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XML DTD and Namespaces
Chapter 2

Core XML / Chapter 2 / Slide 2 of 25
Review-1
 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

Review-2
 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

Review-3
 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

Chapter Objectives
 Explain Document Type Definition
 Create Document Type Definitions:
 Declaring an Element
 Declaring Attributes
 Explain the use of DTD
 Describe namespaces

Document Type Definition (DTD)
 It is a feature of SGML, which is inherited by
XML.
 It contains the list of tags that specifies the
grammatical structure of an XML document.
 DTD defines the way elements relate to one
another within the document’s tree structure, and
specifies the attributes.
 DTD are of two types:
 An external DTD
 An internal DTD

Why Use a DTD
 DTDs are used by XML to provide an application
independent way of sharing data.
 Common DTD can be used to interchange data
between independent groups of people.
 DTD can be used by the application to verify that
valid data has been entered.
 It defines the legal building blocks of an XML
document.

Structure of a DTD
<!DOCTYPE dtd-name
[
<!ELEMENT element-
name (element-
content type) >
<!ATTLIST element-
name attribute-name
attribute-type
default-value>
]>
DOCTYPE declaration
ELEMENT declaration
ATTRIBUTE
declaration

Declaring an Element
 XML elements are declared with an element
declaration.
 Syntax
<!ELEMENT element-name (element-content
type)>
 Example
<!ELEMENT SHOWROOM (TV|LAPTOP)+>

Empty Element
 EMPTY element-content type specifies that the
element has no child elements or character data.
 Syntax
<!ELEMENT element-name (EMPTY)>
 Example
<!ELEMENT img (EMPTY)>
 Empty elements with attributes are possible:
<img src=“Tittle.gif”></img>

Elements with Data
 Syntax
<!ELEMENT element-name (#CDATA)>
or
<!ELEMENT element-name (#PCDATA)>
or
<!ELEMENT element-name (ANY)>
Where:
#CDATA = element contains character data that is not parsed
#PCDATA = element contains character data that is to be parsed
ANY = element with any content

Elements with Child
Elements Elements with one or more children are defined with the name
of the child element inside the parentheses.
 Syntax
<!ELEMENT element-name (child-element-name)>
or
<!ELEMENT element-name (child-element-name, child-element-name,.....)>
 Example
<!ELEMENT note (to, from, heading, body)>
<!ELEMENT to (#CDATA)> <!ELEMENT from (#CDATA)>
<!ELEMENT heading (#CDATA)> <!ELEMENT body
(#CDATA)>

Declaring According to the
Occurrences of Elements
Element occurrences
Only one occurrence
<!ELEMENT element-name (child-name)>
Minimum one
occurrence
<!ELEMENT
element-name
(child-name+)>
Zero or more
occurrences
<!ELEMENT
element-name
(child-
name*)>
Zero or one occurrence
<!ELEMENT element-name (child-name?)>

Declaring Mixed Content
 An element can have a mixed combination of child
elements.
 Example
<!ELEMENT note (to+, from, header,
message*,#PCDATA)>
 The sub elements and subgroups can be declared in
Sequence or Choice.

Declaring Attributes
 Elements can have attributes.
 Syntax
<!ATTLIST element-name attribute-name attribute-type
default-value>
 Example: 1
<!DOCTYPE Book
[
<!ELEMENT Book (Title, Chapter+)>
<!ATTLIST Book
Author CDATA #REQUIRED>
<!ELEMENT Chapter (#PCDATA)>
<!ATTLIST Chapter
id (4 | 7) #REQUIRED>
<!ELEMENT Title (#PCDATA)> ]>

Declaring Attributes
Example: 2

Attribute (Attribute- Type Values)
Value Explanation
CDATA The value is character data
(eval|eval|..) The value must be an enumerated value
ID The value is an unique id
IDREF The value is the id of another element
IDREFS The value is a list of other ids
NMTOKEN The value is a valid XML name
NMTOKENS The value is a list of valid XML names
ENTITY The value is an entity
ENTITIES The value is a list of entities
NOTATION The value is a name of a notation
xml: The value is predefined

Attribute (Attribute-Default-Value)
Value Explanation
#DEFAULT The attribute has a default value.
#REQUIRED
The attribute value must be included in the
element.
#IMPLIED The attribute does not have to be included.
#FIXED The attribute value is fixed.

