xml for beginners ebook

XML for beginnerseXtensible Markup Language... HTML• HTML is a HyperText Markup language – Designed for a specific application, namely, presenting and linking hypertext... Main Features

XML for beginners

eXtensible Markup Language

Introduction and Motivation

Dr Praveen Madiraju Modified from Dr.Sagiv’s slides

XML vs HTML

• HTML is a HyperText Markup language

– Designed for a specific application, namely, presenting and linking hypertext

Main Features of XML

• No fixed set of tags

– New tags can be added for new

applications

• An agreed upon set of tags can be used

in many applications

– Namespaces facilitate uniform and

coherent descriptions of data

• For example, a namespace for address books determines whether to use <tel> or <phone>

Main Features of XML (cont’d)

• XML has the concept of a schema

– DTD and the more expressive XML

Schema

• XML is a data model

– Similar to the semistructured data model

• XML supports internationalization (

Unicode ) and platform independence

(an XML file is just a character file)

XML is the Standard for

XML is not Alone

• XML Schemas strengthen the data-modeling capabilities of XML (in comparison to XML with only DTDs)

• XPath is a language for accessing parts of

XML documents

• XLink and XPointer support cross-references

• XSLT is a language for transforming XML

documents into other XML documents

(including XHTML, for displaying XML files)

– Limited styling of XML can be done with CSS alone

• XQuery is a lanaguage for querying XML

documents

The Two Facets of XML

• Some XML files are just text documents with tags that denote their structure and include

some metadata (e.g., an attribute that gives the name of the person who did the

proofreading)

– See an example on the next slide

– XML is a subset of SGML (Standard Generalized

Markup Language)

• Other XML documents are similar to

database files (e.g., an address book)

XML can Describe the Structure of a Document

XML Syntax

W3Schools Resources on XML Syntax

The Structure of XML

• XML consists of tags and text

• Tags come in pairs <date> </date>

– good

<date> <day> </day> </date>

– bad

<date> <day> </date> </day>

(You can’t do <i> <b> </i> </b> in HTML)

<name> Lisa Simpson </name>

<mother idref = “marge”/>

<father idref = “homer”/>

of a name and

a value

XML Text

XML has only one “basic” type – text

It is bounded by tags, e.g.,

<title> The Big Sleep </title>

<year> 1935 </ year> – 1935 is still text

• XML text is called PCDATA

– (for parsed character data)

• It uses a 16-bit encoding, e.g., \&\#x0152 for

XML Structure

• Nesting tags can be used to express

various structures, e.g., a tuple

XML Structure (cont’d)

• We can represent a list by using the

same tag repeatedly:

The segment of an XML document

between an opening and a corresponding closing tag is called an element

The Header Tag

• <?xml version= "1.0" standalone= "yes/no"

Processing Instructions

<?xml version="1.0"?>

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

<!DOCTYPE doc SYSTEM "doc.dtd">

<doc>Hello, world!<! Comment 1 ></doc>

<?pi-without-data?>

<! Comment 2 >

<! Comment 3 >

Enter the member by the name on his or her papers Use the

NAME tag The NAME tag has two attributes Common (all in

lowercase, please!) is the dog's call name Breed (also in all

lowercase) is the dog's breed Please see the breed reference

guide for acceptable breeds Your entry should look something

like this:

</ DESCRIPTION >

< EXAMPLE >

<![CDATA[ <NAME common="freddy"

breed"=springer-spaniel">Sir Fredrick of Ledyard's End</NAME> ]]>

We want to see the text as is, even though

it includes tags

A Complete XML Documenthttp://www.mscs.mu.edu/~praveen/Teachi ng/fa05/AdvDb/Lectures/bib.xml

Well-Formed XML Documents

• An XML document (with or without a DTD) is

well-formed if

– Tags are syntactically correct

– Every tag has an end tag

– Tags are properly nested

– There is a root tag

– A start tag does not have two occurrences of the same attribute

An XML document must be well formed