This document discusses the structure and components of an XML document. It explains that an XML document consists of elements, attributes, comments, processing instructions, and a document type declaration. It describes each of these components in detail, including their purpose and general syntax. The document type declaration identifies the document and can reference an internal or external DTD that defines the valid elements and attributes.

1. UNIT I INTRODUCTION TO XML
XML document structure – Well formed and valid
documents – Namespaces – DTD – XML Schema
– X-Files.

2. XML Document Structure
Including all sections of an XML document
helps to make for a well-structured XML document

3. XML Document Structure
• An XML document consists of a number of discrete components
• Not all the sections of an XML document may be necessary,
– But their inclusion helps to make for a well-structured XML document
• A well-structured XML document can
– Easily be transported between systems and devices

4. Major portions of an XML document
• The major portions of an XML document include the following:
– The XML declaration
– The Document Type Declaration (DTD)
– The element data
– The attribute data
– The character data or XML content

5. XML Declaration
• XML Declaration is a definite way of stating exactly
– What the document contains.
• XML document can optionally have an XML declaration
– It must be the first statement of the XML document
• XML declaration is a processing instruction of the form
<?xml ...?>

6. Components of XML Declaration
Component Meaning
<?xml Starts the beginning of the processing instruction
Version= “xxx” Describes the specific version of XML being used
standalone= “xxx” Defines whether documents are allowed to contain
external markup declarations
encoding= “xxx” Indicates the character encoding that the document uses.
The default is “US-ASCII” but can be set to any value
Example :

7. Document Type Declaration (DOCTYPE)
• DOCTYPE
– Gives a name to the XML content , and
– Provides a means to guarantee the document’s validity,
• Either by including or specifying a link to a Document Type Definition (DTD).
• DOCTYPE is optional in XML
• Valid XML documents must declare the document type to which they
comply

8. General Form of DOCTYPE
• General Forms of the Document Type Declarations
<!DOCTYPE NAME SYSTEM “file”>
<!DOCTYPE NAME [ ]>
<!DOCTYPE NAME SYSTEM “file” [ ]>
First form refers to
– A document that only allows use of an externally defined DTD subset.
Second declaration
– Only allows an internally defined subset within the document.
Last form provides
– A place for inclusion of an internally defined DTD subset b/w square brackets
while also making use of an external subset.

9. Example on DOCTYPE
• Example on First Forms
<!DOCTYPE shirt SYSTEM “shirt.dtd”>
– Root (first) tag in the document will be the <shirt> element
– DTD is saved to a file named shirt.dtd

10. Components of DOCTYPE

11. Markup and Content
• XML documents are composed of markup and content.
• In general, six kinds of markup can occur in an XML document:
– elements,
– entity references,
– comments,
– processing instructions,
– marked sections, and
– Document Type Declarations.

12. Elements
• XML elements are
– Either a matched pair of XML tags or single XML tags that are “self-closing.”
• For example,
– A shirt element begins with <shirt> and ends with </shirt>.
• When elements do not come in pairs,
– The element name is suffixed by the forward slash.
• The “unmatched” elements are known as empty elements
• Elements can be arbitrarily nested within other elements

13. Attributes
• Within elements,
Additional information can be communicated to XML processors
– That modifies the nature of the encapsulated content.
• Attributes are name/value pairs contained within the start element
– That can specify text strings that modify the context of the element.
• Example:
<price currency=”USD”>…</price>
<on_sale start_date=”10-15-2001”/>

14. Entity References
• Some characters have a special meaning in XML,
• Entity references indicate to XML-processing applications
– That a special text string is to follow that will be replaced with a different literal value,
• Entity references are delimited by
– An ampersand at the beginning and
– A semicolon at the ending.
• Ex : Inserting a > sign in our text
<descript> Following says 8 is greater than 5 </descript>
<equation>4 &gt; 5</equation>
Major Entity References Character
&lt; <
&gt; >
&amp; &
&quot; "
&apos; '

15. Comments
• Comments can be placed anywhere in a document and
– They are not considered to be part of the textual content of an XML document.
• Character sequence <!-- begins a comment and --> ends the comment.
• B/w these 2 delimiters,
– Any text at all can be written, including valid XML markup.
• Only restriction is that
– Comment delimiters cannot be used; neither can the literal string --.
• Example :
<!-- The below element talks about Elephant I once owned... -->
<animal>Elephant</animal>

16. Processing Instructions (PIs)
• PIs are not a textual part of an XML document
– But provide information to applications as to how the content should be processed.
• Unlike comments, XML processors are required to pass along PIs.
• Processing instructions have the following form:
<?instruction options?>
• Instruction name is called the PI target
– It is a special identifier that the processing application is intended to understand.
• Any following information can be optionally specified
• Example: <?send-message “process complete”?>

17. Marked CDATA Sections
• Some documents will contain a large number of characters and text
– That an XML processor should ignore and pass to an application.
• These are known as character data (or CDATA) sections.
• Within an XML document, a CDATA section instructs the parser
– To ignore all markup characters except the end of the CDATA markup instruction.
• This allows for a section of XML code to be “escaped”
– So that it doesn’t inadvertently disrupt XML processing.
• CDATA sections follow this general form:
<![CDATA[content]]>

18. Marked CDATA Sections
• All content contained in the CDATA section is
– Passed as string literals directly to the application without interpretation
• Example:
<object_code>
<![CDATA[
function master(poltice integer) {
if poltice<=3 then {
Mas=poltice+IntToString(FindElement(“<chicken>”));
}
}
]]>
</object_code>

19. Document Type Definitions (DTD)
• Don’t confuse the DOCTYPE with the DTD.
• A DOCTYPE and a DTD serve very different, although related purposes.
– DOCTYPE is used to identify and name the XML content
– DTD is used to validate the metadata contained within.
• DTDs represent a specific form of XML text
– That is allowable in an XML document.
• DTDs and XML Schema are the means for defining the validity constraints
on XML documents

20. XML Content
• XML content can consist of any data, including binary data,
– As long as it doesn’t violate rules that would confuse the content with valid XML
metadata instructions.
• XML content can contain any characters,
– Including any valid Unicode and international characters.
• XML content can be as long as necessary

22. XML document with an internal DTD
• A DTD defines the structure & the legal elements and attributes of an XML
document.
• An application can use a DTD to verify that XML data is valid.
• If the DTD is declared inside the XML file,
– It must be wrapped inside the <!DOCTYPE> definition.
• Document Type Declaration (DOCTYPE) gives a name to the XML
content

23. Document Type Declaration (DOCTYPE)
• A DTD defines the structure & the legal elements and attributes of an XML
document.
• An application can use a DTD to verify that XML data is valid.
• If the DTD is declared inside the XML file,
– It must be wrapped inside the <!DOCTYPE> definition.
• Document Type Declaration (DOCTYPE) gives a name to the XML
content