Fundamental XML for Developers pps

Document begins with declaration that specifies XML version 1.0 Element message is child element of root element myMessage... Parsing an XML Document with MSXML • XML document – Contai

Fundamental XML for

Developers

Dr Timothy M Chester Texas A&M University

Timothy M Chester is .

• Senior IT Manager, Texas A&M University

– Application Development, Systems Integration, Developer Tools

& Training

• Lecturer, Texas A&M College of Business

– Courses on Business Programming Fundamentals (VB.NET, C#), XML & Advanced Web Development.

Texas A&M University

– Interested in how XML can affect both

software development and legacy system integration

• Demonstrates some of the basics of

working with the DOM, XSLT, Schema,

WSDL, and SOAP.

Other Web Services

Partner Web Service

Partner Web Service

Introducing XML

• XML stands for Extensible Markup

Language A markup language specifies the structure and content of a document.

• Because it is extensible, XML can be used

to create a wide variety of document

types.

between SGML and HTML – easier to learn than

The Limits of HTML

• HTML was designed for formatting text on a Web page

It was not designed for dealing with the content of a Web page Additional features have been added to HTML, but they do not solve data description or cataloging issues in

an HTML document.

• 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.

Document begins with declaration

that specifies XML version 1.0

Element message is

child element of root

element myMessage

• XML documents

– Must contain exactly one root element

• Attempting to create more than one root element is erroneous

– Elements must be nested properly

• Incorrect: <x><y> hello </x></y>

• Correct: <x><y> hello </y></x>

– Must be well-formed

Introduction to XML Markup

(cont.)

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

Parsers and Well-formed XML

Documents (cont.)

• XML parsers support

– Document Object Model (DOM)

• Builds tree structure containing document data in memory

– Simple API for XML (SAX)

• Generates events when tags, comments, etc are

encountered

– (Events are notifications to the application)

Parsing an XML Document with

MSXML

• XML document

– Contains data

– Does not contain formatting information

– Load XML document into Internet Explorer 5.0

• Document is parsed by msxml.

• Places plus (+) or minus (-) signs next to container elements

– Plus sign indicates that all child elements are hidden – Clicking plus sign expands container element

» Displays children – Minus sign indicates that all child elements are visible – Clicking minus sign collapses container element

» Hides children

• Error generated, if document is not well formed

XML document shown in IE6.

Characters vs Markup

• XML must differentiate between

– Markup text

• Enclosed in angle brackets (< and >)

– e.g, Child elements– Character data

• Text between start tag and end tag

– Welcome to XML!

– Elements versus Attributes

White Space, Entity References

and Built-in Entities

• Whitespace characters

– Spaces, tabs, line feeds and carriage returns

• Significant (preserved by application)

• Insignificant (not preserved by application)

– Normalization

» Whitespace collapsed into single whitespace character

» Sometimes whitespace removed entirely

<markup> This is character data </markup>

after normalization, becomes

<markup> This is character data </markup>

White Space, Entity References and

Built-in Entities (cont.)

– Allow to use XML-reserved characters

• Begin with ampersand (&) and end with semicolon (;)

– Prevents from misinterpreting character data as markup

White Space, Entity References

and Built-in Entities (cont.)

• Build-in entities

– Ampersand (&amp;)

– Left-angle bracket (&lt;)

– Right-angle bracket (&gt;)

– Apostrophe (&apos;)

– Quotation mark (&quot;)

– Mark up characters “<>&” in element

message

<message> &lt;&gt;&amp; </message>

• XML Document Object Model (DOM)

– Build tree structure in memory for XML

documents

– DOM-based parsers parse these structures

• Exist in several languages (Java, C, C++, Python, Perl, C#, VB.NET, VB, etc)

<message from = "Paul" to = "Tem" >

<body> Hi, Tim! </body>

</message>

• Node created for element message

Creating Nodes

• Create XML document at run time

Traversing the DOM

• Use DOM to traverse XML document

– Output element nodes

– Output attribute nodes

– Output text nodes

DOM Components

• Manipulate XML document

• XML Path Language (XPath)

– Syntax for locating information in XML document

• e.g., attribute values

– String-based language of expressions

• Not structural language like XML

– Used by other XML technologies

• XSLT

• XML document

– Tree structure with nodes

– Each node represents part of XML document

• Seven types

– Root – Element – Attribute – Text – Comment – Processing instruction – Namespace

• Attributes and namespaces are not children of their parent node

– They describe their parent node

XPath node types

Node Type string-value expanded-name Description

root Determined by

concatenating the string-values of all text- node descendents in document order

None Represents the root of an

XML document This node exists only at the top of the tree and may contain element, comment or processor-

instruction children

element Determined by

concatenating the string-values of all text- node descendents in document order

The element tag, including the namespace prefix (if applicable)

Represents an XML element and may contain element, text, comment or processor-

Represents an attribute of an element

XPath node types (Part 2)

contained in the text node

data content of an element

(not including <! and >)

The target of the processing instruction

Represents an XML processing instruction

prefix

Represents an XML namespace

Location Paths

• Location path

– Expression specifying how to navigate XPath tree

– Composed of location steps

• Each location step composed of

– Axis – Node test – Predicate

• XPath searches are made relative to

context node

• Axis

– Indicates which nodes are included in search

• Relative to context node

– Dictates node ordering in set

• Forward axes select nodes that follow context node

• Reverse axes select nodes that precede context node

Node Tests

• Node tests

– Refine set of nodes selected by axis

• Rely upon axis’ principle node type

– Corresponds to type of node axis can select

Node-set Operators and

Functions (cont.)

