XML_1.ppt

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Service-Oriented Computing

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What is Markup(encoding)?



Markup is text that is added to the data of a document in

order to convey information about it.

.



The markup instructions are often called

"tags."

 Example:

<centre on> This is a <italics on> very serious <italics off> matter.<centre off>

This is a

very

serious

matter.

 _{Historically, the word}_markup_{has been used to describe annotation}

within a text intended to instruct a typist how a particular passage should be printed or laid out.

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What is XML?



XML stands for

eXtensible Markup Language



XML is a markup language for documents containing

structured information



XML is used for describing other languages(i.e WSDL,RDF,

WML)



XML is used for data interchange



XML DTD and XML Schema define rules to describe data



An open W3C standard



A subset of SGML

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What is XML?



XML is a “use everywhere” data specification

Documents Configuration

Database Application X

Repository

XML XML

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Documents vs. Data



XML is used to represent two main types of things:

– Documents

 _{Lots of text with tags to identify and annotate portions}

of the document

– Data

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XML and Structured Data



Pre-XML representation of data:



XML representation of the same data:

“PO-1234”,”CUST001”,”X9876”,”5”,”14.98”

<PURCHASE_ORDER>

<PO_NUM> PO-1234 </PO_NUM> <CUST_ID> CUST001 </CUST_ID> <ITEM_NUM> X9876 </ITEM_NUM> <QUANTITY> 5 </QUANTITY>

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Benefits of XML



Open W3C standard



Representation of data across heterogeneous

environments

– Cross platform

– Allows for high degree of interoperability



Strict rules

– Syntax

– Structure

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9

HTML and XML

XML is not a replacement for HTML.

HTML XML

HTML was designed to display data, with focus on how data looks

XML was designed to transport and store data, with focus on what data is

HTML is used to mark up text so it can be displayed to users

XML is used to mark up data so it can be processed by computers

HTML describes both structure (e.g. , <h2>, ) and appearance (e.g. , , )

XML describes only content, or “meaning”

HTML uses a fixed, unchangeable set of tags

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10

HTML and XML



HTML and XML look similar, because they are both

SGML

languages (SGML =

Standard Generalized

Markup Language

)

– Both HTML and XML use

elements

enclosed in

)

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11

HTML and XML



HTML is for humans

– HTML describes web pages

– You don’t want to see error messages about the web pages you visit

– Browsers ignore and/or correct as many HTML errors as they can, so HTML is often sloppy



XML is for computers

– XML describes data

– The rules are strict and errors are not allowed  In this way, XML is like a programming language

– Current versions of most browsers can display XML  However, browser support of XML is spotty at best

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12

HTML vs. XML

<h1> Bibliography </h1>

 Foundations of DBs, Abiteboul, Hull, Vianu  Addison-Wesley, 1995

 Logics for DBs and ISs , Chomicki, Saake, eds.

 Kluwer, 1998

<bibliography>

<book> <title> Foundations of DBs </title> <author> Abiteboul </author> <author> Hull </author>

<author> Vianu </author>

<publisher> Addison-Wesley </publisher> ....

.</book>

<book> ... <editor> Chomicki </editor>... </book> ... </bibliography>

HTML tags:

presentation, generic document structure

XML tags:

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13

XML-related technologies

 DTD (Document Type Definition) and XML Schema are used to define legal XML tags and their attributes for particular purposes

 CSS (Cascading Style Sheets) describe how to display HTML or XML in a browser

 _{XSLT (eXtensible Stylesheet Language Transformations)} _and XPath are used to translate from one form of XML to another

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Layout of a typical XML document

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Components of an XML Document



Processing instructions(prologue)

– Encoding specification (Unicode by default) – Namespace declaration

– Schema declaration



Elements

– Each element has a beginning and ending tag

 <TAG_NAME>...</TAG_NAME>

– Elements can be empty (<TAG_NAME />)



Attributes

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The Prolog (processing instructions)/XML declaration

 It tells the browser or parser that this document is marked up in XML. This prolog is actually a part of HTML as well, but most HTML authors leave it out. In HTML the prolog might look like this:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">

This tells browser that this document will be using HTML 4.0 Transitional.

