Myers

What’s wrong with HTML? XML

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C.R. Myers, Assistant Professor School of Printing Management & Sciences Rochester Institute of Technology

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Simple, but not powerful Tags pre-defined Not strict about syntax Tags are formatting oriented

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What XML is NOT

XML– eXtensible Markup Language ◆ ◆ ◆ ◆ ◆

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Open standard Any kind of data Unicode character set Clear syntax Unambiguous structure

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A A A A

replacement for HTML programming language network transport protocol database

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XML ◆ ◆

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A sample XML file Doc. Proc. Lang. 2081-742 C.R. Myers Tuesday, Noon - 2PM Thursday, Noon - 2PM

A language for creating markup languages Resembles HTML or SGML ◆ Tags, attributes and values ◆ DTD's Portable data

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Conceptual structure

XML entities ◆

Course

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Name

Number

Instructor

Time

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Time

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less than = < (<) greater than = > (>) quotation mark = " (") apostrophe = ' (') ampersand = & (&)

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XML syntax rules ◆ ◆ ◆ ◆ ◆ ◆

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Tags are case-sensitive is different from

Tags are case sensitive Each document must have a root Closing tags are required Values must be enclosed in quotation marks Elements must be properly nested Entities must be declared

This is bad XML

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XML documents must have a root

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Closing tags are required



This is bad XML

This is also bad


<subchild>

This is ok

This is the shortcut for an empty tag


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Values must be in quotation marks

Elements must be properly nested

<student id=1234>Bad Student!

Badly nested!

<student id="1234">Good Student

Looks good!

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Attributes vs. Elements

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Attributes vs. Elements

Using an Element for gender:

Using an Attribute for gender:





female

Jane

Jane

Doe

Doe





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Attribute disadvantages

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Attributes still useful

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Can't contain multiple values

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Not very expandable

<messages>

Great for internal info, not needed by the user

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Can't describe structures

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More difficult to manipulate

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Hard to test against a DTD

<note id="123">Blah, blah, blah. <note id="124">More boring stuff

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Types of XML documents

"Well-formed" XML Follows the XML syntax rules

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Well-formed

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Valid

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Invalid

Document Processing Languages 2081-742 CIAS 4 <desc>Grad publishing technology

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"Valid" XML ◆

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Imbedded DTD

A well-formed XML doc that conforms to a DTD


Document Processing Languages 2081-742 CIAS 4 <desc>Grad publishing technology

definitions go here ]>

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External DTD

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Parts of a DTD



Elements Attributes Entities PCDATA CDATA

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Declaring Elements in a DTD

Declaring Elements in a DTD (cont’d) Creates an element which can contain both plain text and tags Creates an element which can contain plain text but NOT other tags Creates an empty element

General Form: element-name is the name of the tag you are defining element-rule determines what content is legal in the tag

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Declaring Elements in a DTD (cont’d)

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Declaring Elements in a DTD (cont’d)

Creates an element with children which must be present in the order listed Creates an element with options. Either child1 or child2 must appear, but not both.

Creates an element with a child which must appear zero or one times Creates an element with a child which must appear one or more times Creates an element with a child which may appear zero or more times

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Declaring Attributes in a DTD

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Possible values for default

General form:

#REQUIRED means that the value must be specified #IMPLIED means that the value is optional

target-element is the element to which the attribute applies name is the attribute name type is what type of data the attribute contains default is whether the item is required 29

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Legal types

An XML Example

CDATA Character data

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We will define a person like this:

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A person is required to be either male or female A person has a name which consists of: ◆ A first name ◆ A last name ◆ One (optional) nickname A person has an occupation A person has a description

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A list of values e.g. for marital status (single | married | divorced | widowed)

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An XML Example ◆

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The “person” DTD

We will define a person like this:



Charles Myers C.R.

college professor <description>bald geek

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What's wrong with DTD's ◆ ◆

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XML Schema

DTD’s use old SGML style definitions DTD are not written in XML

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XML definition system developed to replace Document Type Definitions

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Other related technologies ◆ ◆ ◆ ◆ ◆ ◆

Transforming XML

CSS - Cascading Style Sheets for display XSL - Extensible Stylesheet Language for display XSLT - XSL Transformations Xpath - Allows XML files to include other content Xlink - Allows XML files to link to other XML files Xquery - Allows XML files to query databases

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XSLT ◆ Extensible Stylesheet Language - Transformations ◆ Can convert XML to other languages ◆ ◆ ◆ ◆ ◆

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SGML HTML PDF PostScript Just about anything else

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