• Location-path expressions

– Combine node-set operators and functions

• Select all head and body children element nodes

• Extensible Stylesheet Language (XSL)

– Used to format XML documents

– Consist of two parts

• XSLT processor

– Microsoft Internet Explorer 6

– Java 2 Standard Edition

– Microsoft.NET System.Xml Namespace

• XSLT document

– XML document with root element stylesheet

– template element

• Matches specific XML document nodes

• Uses XPath expression in attribute match

Templates (cont.)

• XSLT

– Two trees of nodes

• Source tree corresponds to original XML document

• Result tree contains nodes produced by transformation

– Transforms intro.xml into HTML document

Iteration and Sorting

Conditional Processing

• Perform conditional processing

– Such as if statement

– Use element choose

• Allows alternate conditional statements

• Similar to switch statement

• Has child elements when and otherwise

– when element content used if condition is met – otherwise element content used if no conditions in

XSLT and XPath

• XPath Expression

– locates elements, attributes and text in XML document

Working with Namespaces

• Name collision occurs when elements from two

or more documents share the same name

• Name collision isn’t a problem if you are not

concerned with validation The document

content only needs to be well-formed

• However, name collision will keep a document from being validated

Name Collision

This figure shows two documents each with a Name

element

Using Namespaces to Avoid

Name Collision

This figure shows how to use a namespace to avoid collision

Declaring a Namespace

• A namespace is a defined collection of element

and attribute names

• Names that belong to the same namespace

must be unique Elements can share the same name if they reside in different namespaces

• Namespaces must be declared before they can

be used

Declaring a Namespace

• A namespace can be declared in the prolog or as an

element attribute The syntax to declare a namespace in the prolog is:

<?xml:namespace ns=“URI” prefix=“prefix”?>

• Where URI is a Uniform Resource Identifier that assigns

a unique name to the namespace, and prefix is a string

of letters that associates each element or attribute in the document with the declared namespace.

9 <text:file filename = "book.xml" >

10 <text:description> A book list </text:description>

11 </text:file>

12

13 <image:file filename = "funny.jpg" >

14 <image:description> A funny picture 15 </image:description> <image:size width = "200" height = "100" />

16 </image:file>

17

18 </directory>

9 <file filename = "book.xml" >

10 <description> A book list </description>

11 </file>

12

13 <image:file filename = "funny.jpg" >

14 <image:description> A funny picture 15 </image:description> <image:size width = "200" height = "100" />

• A schema is an XML document that defines the content

and structure of one or more XML documents.

• To avoid confusion, the XML document containing the

content is called the instance document.

• It represents a specific instance of the structure defined

in the schema.

Comparing Schemas and DTDs

This figure compares schemas and DTDs

Schema Dialects

• There is no single schema form.

• Several schema “dialects” have been

developed in the XML language.

• Support for a particular schema depends

on the XML parser being used for

validation.

Starting a Schema File

• A schema is always placed in a separate XML document that is referenced by the instance document.

Schema Types

• XML Schema recognize two categories of element types: complex and simple.

• A complex type element has one or more

attributes, or is the parent to one or more child elements.

• A simple type element contains only

character data and has no attributes.

Schema Types

This figure shows types of elements

Understanding Data Types

• XML Schema supports two data types: built-in

and user-derived

• A built-in data type is part of the XML Schema

specifications and is available to all XML

Schema authors

• A user-derived data type is created by the XML

Schema author for specific data values in the

instance document

Understanding Data Types

• A primitive data type, also called a base

type, is one of 19 fundamental data types not defined in terms of other types.

• A derived data type is a collection of 25

data types that the XML Schema

developers created based on the 19

• Think "TypeLib for SOAP"

• WSDL = Web Service Description Language

• Uniform representation for services

– Transport Protocol neutral – Access Protocol neutral (not only SOAP)

• Describes:

– Schema for Data Types – Call Signatures (Message) – Interfaces (Port Types) – Endpoint Mappings (Bindings)

• Think "Yahoo!" for WebServices

• Universal Description and Discovery Interface

• WebService-Programmable "Yellow Pages"

• Advertise Sites and Services

• May point to DISCO resources

• Initiative driven by Microsoft, IBM,

Ariba

• A lightweight protocol for exchanging information

in a distributed, heterogeneous environment

– It enables cross-platform interoperability

• Guiding principle: “Invent no new technology”

• Builds on key Internet standards

– SOAP ≈ HTTP + XML

– Submitted to W3C

• The SOAP specification defines:

– The SOAP message format

– How to send messages

– How to receive responses

SOAP

Overview

<Header> encloses headers

<Envelope> encloses payload

Protocol binding headers The complete SOAP message

SOAP

Message Structure

SOAP Message Format

• An XML document using the SOAP schema:

</AddResult>

</soap:Body>

</soap:Envelope>

Questions

• Harvey Deitel’s “XML:How To Program”

• Prentice Hall XML Reference

• Microsoft Academic Resource Kit