WEB PROGRAMMING

Nadar saraswathi college of arts and science
Web programming
XML documents and vocabularies
XML versions and declarations
XML namespace
DTD
Submitted by,
S.Vijayalakshmi.

 An XML document is a basic unit of XML information
composed of elements and other markup in an orderly
package. An XML document can contains wide variety of
data. For example, database of numbers, numbers
representing molecular structure or a mathematical equation.
XML Document Example
?xml version = "1.0"?> <contact-info>
<name>Tanmay Patil</name>
<company>TutorialsPoint</company>
<phone>(011) 123-4567</phone>
</contact-info>

Document Prolog Section
 Document Prolog comes at the top of the document, before
the root element. This section contains −
I. XML declaration
II. Document type declaration

Document Elements Section
 Document Elements are the building blocks of XML. These
divide the document into a hierarchy of sections, each
serving a specific purpose.
 You can separate a document into multiple sections so that
they can be rendered differently, or used by a search engine.
 The elements can be containers, with a combination of text
and other elements.

XML Declaration
XML declaration contains details that prepare an XML
processor to parse the XML document. It is optional, but
when used, it must appear in the first line of the XML
document.
Syntax
<?xml version = "version_number"
encoding = "encoding_declaration"
standalone = "standalone_status" ?>
Each parameter consists of a parameter name, an equals
sign(=),and parameters value inside a quote.

Version 1.0 Specifies the version of the XML
standard used.
Encoding UTF-8, UTF-16, ISO-
10646-UCS-2, ISO-
10646-UCS-4, ISO-8859-
1 to ISO-8859-9, ISO-
2022-JP, Shift_JIS, EUC-
JP
It defines the character encoding used in
the document. UTF-8 is the default
encoding used.
Standalone yes or no It informs the parser whether the
document relies on the information from
an external source, such as external
document type definition (DTD), for its
content. The default value is set to no.
Setting it to yestells the processor there
are no external declarations required for
parsing the document.

Rules
 An XML declaration should abide with the following rules
 If the XML declaration is present in the XML, it must be
placed as the first line in the XML document.
 If the XML declaration is included, it must contain version
number attribute.
 The Parameter names and values are case-sensitive.
 The names are always in lower case.
 The order of placing the parameters is important. The correct
order is: version, encoding and standalone.
 Either single or double quotes may be used.
 The XML declaration has no closing tag i.e. </?xml>

XML Declaration Examples
XML declaration with no parameters −
<?xml >
XML declaration with version definition −
<?xml version = "1.0"> XML declaration with all parameters
defined −
<?xml version = "1.0" encoding = "UTF-8" standalone = "no"
?>
XML declaration with all parameters defined in
single quotes −
<?xml version = '1.0' encoding = 'iso-8859-1' standalone = 'no'
?>

XML Namespaces
XML Namespaces provide a method to avoid element name
conflicts.
Name Conflicts
In XML, element names are defined by the developer. This often
results in a conflict when trying to mix XML documents from different
XML applications.
This XML carries HTML table information:
<table>
<tr>
<td>Apples</td>
<td>Bananas</td>
</tr>
</table>

This XML carries information about a table (a piece of furniture):
<table>
<name>African Coffee Table</name>
<width>80</width>
<length>120</length>
</table>
 If these XML fragments were added together, there would be a name
conflict. Both contain a <table> element, but the elements have
different content and meaning.
 A user or an XML application will not know how to handle these
differences.

Solving the Name Conflict Using a Prefix
 Name conflicts in XML can easily be avoided using a name prefix.
 This XML carries information about an HTML table, and a piece of
furniture:
<h:table>
<h:tr>
<h:td>Apples</h:td>
<h:td>Bananas</h:td>
</h:tr>
</h:table>
<f:table>
<f:name>African Coffee Table</f:name>
<f:width>80</f:width>
<f:length>120</f:length>
</f:table>

XML Namespaces - The xmlns Attribute
 When using prefixes in XML, a namespace for the prefix
must be defined.
 The namespace can be defined by an xmlns attribute in the
start tag of an element.
 The namespace declaration has the following syntax.
xmlns:prefix="URI".
<root>
<h:table xmlns:h="http://www.w3.org/TR/html4/">
<h:tr>
<h:td>Apples</h:td>
</h:tr>
</h:table>

<f:tablexmlns:f="https://www.w3schools.com/furniture">
</f:table>
</root>
 In the example above:
 The xmlns attribute in the first <table> element gives the h:
prefix a qualified namespace.
 The xmlns attribute in the second <table> element gives the f:
prefix a qualified namespace.
 When a namespace is defined for an element, all child elements
with the same prefix are associated with the same namespace.
 Namespaces can also be declared in the XML root element:

<root xmlns:h="http://www.w3.org/TR/html4/"
xmlns:f="https://www.w3schools.com/furniture">
<h:table>
<h:tr>
<h:td>Apples</h:td>
</h:tr>
</h:table>
<f:table>
</f:table>
</root>
 The purpose of using an URI is to give the namespace a unique name.
 However, companies often use the namespace as a pointer to a web
page containing namespace information.

Uniform Resource Identifier (URI)
 A Uniform Resource Identifier (URI) is a string of characters
which identifies an Internet Resource.
 The most common URI is the Uniform Resource
Locator (URL) which identifies an Internet domain address.
Another, not so common type of URI is the Uniform Resource
Name (URN).
Default Namespaces
 Defining a default namespace for an element saves us from
using prefixes in all the child elements. It has the following
syntax:
xmlns="namespaceURI"

DTD[Document Type Definition]
 The XML Document Type Declaration, commonly known as DTD, is
a way to describe XML language precisely. DTDs check vocabulary
and validity of the structure of XML documents against grammatical
rules of appropriate XML language.
 An XML DTD can be either specified inside the document, or it can be
kept in a separate document and then liked separately.
Syntax
<!DOCTYPE element DTD identifier
[ declaration1
declaration2 ........ ]>

 In the above syntax,
 The DTD starts with <!DOCTYPE delimiter.
 An element tells the parser to parse the document from
the specified root element.
 DTD identifier is an identifier for the document type
definition, which may be the path to a file on the system
or URL to a file on the internet. If the DTD is pointing
to external path, it is called External Subset.
 The square brackets [ ] enclose an optional list of entity
declarations called Internal Subset.

Internal DTD
 A DTD is referred to as an internal DTD if elements are
declared within the XML files. To refer it as internal
DTD, standaloneattribute in XML declaration must be set
to yes. This means, the declaration works independent of an
external source.
Syntax
<!DOCTYPE root-element [element-declarations]>
 where root-element is the name of root element
and element-declarations is where you declare the elements.

Example
xml version = "1.0" encoding = "UTF-8" standalone = "yes"
?>
<!DOCTYPE address [ <!ELEMENT address
(name,company,phone)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT company (#PCDATA)>
<!ELEMENT phone (#PCDATA)>
]>
<address>
<phone>(011) 123-4567</phone>
</address>

External DTD
In external DTD elements are declared outside the XML file. They are
accessed by specifying the system attributes which may be either the
legal .dtd file or a valid URL. To refer it as external
DTD,standalone attribute in the XML declaration must be set as no.
This means, declaration includes information from the external source.
Syntax
<!DOCTYPE root-element SYSTEM "file-name
 where file-name is the file with .dtd extension.

Example
<?xml version = "1.0" encoding = "UTF-8" standalone =
"no" ?>
<!DOCTYPE address SYSTEM "address.dtd"> <address>
<phone>(011) 123-4567</phone>
</address>

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