2 XML Basics

8/14/2019 2 XML Basics

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XML

Basics


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Topics

Basic XML document structure and

components

Well-formed XML DTD DTD components Creating DTD and linking with XML

document XML parsers Valid XML document


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Harry Potter

Ron

Reminder

Please, get your magicwand.

"

Root element

Empty Element

Attribute

XML document structure

Element

Comment

Processing instruction

Entity Reference


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Special markup characters

&

Use < for for >

Use & for &

Use ' for

Use &quot for


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Redefining XML

An XML document is an information

unit that can be viewed in two ways:

as a linear sequence of charactersthat contain character data or

markup or entity references

or as an abstract data structure that

is a tree of nodes.


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Well-formed Constraints

All XML elements must nest correctly.

XML tags are case sensitive. The case of the

start tag and and its corresponding end tag

must match.

All XML elements must be properly nested

All XML documents must have one and only

one Root element

All the elements (other than the root)must

have one and one parent.


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Well-formed Constraints

Attribute values must always be quoted

Empty tags must end with a /.

An XML document that confirms to theabove rules is called a Well formed

XML document


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Well-formed XML data conforms to the

XML syntax specification, and includes no

references to external resources (unlessa DTD is provided). It is comprised of

elements that form a hierarchical tree,

with a single root node (the document

element).

Well-formed XML defined


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Example: XHTML

Well-formed document:XHTML document

This is a well-formed HTMLdocument

and valid XHTML document.


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Tool to check well-formed

XHTML document HTML Tidy utility by W3C can be used to test

for well-formed XHTML.

It can also be used to convert HTMLdocument to XHTML document.

Open source software.

Command: tidy xml e filename.xhtml


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Activity

Test the ill-formed XHTML document using

tidy and note down the errors.


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More about the XML names XML names are names given for elements

and attributes

All XML names must begin with a letter or _

or :.

Letter could be any alphabets in english orany language supported by UNICODE.

Only restriction is that it cannot be XML or

xml or mix of case in the string xml.

Patient

DOCTOR

Doctor:Patient

Xml_Tag

-Name

12Street

Legal Illegal


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Element

Basic building block of the XML document

May have

Entity referencesCommentsPIsCDATA section

Character dataAttributesCharacter references

The root element is also called the DocumentElement.


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Attributes

Attributes are used to attach theinformation about the element.

Attribute is a name-value pair

Attribute values can be any text, entityreference or character reference.

Attribute values cannot contain special

characters. Only one instance of attribute name is

allowed.


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Character references Characters that cannot be typed into a

document straight away but must be displayed,can be represented as character references.

Example: copy right symbol: , ScicomInfrastructure Pvt (India)Ltd

Used for representing a single character. It is comprised of a decimal or hexa-decimal

number between and ;


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Entity references

5 built in entity references < >etc.

Apart from these 5 entities, number of otherentity references are also defined like

etc.


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CDATA section

Character data that you dont want to be

parsed can be kept in CDATA section.

if(a>b && a


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Comment and PI

Comment can be given between Example:

Processing instruction is used to pass some

hints/files to the application along with the xml

document.

PI is given between two ?

Example:


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DTD

Document Type Definition

The DTD defines the structure of the xml

document and how content is nested.

An XML document is valid only when it iswell-formed and confirms to the DTD (or XML

schema) defined for it.

DTD defines the grammar rules for formingan XML document.


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XML Parser

XML parsers/processors are which check if theXML document is well-formed parser) or valid

Non-validating parser: ensure that the XML

document is well-formed. Validating parser: ensure that the XML

document is

Well-formed

Valid

Resolves external resources


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xml doc

xml parser

xml application

xml docreturn valid/invalid

document


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XML Parser available

Apache Xerces-C(C++) Xerces-J(Java)

IBM IBM 4C(C++) IBM4J (Java)

Microsoft MSXML IE

Oracle XML Parser for

Java

XML parser for Cand C++

Sun

JAXP and JAXBAPI


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Ways of DTD with XML

Internal

Including DTD in the same file as XML file

External Creating another file for DTD and linking it

with XML file

If both are provided, then if there are similar

declarations, internal DTD takes preference.


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Linking external DTD with XML

2 ways to associate DTD with XML1.

SYSTEM is used to explicitly specify thelocation of the DTD.