 _{But the prolog for an XML document can also contain:} – the DTD or schema being used

– declarations of special pieces of text – text encoding

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17

The Prolog (processing instructions)/XML declaration



The XML declaration statement is used to indicate that the

specified document is an XML document.



The XML declaration looks like this:

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

 The XML declaration is not required by browsers, but is required by most XML processors (so include it!)

 XML declaration starts with <? xml, and ends with ?>  version="1.0" is required (this is the only version so far)

 encoding can be "UTF-8" (ASCII) or "UTF-16" (Unicode), or something else, or it can be omitted

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18

Elements and attributes



An XML element is the basic syntactic construct of an XML

document



Attributes and elements are somewhat interchangeable



Example using just elements:

<name>

<first>David</first> <last>Matuszek</last> </name>



Example using attributes:

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19

Entities



Five special characters must be written as entities:

& for & (almost always necessary)

< for < (almost always necessary) > for > (not usually necessary)

" for " (necessary inside double quotes) ' for ' (necessary inside single quotes)



These entities can be used even in places where they

are not absolutely required

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20

CDATA



By default, all text inside an XML document is parsed.



The term CDATA is used about text data that should not be

parsed by the XML parser.



You can force text to be treated as unparsed

character data

by

enclosing it in

<![CDATA[ ... ]]>



Any characters, even

&

and

<

, can occur inside a CDATA



Whitespace inside a CDATA is (usually) preserved



CDATA is useful when your text has a lot of illegal characters

(for example, if your XML document contains some HTML text)

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CDATA Example

 Some text, like JavaScript code, contains a lot of "<" or "&" characters. To avoid errors script code can be defined as CDATA.

 A CDATA section starts with "<![CDATA[" and ends with "]]>":

<script> <![CDATA[

function matchwo(a,b) {

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22

Comments





Comments are useful for:

– Explaining the structure of an XML document

– Commenting out parts of the XML during development and testing



Comments are not elements and do not have an end tag



The blanks after

<!--

and before

-->

are optional



The character sequence

--

cannot occur in the comment



The closing bracket must be

-->

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Well-formed vs. Valid



XML must be

well-formed

(An XML document that obeys the syntax rules is said to be well-formed)

– correct syntax

– tags match, tags nest, all characters legal

– parser must reject if not well-formed



XML may be

valid

with respect to a Schema (A well-formed

XML document that conforms to its schema is said to be valid.)

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24

Rules for Well-formed XML (XML Syntax))



Every XML document must have one and only one root element



Every element must have both a start tag and an end tag, e.g.

– But empty elements can be abbreviated: <break />.

– XML tags may not begin with the letters xml, in any combination of cases



Elements must be properly nested,

e.g. not

bold and italic



Attribute values must be enclosed in “” or ‘’



Processing instructions are optional



XML is case-sensitive

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Namespaces: Overview

 An XML namespace is a collection of names, identified by a URI reference, which are used in XML documents as element types and attribute names.



Allow authors to differentiate between tags of the same

name (using a prefix)

– Frees author to focus on the data and decide how to best describe it – Allows multiple XML documents from multiple authors to be merged



Identified by a URI (Uniform Resource Identifier)

– When a URL is used, it does NOT have to represent a live server – To guarantee uniqueness, typically a URI (Uniform Resource

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Namespaces: Declaration

xmlns: bk = “urn:mybookstuff.org:bookinfo”

Namespace declaration examples:

Namespace declaration Prefix URI (URL)

xmlns: bk = “http://www.example.com/bookinfo/”



There are two ways to use namespaces:

– Declare a default namespace

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Namespaces: Examples

<BOOK xmlns:bk=“http://www.bookstuff.org/bookinfo”> <bk:TITLE>All About XML</bk:TITLE>

<bk:AUTHOR>Joe Developer</bk:AUTHOR>

<bk:PRICE currency=‘US Dollar’>19.99</bk:PRICE>

<bk:BOOK xmlns:bk=“http://www.bookstuff.org/bookinfo” xmlns:money=“urn:finance:money”>

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Namespaces: Default Namespace



An XML namespace declared without a prefix becomes

the default namespace for all sub-elements



All elements without a prefix will belong to the default

namespace:

<BOOK xmlns=“http://www.bookstuff.org/bookinfo”> <TITLE>All About XML</TITLE>

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Namespaces: Scope



Unqualified elements belong to the inner-most default

namespace.