Internal DTD
 It is written directly in
the XML document after
the XML declaration.
 Writing the DTD within
the DOCTYPE definition
is called as Wrapping.
 The file with the DTD
and XML code has a
.xml extension.
<!DOCTYPE SHOWROOM
[
<!ELEMENT SHOWROOM
(TV|LAPTOP)+>
<!ELEMENT TV (#PCDATA)>
<!ATTLIST TV
count CDATA #REQUIRED>
<!ELEMENT
LAPTOP(#PCDATA)>
<!ATTLIST LAPTOP
]
>

External DTD
 It exists outside the
content of a document.
 The DTD file has a
.dtd extension.
 The reference to the
DTD file is added at
the beginning of the
XML file.
The DTD reference in the XML
document file:
<!DOCTYPE SHOWROOM SYSTEM
"show.dtd">
The show.dtd file:
<!ELEMENT SHOWROOM
(TV|LAPTOP)+>
<!ELEMENT TV (#PCDATA)>
<!ATTLIST TV
<!ELEMENT LAPTOP (#PCDATA)>
<!ATTLIST LAPTOP

Internal Entity Declaration
 Entities that have their contents within the XML
document are called internal entities.
 Syntax
<!ENTITY entity-name "entity-value">
 Example
<!ENTITY writer “Nicole D.">
<!ENTITY copyright "Copyright Aptech Ltd.">
In XML document the entities would be referred as shown below:
<author>&writer;&copyright;</author>

External Entity Declaration
 Entities whose contents are found outside the
XML document are called external entities.
 They are declared using the SYSTEM keyword.
 Syntax
<!ENTITY entity-name SYSTEM "URI/URL">
 Example
<!ENTITY writer SYSTEM
"http://www.xml101.com/entities/entities.
xml">
<!ENTITY copyright SYSTEM
"http://www.xml101.com/entities/entities.
dtd">

XML Namespaces - 1
 Two or more applications on the Internet may also
have some element names that are common.
Namespaces help avoid such ambiguity that may
arise.
 It also allows to combine documents from different
sources and enables the identification of what
element or attributes come from which source.
 It instructs the user agent to access the DTD against
which the document is validated.

XML Namespaces - 2
 A URI(Uniform Resource Identifier) is used
to identify namespaces in XML.
 It includes Uniform Resources Name(URN)
and a Uniform Resource Locator(URL).
 URL contains the reference for a document
or an HTML page on a web.
 URN is a universally unique number that
identifies Internet resources.

Needs of a Namespace
 Namespaces are used to overcome the conflict
that arise when reuse and extension of the
DTD’s take place.
 Namespaces help standardize and uniquely
brand elements and attributes.
 Namespaces employ the URI to instruct the
user-agent about the location of the DTD
against which the XML document is checked
for validity.
 Namespaces ensure that element names do not
conflict and do clarify their origins.

Syntax for Namespace
 A prefix is associated with the URI that can be
used as a namespace.
 Syntax
xmlns:[prefix]= “[URI of namespace]”
 The xmlns: is a reserved attribute
 Example
xmlns:ins= “http://www.Aptech_edu.ac”
 Namespace needs to be declared before using
 It is declared in the root element of the document

Attributes and Namespaces
 Attributes comes within the namespace of
their element unless they are predefined.
 We can also incorporate attributes from
two domains:
<sample
xmlns= “http://www.Aptech_edu.ac”
xmlns:tea_batch= “http://www.tea.org”>
<batch-list>
<batch type=“thirdbatch”>Evening Batch</batch>
<batch tea_batch:type= “thirdbatch”>Tea batch
III </batch>
<batch>Afternoon Batch</batch>
</batch-list>
</sample>

Namespace Application
 The new XSL syntax makes use of namespace
to identify both its own tags, and the
formatting vocabulary tags.
 The xsl: prefix are in the
http//www.w3.org/TR/WD-xsl namespace.
 The fo: prefix are in the
http//www.w3.org/TR/WD-xsl/FO.
 XSL is written in XML syntax and uses tags,
elements, and attributes.

Namespace Example
<book
xmlns:html=“http//www.w3.org/TR/WD-xsl/FO”>
<index>
<chapter>this is chapter 1</chapter>
<html:br/>
<chapter>this is chapter 1</chapter>
</index>
</book>

Summary-1
 A well-formed document is one that conforms to
the basic rules of XML.
 A valid document is well formed and is also
validated against a DTD.
 The DTD specifies the grammatical structure of an
XML document, thereby allowing XML parsers to
understand and interpret the document’s contents.
 The use of the SYSTEM keyword indicates to the
parser that this is an external declaration, and that
the set of rules for this XML document can be
found in a specified file.
 EMPTY element-content type specifies that the
element has no child elements or character data.

Summary-2
 #CDATA means that the element contains character
data that is not to be parsed by a parser.
#PCDATA means that the element contains data
that is to be parsed by a parser.
 Specifying a default value for an attribute in the
DTD ensures that the attribute will get a value, even
if the author of the XML document does not include
it.
 Specifying the value of an attribute as ‘Implied’
means that the particular attribute is not mandatory
and can be specified in the XML document.
 Specifying the value of an attribute as ‘Required’
means that the particular attribute is mandatory
(that is, its value must be provided in the XML
document).

Summary-3
 ‘ID’ is the identifier type, and should be unique.
This attribute value is used to search for a
particular instance of an element. Each element
can only have one attribute of type ID.
 A DTD can be either External or Internal.
 Entities allow us to create an alias to some large
piece of text, so that, in the document, the same
piece of text can be referred to, simply by
referring to the alias.
 Namespaces allow us to combine documents from
different sources, and be able to identify which
elements or attributes come from which source.

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