Example:

2. PUBLIC is used if the DTD is a

standard and is shared by manyorganizations


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The identifier is a name mapped to theactual location of DTD from whereeverybody shares the dtd.

If the dtd is not accessible or available then

like SYSTEM command dtd is obtainedfrom location. Example


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Basic DTD declarations


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ELEMENT Declaration

1. Text Only: Specifies that this element can contain

content that is text

Example:

VALID XML : ravi INVALID XML:ravi


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ELEMENT Declaration1. Element Only:

Specifies that this element can containelements as specified by the tag

Example:

VALID XML :

ravi

INVALID XML:

ravinath


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Order of elements

Sequence list: , separated list The child elements must appear in the

specified order

Example:

VALID XML :ravinath INVALID XML:ravi

nath


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Order of elements Choice list:

| separated list The child elements can appear any order

Example:

VALID XML :

ravi

nath

INVALID XML:

ravi


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Element Declaration1. Mixed content:

Specifies that this element can contain mixture ofelements and text as specified

Example:

Valid XML:Mr. Mohan Lal

172 Veera Apts., MG Road

Cochin

Kerala

Or |


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Element Declaration1. Anything:

Specifies that this element can containany well-formed xml data

Example: Valid XML:

Mr. Mohan Lal172 Veera Apts., MG RoadCochinKerala


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Element Declaration

Cardinality none: the absence of cardinality indicates

one and only one

*

0 or more + 1 or more

?0 or 1

Example:


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]>

Mocha Java11.95

Example:

Embedded

DTD withXML


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Validating using XMLSpy

We will use XML Spy 2.5 trial version for

DTD-Validation.

XML Spy is Microsoft XML Parser.


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Activity

Open a valid XML file with XMLSpy.

Try adding an invalid element.


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Attribute Declaration

elementName ,attrName are compulsory

type type specifies the type of the value theattribute can hold

attDefault specifies whether an attributespresence is required or not. Also says how the

parser must handle the attributes absence. Value specifies the default value


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Attribute Types

CDATA: text data (string) ID: valid xml name which is unique for each

identifier for each instance of the current element.

IDREF: a reference to the ID type IDREFS: List ofIDREFs separated by comma

NMTOKEN: text data that can contain thecharacters limited to letters, digits, underscores,

colons, periods and dashes

NMTOKENS: a comma-separated list ofNMTOKENitems


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Attribute Types

ENTITY: name of the predefined entity.

ENTITIES: a list of ENTITY names

separated by white space charsNOTATION: used to map a reference to anotation-type declaration section that is

declared else where in the DTD.

Enumerated value/attribute choice list: a list

of values that attribute value can have


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Example1


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Example1

title CDATA #REQUIRED

ISBN ID #REQUIREDSimilar IDREF #IMPLIED

libno NMTOKEN #IMPLIED

authors NMTOKENS #REQUIREDhardbound (YES|NO) "NO"

source CDATA #FIXED "BOOK"

> ]>


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Turning mistakes into stepping stonesfor success


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Notation

Notation is used to map a reference to a

notation-type declaration section that is

declared else where in the DTD.

The notation is more important for the application

outside the parser. Example:

http://mysite.com/GIF_viewer.exe>


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Entities

Entity/Entities are replaceable contents whichhelps reduced re-type or reassign of the samecontent

All the entities except predefined entities need

to be declared.

Entities can be classified in two ways: Depending on where it is used

Depending on how it is parsed


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Classification 1

Two types of Entities: Parameter Entity: Entity reference within used

within the DTD.

General Entity: Entity reference within used

within the XML document.

It is an error to put a parameter reference inthe xml document. But it is not an error to putan entity reference in DTD in defining thevalue of another entity. But the reference willnot be resolved until it is used in thedocument.


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Entity declaration

DTD

entity>

%ParEntity;

IN XML:

&GenEntity;


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Another classification

Parsed Entities: well-formed content which isparsed

Unparsed Entities: non-XML data

Unparsed entities depend on the notationdeclaration to identify them so that the

application processing the XML documentknows what kind of entity is being used andwhat to do with it.


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Example: Parsed Entity

In DTD

reserved>

&rights; >

In XML:

&book;


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Example: Unparsed Entity

In DTD:

In XML:

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