– BOOK, TITLE, and AUTHOR belong to the default book namespace

– PUBLISHER and NAME belong to the default publisher namespace

<BOOK xmlns=“www.bookstuff.org/bookinfo”> <TITLE>All About XML</TITLE>

<AUTHOR>Joe Developer</AUTHOR>

<PUBLISHER xmlns=“urn:publishers:publinfo”> <NAME>Microsoft Press</NAME>

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Namespaces: Attributes



Unqualified attributes do NOT belong to any namespace

– Even if there is a default namespace

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Valid XML



XML is

valid

if it declares a DTD/XSD Schema and

conforms to that schema



Schemas: Overview

– DTD (Document Type Definitions)

 _{Not written in XML}

 _{No support for data types or namespaces}

– XSD (XML Schema Definition)

 Written in XML

 _{Supports data types}

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Schemas: Purpose



Define the “rules” (grammar) of the document

– Data types

– Value bounds



A XML document that conforms to a schema

is said to be valid

– More restrictive than well-formed XML



Define which elements are present and in what order



Define the structural relationships of elements

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What is a DTD?



A DTD (

Document Type Definition

) defines the structure of a

“valid” XML document



An XML document may have an optional DTD.



Only the elements defined in a DTD can be used in an XML

document



A DTD can be



internal

The DTD is part of the document file



external

The DTD and the document are on separate files An external DTD may reside

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Connecting a Document with its DTD

 An internal DTD

<?xml version="1.0"?>

<!DOCTYPE db [<!ELEMENT ...> … ]> <db> ... </db>

 A DTD from the local file system:

<!DOCTYPE db SYSTEM "schema.dtd">

 A DTD from a remote file system:

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DTD

An internal DTD

<!DOCTYPE invoice [

<!ELEMENT invoice (sku, qty, desc, price) > <!ELEMENT sku (#PCDATA) >

<!ELEMENT qty (#PCDATA) > <!ELEMENT desc (#PCDATA) > <!ELEMENT price (#PCDATA) > }>

<desc>Left handed monkey wrench</desc> <price>14.95</price>

</invoice>

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DTD

An referenced external DTD

<?xml version=“1.0”>

<!DOCTYPE invoice SYSTEM “invoice.dtd”>

<desc>Left handed monkey wrench</desc>

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DTD

An external DTD (invoice.dtd)

<?xml version=“1.0”?>

<!ELEMENT invoice (sku, qty, desc, price) > <!ELEMENT sku (#PCDATA) >

<!ELEMENT qty (#PCDATA) > <!ELEMENT desc (#PCDATA) > <!ELEMENT price(#PCDATA) >

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DTD

Data Types



Parsed Character Data

– #PCDATA

 <!ELEMENT firstname (#PCDATA)

 <!ELEMENT lastname (#PCDATA)



Unparsed Character Data

– CDATA

 <firstname><![CDATA[Jim]]></firstname>

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DTD

XML Document

<db><person><name>Alan</name>

<age>42</age>

<email>[email protected] </email> </person>

<person>………</person> ……….

</db>

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DTD

<!DOCTYPE db [

<!ELEMENT db (person*)>

<!ELEMENT person (name, age, email)> <!ELEMENT name (#PCDATA)>

<!ELEMENT age (#PCDATA)> <!ELEMENT email (#PCDATA)> ]>

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DTD



Occurrence Indicator:

Indicator

Occurrence

(no indicator)

Required

One and only one

?

Optional

None or one

*

Optional,

repeatable

None, one, or more

+

Required,

repeatable

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Why You Should Use XSD



Newest W3C Standard



Broad support for data types



Reusable “components”

– Simple data types – Complex data types



Extensible



Inheritance support



Namespace support

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XML Schema – Better than DTDs



The purpose of a Schema is to define the legal building

blocks of an XML document, just like a DTD.



