This document provides an overview of XML (Extensible Markup Language) including its introduction, syntax, documents, declaration, tags, elements, attributes, comments, character entities, CDATA sections, whitespace, processing, encoding, validation, DTDs, schemas, tree structure, and DOM. XML is a text-based markup language that is commonly used for data storage and transmission. It has defined rules for encoding documents in a format that is both human-readable and machine-readable.

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XML
Prepared by Sruthi JS
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1 XML - Introduction
2 XML - Syntax
3 XML - Documents
4 XML - Declaration
5 XML - Tags
6 XML - Elements
7 XML - Attributes
8 XML - Comments
9 XML - Character Entities
10 XML - CDATA Sections
11 XML - WhiteSpaces
12 XML - Processing
13 XML - Encoding
14 XML - Validation
15 XML - DTDs
16 XML - Schemas
17 XML - Tree Structure
18 XML - DOM
19 XML - Namespaces
20 XML - Databases
21 XML - Viewers
22 XML - Editors
23 XML - Parsers
24 XML - Processors

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XML - introduction
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1. XML - Introduction
➔ XML stands for Extensible Markup Language.
➔ It is a text-based markup language derived from Standard Generalized Markup Language
(SGML).
Is XML a Programming Language?
➔ A programming language consists of grammar rules and its own vocabulary which is used to
create computer programs. These programs instruct the computer to perform specific tasks.
➔ XML does not qualify to be a programming language as it does not perform any computation or
algorithms. It is usually stored in a simple text file and is processed by special software that is
capable of interpreting XML.
Advantages of xml
➔ XML uses human, not computer, language. XML is readable and understandable, even by
novices, and no more difficult to code than HTML.
➔ XML is completely compatible with Java™ and 100% portable. Any application that can
process XML can use our information, regardless of platform.
➔ XML is extendable. Create our own tags, or use tags created by others, that use the natural
language of our domain, that have the attributes we need, and that makes sense to us and our
users. 4

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XML - Syntax
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2. XML - Syntax
➔ The following diagram depicts the syntax rules to write different types of
markup and text in an XML document.
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XML - Documents
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3. XML - Documents
➔ 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.
➔ The following image depicts the parts of XML document.
Document Prolog Section :
➔ Document Prolog comes at the top of the document, before the root element.
➔ This section contains −
◆ XML declaration
◆ 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.
➔ We 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. 8

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XML - Declaration
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4. 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
➔ 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 lowercase.
◆ 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>
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XML - Tags
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5. XML - Tags
➔ XML tags form the foundation of XML.
➔ They define the scope of an element in XML.
➔ They can also be used to insert comments, declare settings required for
parsing the environment, and to insert special instructions.
➔ We can broadly categorize XML tags as follows −
◆ Start Tag : The beginning of every non-empty XML element is marked by a start-tag.
◆ End Tag : Every element that has a start tag should end with an end-tag.
◆ Empty Tag : The text that appears between start-tag and end-tag is called content. An
element which has no content is termed as empty.
➔ Rules
◆ XML tags are case-sensitive.
◆ XML tags must be closed in an appropriate order, i.e., an XML tag opened inside another
element must be closed before the outer element is closed.
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XML - Elements
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6. XML - Elements
➔ XML elements can be defined as building blocks of an XML.
➔ Elements can behave as containers to hold text, elements, attributes, media objects or all
of these.
➔ Each XML document contains one or more elements, the scope of which are either
delimited by start and end tags, or for empty elements, by an empty-element tag.
➔ Syntax
➔ Example
➔ Rules
◆ An element name can contain any alphanumeric characters. The only punctuation mark allowed in
names are the hyphen (-), underscore (_) and period (.).
◆ Names are case sensitive. For example, Address, address, and ADDRESS are different names.
◆ Start and end tags of an element must be identical.
◆ An element, which is a container, can contain text or elements as seen in the above example.
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XML - Attributes
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7. XML - Attributes
➔ Attributes are part of XML elements. An element can have multiple unique
attributes.
➔ Attribute gives more information about XML elements. To be more precise,
they define properties of elements. An XML attribute is always a name-
value pair.
➔ Rules
◆ An attribute name must not appear more than once in the same start-tag or empty-
element tag.
