Xml theory 2005_[ngohaianh.info]_1_introduction-to-xml

Chapter Objectives -1
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Discuss markup language
List and explain drawbacks of HTML
Discuss the architecture of XML documents
List the benefits of XML
Discuss Parser

Core XML / Chapter 1 / Slide 2 of 35

Chapter Objectives -2


Build a complete XML Document:
Character Data
 Comments
 Processing Instructions
 Entities
 General Entities
 Parameter Entities
 The DOCTYPE Declarations



History of Markup
Documents recorded
using paper and pen

Typesetters formatting
documents

Tools used by typesetters
to format a document


Markup Language




A Markup language defines the rules that help to add
meaning to the content and structure of documents.
They are classified as:






Stylistic Markup – It determines the presentation of the
document
Structure Markup – It defines the structure of the
document
Semantic Markup – It determines the content of the
document

SGML






Generalized Markup Language (GML) is
the system of formatting documents.
GML was fine-tuned and came to be known
as Standard Generalized Markup Language
(SGML).
SGML is the source of origin of all markup
languages

Features of SGML




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It describes markup language, which allows
authors to create their own tags that relate to
their content.
It needs a separate file that will contain all
the rules for the language, for its
interpretation
A SGML application is markup language
derived from SGML.

HTML






HTML is the most famous markup language
derived from SGML.
It was created to mark up technical papers so that
they could be transferred across different
platforms for the scientific community.
It is now also used by those non-scientific users
who are concerned about their document‟s
presentation.


Drawbacks of HTML
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Fixed tag set
Presentation technology does not relate to the
contents
It is flat
Clogging
HTML is not international
Data interchange is impossible
Does not have a robust linking mechanism
HTML is not reusable

HTML and XML code Examples
<UL>
<LI>
<UL>
<LI>
<LI>
<LI>
<LI>
<LI>
St.
<LI>
<LI>
<LI>
</UL>
</UL>

HTML Code

TOM CRUISE

CLIENT ID : 100
COMPANY : XYZ Corp.
Email : tom@usa.net
Phone : 3336767
Street Adress: 25th
City : Toronto
State : Toronto
Zip : 20056

XML Code
<Details>
<CONTACT>
<PERSON_NAME>TOM CRUISE
</PERSON_NAME>
<ID>
100
</ID>
<Company>XYZ Corp. </Company>
<Email> tom@usa.net</Email>
<Phone> 3336767 </Phone>
<Street> 25th St.
</Street>
<City> Toronto
</City>
<State> Toronto </State>
<ZIP> 20056
</ZIP>
</CONTACT>
</Details>

XML -1
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XML stands for Extensible Markup Language.
It overcomes all the drawbacks of HTML.
It allows the user to define their own set of tags, and
also makes it possible for others (people or programs)
to understand it.
It is more flexible than HTML.
It inherits the features of SGML and combines it with
the features of HTML.
It is a smaller version of SGML.

XML -2








XML is a metalanguage and it describes other
languages.
The data contained in an XML file can be
displayed in different ways.
It can also be offered to other applications for
further processing.
Style sheets help transform structured data into
different HTML views. This enables data to be
displayed on different browsers.

XML Architecture - 1








XML supports three-tier architecture for handling
and manipulating data.
It can be generated from existing databases using a
scalable three-tier model.
XML tags represent the logical structure of data
that can be interpreted and used in various ways
by different applications.
The middle-tier is used to access multiple
databases and translate data into XML.

XML Architecture -2


XML – A Universal data format







HTML is a single markup language, but XML is a
family of markup languages.
Any type of data can be easily defined in XML.
XML is popular because it supports a wide range
of applications and is easy to use.
XML has a structured data format, which allows it
to store complex data


Benefits of XML




The three-tier architecture has easier
scalability and better security.
The benefits of XML are classified into the
following:
Business benefits
 Technological benefits



Business Benefits


Information sharing:





XML inside a single application:




Allows businesses to define data formats in XML
Provides tools to read, write and transform data
between XML and other formats
Powerful, flexible and extensible language

Content Delivery:


Supports different users and channels, like digital TV,
phone, web and multimedia kiosks

Technological Benefits
Separation of data
and presentation

Semantic
information

Technological
Benefits

Extensibility

Re-use of data


XML Document Structure







An XML document is composed of sets of
“entities” identified by unique names.
All documents begin with a root or document
entity.
Entities are aliases for more complex functions.
Documents are logically composed of
declarations, elements, comments, character
references, and processing instructions.

Well formed and Valid Documents
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An XML document is considered as well formed,
if a minimum set of requirements defined in the
XML 1.0 specification are satisfied.
The requirements ensure that correct language
terms are used in the right manner .
A valid XML document is a well-formed XML
document, which conforms to the rules of a
Document Type Definition (DTD).
DTD defines the rules that an XML markup in the
XML document must follow.