XML Schemas

 are easier to learn than DTD

 are extensible to future additions

 are richer and more useful than DTDs  are written in XML

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A Simple XML Document



Look at this simple XML document called

"note.xml":

<?xml version="1.0"?> <note>

<to>Tove</to>

<from>Jani</from>

<heading>Reminder</heading>

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A DTD File

 The following example is a DTD file called "note.dtd" that defines the elements of the XML document ("note.xml"):

<!ELEMENT note (to, from, heading, body)>

<!ELEMENT to (#PCDATA)>

<!ELEMENT from (#PCDATA)>

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An XSD

 The following example is an XML Schema file called "note.xsd" that defines the elements of the XML document ("note.xml"):

<?xml version="1.0"?> <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.w3schools.com"> <xs:element name="note"> <xs:complexType> <xs:sequence>

<xs:element name="to" type="xs:string"/> <xs:element name="from" type="xs:string"/> <xs:element name="heading" type="xs:string"/> <xs:element name="body" type="xs:string"/> </xs:sequence>

</xs:complexType> </xs:element>

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A Reference to a DTD

 This XML document has a reference to a DTD:  _{<?xml version="1.0"?>}

<!DOCTYPE note SYSTEM

"http://www.w3schools.com/dtd/note.dtd"> <note>

<heading>Reminder</heading>

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A Reference to an XSD

 This XML document has a reference to an XML Schema:

<?xml version="1.0"?> <note

xmlns="http://www.w3schools.com"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.w3schools.com note.xsd"> <to>Tove</to>

<heading>Reminder</heading>

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49

Another well-structured example

<novel>

<foreword>

<paragraph> This is the great American novel. </paragraph>

</foreword>

<chapter number="1">

<paragraph>It was a dark and stormy night. </paragraph>

<paragraph>Suddenly, a shot rang out! </paragraph>

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50

XML as a tree



An XML document represents a hierarchy; a hierarchy is a tree

novel

foreword chapter

number="1"

paragraph paragraph paragraph

This is the great American novel.

It was a dark and stormy night.

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Displaying XML



XML documents do not carry information about how to

display the data



We can add display information to XML with

– CSS (Cascading Style Sheets)

– XSL (eXtensible Stylesheet Language) --- preferred

XML, HTML,

… XML

XSLT

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XML Applications



Computer-computer communications.



Enterprise Application Integration.



Content Management Systems.



Wireless Communication Systems.



PDAs and Handheld Devices.



eLearning and Educational Services.



Web Services.

computer technology,

XML_1.ppt

Service-Oriented Computing

matter.

structured information

Documents Configuration

XML XML

“PO-1234”,”CUST001”,”X9876”,”5”,”14.98”

Benefits of XML

XML is not a replacement for HTML.

HTML XML

HTML and XML

<font face="Verdana" size="+1" color="red">

XML is for computers

<h1> Bibliography </h1>

XML-related technologies

Components of an XML Document

The Prolog (processing instructions)/XML declaration

Elements and attributes

Entities

The term CDATA is used about text data that should not be

CDATA Example

<script> <![CDATA[

Comments

The blanks after

XML may be

Elements must be properly nested,

Allow authors to differentiate between tags of the same

Namespaces: Declaration

xmlns: bk = “urn:mybookstuff.org:bookinfo”

Namespace declaration examples:

Namespace declaration Prefix URI (URL)

There are two ways to use namespaces:

<BOOK xmlns:bk=“http://www.bookstuff.org/bookinfo”> <bk:TITLE>All About XML</bk:TITLE>

Namespaces: Default Namespace

<BOOK xmlns=“http://www.bookstuff.org/bookinfo”> <TITLE>All About XML</TITLE>

Namespaces: Scope

<BOOK xmlns=“www.bookstuff.org/bookinfo”> <TITLE>All About XML</TITLE>

Namespaces: Attributes

Schemas: Purpose

What is a DTD?

external

An internal DTD

An external DTD (invoice.dtd)

<db><person><name>Alan</name>

Occurrence Indicator:

Extensible

A Simple XML Document

<?xml version="1.0"?> <note>

A DTD File

A Reference to a DTD

Another well-structured example

<novel>

XML as a tree

We can add display information to XML with