to create a CDATA section is:

<! [CDATA [

Text Block

] ]>

cdata sections41
CDATA Sections
  • In this example, a CDATA section stores several HTML tags within an element named HTMLCODE:

<HTMLCODE>

<![CDATA[

<h1>The Jazz Warehouse</h1>

<h2>Your Online Store for Jazz Music</h2>

] ]>

</HTMLCODE>

cdata sections42
CDATA Sections

This figure shows the revised Jazz.xml file

CDATA section

displaying an xml document in a web browser43
Displaying an XML Document in a Web Browser
  • To display the Jazz.xml file in a Web browser:

1. Start the browser and open the Jazz.xml file located in the Tutorial.01/Tutorial folder of your Data Disk.

2. Click the minus (-) symbols.

3. Click the resulting plus (+) symbols.

displaying an xml document in a web browser44
Displaying an XML Document in a Web Browser

This figure shows the revised Jazz.XML file as seen in Internet Explorer 6.0 and Netscape 6.2