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    Introduction To XML

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    Swapnil Patel
    This document provides an introduction to XML (eXtensible Markup Language). It describes XML as a markup language that uses tags to provide extra information about a document. The document discusses how XML is used to transfer data between places, its advantages over other formats, basic XML rules and syntax, and differences between XML and HTML. It provides examples of XML and HTML code.

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    Introduction To XML

    Uploaded by

    Swapnil Patel
    451 views35 pages
    This document provides an introduction to XML (eXtensible Markup Language). It describes XML as a markup language that uses tags to provide extra information about a document. The document discusses how XML is used to transfer data between places, its advantages over other formats, basic XML rules and syntax, and differences between XML and HTML. It provides examples of XML and HTML code.

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    This document provides an introduction to XML (eXtensible Markup Language). It describes XML as a markup language that uses tags to provide extra information about a document. The document discusses how XML is used to transfer data between places, its advantages over other formats, basic XML rules and syntax, and differences between XML and HTML. It provides examples of XML and HTML code.

    Copyright:

    © All Rights Reserved
    Download as PPT, PDF, TXT or read online from Scribd
    Download as ppt, pdf, or txt
    451 views35 pages

    Introduction To XML

    Uploaded by

    Swapnil Patel
    This document provides an introduction to XML (eXtensible Markup Language). It describes XML as a markup language that uses tags to provide extra information about a document. The document discusses how XML is used to transfer data between places, its advantages over other formats, basic XML rules and syntax, and differences between XML and HTML. It provides examples of XML and HTML code.

    Copyright:

    © All Rights Reserved
    Download as PPT, PDF, TXT or read online from Scribd
    Download as ppt, pdf, or txt
    of 35

    Introduction to XML

    Extensible Markup Language


    What is XML

    • 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?
    • 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

    • 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 of an HTML Document

    <html>
    <head><title>Example</title></head.
    <body>
    <h1>This is an example of a page.</h1>
    <h2>Some information goes here.</h2>
    </body>
    </html>
    Example of an XML Document

    <?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>
    Difference Between HTML and XML

    • 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
    and data.
    XML Rules

    • 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
    • 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
    • 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
    • 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.
    • A well-formed XML document is a document that conforms to the
    XML syntax rules, like:
    • it must begin with the XML declaration
    • it must have one unique root element
    • start-tags must have matching end-tags
    • elements are case sensitive
    • all elements must be closed
    • all elements must be properly nested
    • all attribute values must be quoted
    • entities must be used for special characters
    XML Example Revisited
    <?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>
    • Markup for the data aids understanding of its purpose.
    • A flat text file is not nearly so clear.
    Alice Lee
    alee@aol.com
    212-346-1234
    1985-03-22
    • The last line looks like a date, but what is it for?
    Expanded Example
    <?xml version = “1.0” ?>
    <address>
    <name>
    <first>Alice</first>
    <last>Lee</last>
    </name>
    <email>alee@aol.com</email>
    <phone>123-45-6789</phone>
    <birthday>
    <year>1983</year>
    <month>07</month>
    <day>15</day>
    </birthday>
    </address>
    XML Files are Trees

    address

    name email phone birthday

    first last year month day


    XML Trees

    • 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.
    XML Attributes
    • Attribute values must always be quoted.
    Either single or double quotes can be
    used.
    • For a student's gender, the <student>
    element can be written as:
    • <student gender="female">
    XML Elements vs. Attributes
    • <student gender="female">
    <firstname>Abc</firstname>
    <lastname>Pqr</lastname>
    </student >
    • OR
    <student >
    <gender>female</gender>
    <firstname>Abc</firstname>
    <lastname>Pqr</lastname>
    </student>
    • Both examples provide the same information.
    • There are no rules about when to use attributes or
    when to use elements in XML.
    Some things to consider when using
    attributes are:
    • attributes cannot contain multiple values
    (elements can)
    • attributes cannot contain tree structures
    (elements can)
    • attributes are not easily expandable (for
    future changes)
    XML Namespaces
    • XML Namespaces provide a method to
    avoid element 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.
    Validity
    • Use our XML validator to syntax-check your
    XML. With XML, errors are not allowed.
    • An XML document with correct syntax is called
    "Well Formed". 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.
    Valid XML Documents
    • A "well formed" XML document is not the same as a
    "valid" XML document.
    • A "valid" XML document must be well formed. In
    addition, it must conform to a document type
    definition/ Schema.
    • There are two different document type definitions that
    can be used with XML:
    • DTD - The original Document Type Definition
    • XML Schema - An XML-based alternative to DTD
    • A document type definition defines the rules and the
    legal elements and attributes for an XML document.
    XML DTD- Document Type Definitions
    • An XML document with correct syntax is called "Well
    Formed".
    • An XML document validated against a DTD is both
    "Well Formed" and "Valid".
    • 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
    <!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