◆ An attribute must be declared in the Document Type Definition (DTD) using an Attribute-
List Declaration.
◆ Attribute values must not contain direct or indirect entity references to external entities.
◆ The replacement text of any entity referred to directly or indirectly in an attribute value
must not contain a less than sign (<)
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7. XML - Attributes (cond…)
➔ Example
◆ Attributes are used to distinguish among elements of the same name, when we do not
want to create a new element for every situation. Hence, the use of an attribute can add a
little more detail in differentiating two or more similar elements.
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XML - Comments
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8. XML - Comments
➔ XML comments are similar to HTML comments. The comments are added
as notes or lines for understanding the purpose of an XML code.
➔ Comments can be used to include related links, information, and terms.
They are visible only in the source code; not in the XML code.
➔ Comments may appear anywhere in XML code.
➔ Rules
◆ Comments cannot appear before XML declaration.
◆ Comments may appear anywhere in a document.
◆ Comments must not appear within attribute values.
◆ Comments cannot be nested inside the other comments.
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8. XML - Comments (cond…)
➔ Example
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XML - Character
Entities
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9. XML - Character Entities
➔ There are some characters or symbols which are not available to be typed
directly from the keyboard or reserved for their use, which cannot be used
as content in XML code. Character Entities can be used to display those
symbols/special characters.
➔ Types of Character Entities
◆ Predefined Character Entities
◆ Numbered Character Entities
◆ Named Character Entities
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XML - CDATA
Sections
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10. XML - CDATA Sections
➔ The term CDATA means, Character Data.
➔ CDATA is defined as blocks of text that are not parsed by the parser, but
are otherwise recognized as markup.
➔ The predefined entities such as &lt;, &gt;, and &amp; require typing and
are generally difficult to read in the markup. In such cases, CDATA
section can be used.
➔ By using CDATA section, we are commanding the parser that the
particular section of the document contains no markup and should be
treated as regular text.
➔ Rules
◆ CDATA cannot contain the string "]]>" anywhere in the XML document.
◆ Nesting is not allowed in CDATA section.
➔ Example
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XML - WhiteSpaces
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11. XML - WhiteSpaces
➔ Whitespace is a collection of spaces, tabs, and newlines. They are
generally used to make a document more readable.
➔ XML document contains two types of whitespaces -
◆ Significant Whitespace
● A significant Whitespace occurs within the element which contains text and markup
present together.
◆ Insignificant Whitespace.
● Insignificant whitespace means the space where only element content is allowed.
➔ A special attribute named xml:space may be attached to an element. This
indicates that whitespace should not be removed for that element by the
application. We can set this attribute to default or preserve.
◆ The value default signals that the default whitespace processing modes of an application
are acceptable for this element.
◆ The value preserve indicates the application to preserve all the whitespaces.
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XML - Processing
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12. XML - Processing
➔ Processing instructions (PIs) allow documents to contain instructions for
applications. PIs are not part of the character data of the document, but
MUST be passed through to the application.
➔ Processing instructions (PIs) can be used to pass information to
applications. PIs can appear anywhere in the document outside the
markup. They can appear in the prolog, including the document type
definition (DTD), in textual content, or after the document.
➔ Syntax
➔ Example
◆ Here, the target is xml-stylesheet. href="tutorialspointstyle.css" and type="text/css" are
data or instructions the target application will use at the time of processing the given XML
document.
◆ In this case, a browser recognizes the target by indicating that the XML should be
transformed before being shown; the first attribute states that the type of the transform is
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XML - Encoding
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13. XML - Encoding
➔ Encoding is the process of converting unicode characters into their
equivalent binary representation.
➔ When the XML processor reads an XML document, it encodes the
document depending on the type of encoding. Hence, we need to specify
the type of encoding in the XML declaration.
➔ Encoding Types
● UTF-8
● UTF-16
◆ UTF stands for UCS Transformation Format, and UCS itself means Universal Character
Set.
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XML - Validation
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14. XML - Validation
➔ Validation is a process by which an XML document is validated. An XML
document is said to be valid if its contents match with the elements,
attributes and associated document type declaration(DTD), and if the
document complies with the constraints expressed in it.
