EXTENSIBLE MARKUP LANGUAGE BY SAIKIRAN PANJALA

PRESENTING BY
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UNDER THE GUIDANCE OF
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EXTENSIBLE MARKUP
LANGUAGE

ABSTRACT
EXTENSIBLE MARKUP LANGUAGE
2
 Extensible Markup Language (xml) is a simple markup
language for describing the structure of document .it has been
derived from the Standard Generalized Markup Language
(SGML) for large-scale electronic publishing. it is also used in
data exchange on web. Unlike HTML and other presentation
languages, XML does not display data but carry and store data.
Thus, XML is easy to implement.

EXTENSIBLE MARKUP LANGUAGE 3
• XML has set of rules for creating other markup languages
.Thus , it may be referred as “Meta-markup”. Once a
language is created using XML it can be manipulated by any
number of applications that are designed for specific set of
requirements . xml is a W3C recommendation the W3C is
responsible for releasing the XML versions .The latest version
of XML is XML2.0.

INTRODUCTION
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 XML stands for eXtensible Markup Language.
 A markup language is used to provide information about a
document.
 Tags are added to the document to provide the extra information.
 HTML tags tell a browser how to display the document.
 XML tags give a reader some idea what some of the data means.

What is xml used for
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 XML documents are used to transfer data from one place to
another often over the Internet.
 XML subsets are designed for particular applications.
 One is RSS (Rich Site Summary or Really Simple Syndication ).
It is used to send breaking news bulletins from one web site to
another.
 A number of fields have their own subsets. These include
chemistry, mathematics, and books publishing.
 Most of these subsets are registered with the W3Consortium and
are available for anyone’s use.

Advantages of XML
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 XML is text (Unicode) based.
 Takes up less space.
 Can be transmitted efficiently.
 One XML document can be displayed differently in different
media.
 Html, video, CD, DVD,
 You only have to change the XML document in order to change
all the rest.
 XML documents can be modularized. Parts can be reused.

Example for XML document
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<?xml version=“1.0”/>
<address>
<name>Alice Lee</name>
<email>alee@aol.com</email>
<phone>212-346-1234</phone>
<birthday>1985-03-22</birthday>
</address>

Differences between HTML and XML
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 HTML tags have a fixed meaning and browsers know what it
is.
 XML tags are different for different applications, and users
know what they mean.
 HTML tags are used for display.
 XML tags are used to describe documents

XML Rules
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 Tags are enclosed in angle brackets.
 Tags come in pairs with start-tags and end-tags.
 Tags must be properly nested.
 <name><email>…</name></email> is not allowed.
 <name><email>…</email><name> is.
 Tags that do not have end-tags must be terminated by a ‘/’.
 <br /> is an html example.

More XML Rules
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 Tags are case sensitive.
 <address> is not the same as <Address>
 XML in any combination of cases is not allowed as part of a tag.
 Tags may not contain ‘<‘ or ‘&’.
 Tags follow Java naming conventions, except that a single colon
and other characters are allowed. They must begin with a letter
and may not contain white space.
 Documents must have a single root tag that begins the document.

Encoding
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 XML (like Java) uses Unicode to encode characters.
 Unicode comes in many flavors. The most common one used
in the West is UTF-8.
 UTF-8 is a variable length code. Characters are encoded in 1
byte, 2 bytes, or 4 bytes.
 The first 128 characters in Unicode are ASCII.
 In UTF-8, the numbers between 128 and 255 code for some of
the more common characters used in western Europe, such as
ã, á, å, or ç.
 Two byte codes are used for some characters not listed in the
first 256 and some Asian ideographs.
 Four byte codes can handle any ideographs that are left.
 Those using non-western languages should investigate other
versions of Unicode.

Well-Formed Documents
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 An XML document is said to be well-formed if it follows all the
rules.
 An XML parser is used to check that all the rules have been
obeyed.
 Recent browsers such as Internet Explorer 5 and Netscape 7
come with XML parsers.
 Parsers are also available for free download over the Internet.
One is Xerces, from the Apache open-source project.
 Java 1.4 also supports an open-source parser

XML Trees
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 An XML document has a single root node.
 The tree is a general ordered tree.
 A parent node may have any number of children.
 Child nodes are ordered, and may have siblings.
 Preorder traversals are usually used for getting information out
of the tree.

Validity
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 A well-formed document has a tree structure and obeys all the
XML rules.
 A particular application may add more rules in either a DTD
(document type definition) or in a schema.
 Many specialized DTDs and schemas have been created to
describe particular areas.
 These range from disseminating news bulletins (RSS) to
chemical formulas.
 DTDs were developed first, so they are not as comprehensive
as schema.

Document Type Definitions
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 A DTD describes the tree structure of a document and
something about its data.
 There are two data types, PCDATA and CDATA.
 PCDATA is parsed character data.
 CDATA is character data, not usually parsed.
 A DTD determines how many times a node may appear, and
how child nodes are ordered.

DTD for address Example
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<!ELEMENT address (name, email, phone, birthday)>
<!ELEMENT name (first, last)>
<!ELEMENT first (#PCDATA)>
<!ELEMENT last (#PCDATA)>
<!ELEMENT email (#PCDATA)>
<!ELEMENT phone (#PCDATA)>
<!ELEMENT birthday (year, month, day)>
<!ELEMENT year (#PCDATA)>
<!ELEMENT month (#PCDATA)>
<!ELEMENT day (#PCDATA)>

Schemas
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 Schemas are themselves XML documents.
 They were standardized after DTDs and provide more
information about the document.
 They have a number of data types including string, decimal,
integer, boolean, date, and time.
 They divide elements into simple and complex types.
 They also determine the tree structure and how many children a
node may have.

Parsers
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 There are two principal models for parsers.
 SAX – Simple API for XML
 Uses a call-back method
 Similar to javax listeners
 DOM – Document Object Model
 Creates a parse tree
 Requires a tree traversal

References
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 Elliotte Rusty Harold, Processing XML with Java, Addison
Wesley, 2002.
 Elliotte Rusty Harold and Scott Means, XML Programming,
O’Reilly & Associates, Inc., 2002.

conclusion
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 XML has quickly become the data interchange medium
for large & small companies to do business
 Strong industry support
 Portable & maintainable code
 Cost-effective method for doing business
 Continuing push for eCommerce/eBusiness

EXTENSIBLE MARKUP LANGUAGE BY SAIKIRAN PANJALA

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