    • 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.
    Schema for First address Example
    <?xml version="1.0" encoding="ISO-8859-1" ?>
    <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:element name="address">
    <xs:complexType>
    <xs:sequence>
    <xs:element name="name" type="xs:string"/>
    <xs:element name="email" type="xs:string"/>
    <xs:element name="phone" type="xs:string"/>
    <xs:element name="birthday" type="xs:date"/>
    </xs:sequence>
    </xs:complexType>
    </xs:element>
    </xs:schema>
    Explanation of Example Schema
    <?xml version="1.0" encoding="ISO-8859-1" ?>
    • ISO-8859-1, Latin-1, is the same as UTF-8 in the first 128 characters.
    <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
    • www.w3.org/2001/XMLSchema contains the schema standards.
    <xs:element name="address">
    <xs:complexType>
    • This states that address is a complex type element.
    <xs:sequence>
    • This states that the following elements form a sequence and must
    come in the order shown.
    <xs:element name="name" type="xs:string"/>
    • This says that the element, name, must be a string.
    <xs:element name="birthday" type="xs:date"/>
    • This states that the element, birthday, is a date. Dates are always of
    the form yyyy-mm-dd.
    XML Schemas are More
    Powerful than DTD
    • XML Schemas are written in XML
    • XML Schemas are extensible to additions
    • XML Schemas support data types
    • XML Schemas support namespaces
    Why Use an XML Schema?
    • With XML Schema, your XML files can
    carry a description of its own format.
    • With XML Schema, independent groups of
    people can agree on a standard for
    interchanging data.
    • With XML Schema, you can verify data.
    XML Schemas Support Data
    Types
    • One of the greatest strengths of XML
    Schemas is the support for data types:
    • It is easier to describe document content
    • It is easier to define restrictions on data
    • It is easier to validate the correctness of
    data
    • It is easier to convert data between
    different data types
    XML Schemas use XML Syntax
    • Another great strength about XML
    Schemas is that they are written in XML:
    • You don't have to learn a new language
    • You can use your XML editor to edit your
    Schema files
    • You can use your XML parser to parse
    your Schema files
    • You can manipulate your Schemas with
    the XML DOM
    • You can transform your Schemas with
    XSLT
    When to Use a DTD/Schema?
    • With a DTD, independent groups of people
    can agree to use a standard DTD for
    interchanging data.
    • With a DTD, you can verify that the data
    you receive from the outside world is valid.
    • You can also use a DTD to verify your own
    data.
    When NOT to Use a
    DTD/Schema?
    • XML does not require a DTD/Schema.
    • When you are experimenting with XML, or
    when you are working with small XML
    files, creating DTDs may be a waste of
    time.
    • If you develop applications, wait until the
    specification is stable before you add a
    document definition. Otherwise, your
    software might stop working because of
    validation errors.
    Parsers

    • 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
    XML DOM
    • The XML DOM makes a tree-structure
    view for an XML document.
    • We can access all elements through the
    DOM tree.
    • We can modify or delete their content and
    also create new elements. The elements,
    their content (text and attributes) are all
    known as nodes.
    • According to the XML DOM, everything in
    an XML document is a node:
    • The entire document is a document node
    • Every XML element is an element node
    • The text in the XML elements are text
    nodes
    • Every attribute is an attribute node
    • Comments are comment nodes
    •

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