➔ Validation is dealt in two ways by the XML parser. They are −
◆ Well-formed XML document
● A well-formed document in XML is a document that "adheres to the syntax rules
specified by the XML 1.0 specification in that it must satisfy both physical and
logical structures"
◆ Valid XML document
● If an XML document is well-formed and has an associated Document Type
Declaration (DTD), then it is said to be a valid XML document.
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XML - DTDs
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15. XML - DTDs
➔ 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.
➔ Syntax
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15. XML - DTDs
◆ 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.
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XML - Schemas
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16. XML - Schemas
➔ XML Schema is commonly known as XML Schema Definition (XSD).
➔ It is used to describe and validate the structure and the content of XML
data.
➔ XML schema defines the elements, attributes and data types.
➔ Schema element supports Namespaces.
➔ It is similar to a database schema that describes the data in a database.
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XML - Tree
Structure
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17. XML - Tree Structure
➔ An XML document is always descriptive. The tree structure is often
referred to as XML Tree and plays an important role to describe any XML
document easily.
➔ The tree structure contains root (parent) elements, child elements and so
on. By using tree structure, we can get to know all succeeding branches
and sub-branches starting from the root. The parsing starts at the root,
then moves down the first branch to an element, take the first branch
from there, and so on to the leaf nodes.
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17. XML - Tree Structure
➔ Example
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XML - DOM
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18. XML - DOM
➔ The Document Object Model (DOM) is the foundation of XML. XML
documents have a hierarchy of informational units called nodes; DOM is a
way of describing those nodes and the relationships between them.
➔ A DOM document is a collection of nodes or pieces of information
organized in a hierarchy. This hierarchy allows a developer to navigate
through the tree looking for specific information. Because it is based on a
hierarchy of information, the DOM is said to be tree based.
➔ The XML DOM, on the other hand, also provides an API that allows a
developer to add, edit, move, or remove nodes in the tree at any point in
order to create an application.
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XML - Namespaces
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19. XML - Namespaces
➔ A Namespace is a set of unique names. Namespace is a mechanisms by
which element and attribute name can be assigned to a group. The
Namespace is identified by URI(Uniform Resource Identifiers).
➔ Namespace Declaration
◆ The Namespace starts with the keyword xmlns.
◆ The word name is the Namespace prefix.
◆ The URL is the Namespace identifier.
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XML - Databases
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20. XML - Databases
➔ XML Database is used to store huge amount of information in the XML
format. As the use of XML is increasing in every field, it is required to
have a secured place to store the XML documents. The data stored in the
database can be queried using XQuery, serialized, and exported into a
desired format.
➔ There are two major types of XML databases −
◆ XML- enabled
● XML enabled database is nothing but the extension provided for the conversion of
XML document.
◆ Native XML (NXD)
● Native XML database is based on the container rather than table format. It can store
large amount of XML document and data. Native XML database is queried by the
XPath-expressions.
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XML - Viewers
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21. XML - Viewers
➔ An XML document can be viewed using a simple text editor or any
browser.
➔ Most of the major browsers supports XML. XML files can be opened in the
browser by just double-clicking the XML document (if it is a local file) or
by typing the URL path in the address bar (if the file is located on the
server), in the same way as we open other files in the browser.
➔ XML files are saved with a ".xml" extension.
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XML - Editors
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22. XML - Editors
➔ XML Editor is a markup language editor. The XML documents can be
edited or created using existing editors such as Notepad, WordPad, or any
similar text editor.
➔ Open Source XML Editors
◆ Online XML Editor
◆ Xerlin
◆ CAM - Content Assembly Mechanism
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XML - Parsers
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23. XML - Parsers
➔ XML parser is a software library or a package that provides interface for
client applications to work with XML documents. It checks for proper
format of the XML document and may also validate the XML documents.
Modern day browsers have built-in XML parsers.
➔ Following diagram shows how XML parser interacts with XML document
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XML - Processors
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24. XML - Processors
➔ When a software program reads an XML document and takes actions
accordingly, this is called processing the XML.
➔ Any program that can read and process XML documents is known as an
XML processor.
➔ An XML processor reads the XML file and turns it into in-memory
structures that the rest of the program can access.
➔ The most fundamental XML processor reads an XML document and
converts it into an internal representation for other programs or
subroutines to use.
➔ This is called a parser, and it is an important component of every XML
processing program.
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