Parsers - 1


Parsers help the computer interpret an XML
file.
<?xml
version=“1.0”?
>
<nxn> </nxn>

Editor with the
XML document



XML document parsed by the
parser

Parsed document
viewed in the browser

Their are two types of parsers:
Non Validating parser
Validating parser



Parsers - 2
XML
file
Parsers load the XML
and other related files
to check whether the
XML document is
well formed and valid
Other related
files (like
DTD file)

Data tree


Data versus Markup
Markup

<NAME>

Tom Cruise

</NAME>

Data


Creating an XML Document


To create an XML document:
State an XML declaration
 Create a root element
 Create the XML code
 Verify the document



Stating an XML Declaration


Syntax

<?xml version=“1.0” standalone=“no” encoding=“UTP-8”?>
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




„Standalone‟ and „encoding‟ attributes are
optional, only the version number is mandatory
„Standalone‟ – is the external declaration
„Encoding‟ - specifies the character encoding
used by the author
XML 1.0 version is default

Creating a Root Element





There can only be one root element
It describes the function of the document
Every XML document must have a root
element

Example
<?xml version=“1.0” standalone=“no” encoding=“UTP-8”?>

<BOOK>
</BOOK>

Creating the XML Code -1





It is the process of creating our own elements and
attributes as required by our application.
Elements are the basic units of XML content.
Tags tell the user agent to do something to the
content encased between the start and end tag.
Opening Tag

Parts of an
element

<TITLE>

Content

Closing Tag

Aptech Ltd

</TITLE>

Element

Creating the XML Code -2


Rules govern the elements:
At least one element required
 XML tags are case sensitive
 End the tags correctly
 Nest tags Properly
 Use legal tags
 Length of markup names
 Define Valid Attributes



Verify the document


The document should follow the
XML rules; otherwise it will not be
read by the browser or by any other
XML reader


Comments


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This is information for the understanding of
the user, and is to be ignored by the
processor.
Syntax
<!- - Write the comment here -- >

Example

<NAME>TOM CRUISE</NAME>

The example given will
display only the name
TOM CRUSIE, and others
are treated as comments.

Processing Instruction
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A processing information is a bit of information
meant for the application using the XML document.
These instructions are directly passed to the
application using the parser.
The XML declaration is also a processing agent.
<?xml:stylesheet type=“text/xsl”?>

Name of application

Instruction information

Character Data
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The text between the start and end tags is
defined as „character data‟.
Character data may be any legal (Unicode).
Character data is classified into:
PCDATA
 CDATA



PCDATA
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It stands for parsed character data.
PCDATA is text that will be parsed by a Parser.
Tags inside the text will be treated as markup and
entities will be expanded.
Entity Name
<
>
&
"
'

Character
<
>
&
"
'

Predefined entities


CDATA
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



It means character data.
It will not be parsed by the Parser.
CDATA are used to make it convenient to include
large blocks of special characters.
The character string ]]> is not allowed within a
CDATA block as it will signal the end of the
CDATA block.

Example

<SAMPLE>
<![CDATA[<DOCUMENT>
<NAME>TOM CRUISE</NAME>
<EMAIL>tom@usa.com</EMAIL>
</DOCUMENT>]]>
</SAMPLE>

Entities




Entities are used to avoid typing long pieces of
text repeatedly within a document.
There are two categories of entities:


General entities
Syntax
<!ENTITY ADDRESS "text that is to be represented
by an entity">



Parameter entities
Syntax
<!ENTITY % ADDRESS "text that is to be represented by an entity">


Examples of Entities
An example of Parameter entities
< CLIENT = "&APTECH;"
PRODUCT = "&PRODUCT_ID;"
QUANTITY = "15">

Entity declaration
 Syntax
%PARAMETER_ENTITY_NA
ME;
 Example
%address;

An example of a General entity
<!ENTITY full_address " My
Address 12 Tenth Ave. Suite 12
Paris, France">

Entity declaration
 Syntax
&ENTITY_NAME;
 Example
&address;


The DOCTYPE declarations




The <!DOCTYPE [..]> declaration follows the
XML declaration in an XML document.
Syntax
<?xml version="1.0"?>
<!DOCTYPE myDoc [
...declare the entities here....
<myDoc>
...body of the document....
</myDoc>
Example
<!DOCTYPE CUSTOMERS [
<!ENTITY firstFloor "15 Downing St Floor 1">
<!ENTITY secondFloor "15 Downing St Floor 2">
<!ENTITY thirdFloor "15 Downing St Floor 3">
]>

Attributes


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

An attribute gives information about an
element.
Attributes are embedded in the element start
tag.
An attribute consists of an attribute name
and attribute value.

Example
<TV count="8">SONY</TV>
<LAPTOP count="10">IBM</LAPTOP>

Summary-1
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



A markup language defines a set of rules that adds
meaning to the content and structure of documents
XML is extensible, which means that we can define our
own set of tags, and make it possible for other parties
(people or programs) to know and understand these
tags. This makes XML much more flexible than HTML
XML inherits features from SGML and includes the
features of HTML. XML can be generated from
existing databases using a scalable three-tier model.
XML-based data does not contain information about
how data should be displayed
An XML document is composed of a set of “entities”
identified by unique names

Summary-2
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




A well-formed document is one that conforms to the
basic rules of XML; a valid document is a well-formed
document that conforms to the rules of a DTD
(Document Type Definition)
The parser helps the computer to interpret an XML file
Steps involved in the building of an XML document
are:
 Stating an XML declaration
 Creating a root element
 Creating the XML code
 Verifying the document
Character data is classified into PCDATA and CDATA

Summary-3
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


Entities are used to avoid typing long pieces of text
repeatedly in a document. The two types of entities
are:
 General entities
 Parameter entities
The <!DOCTYPE […]> declaration follows the
XML declaration in an XML document.
An attribute gives information about an element


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