fundamentals of XML

XML Document Structure
• XML declaration
• Document type declaration
• Element data
• Attribute data
• Character data/XML content

Xml declaration
Components:
• <?xml
• Version=“1.0”
• Standalone =“yes/no”
• Encoding=“US-ASCII”

Document type declaration(DOCTYPE)
• Link to DTD
• General forms:
– <!DOCTYPE NAME SYSTEM “file”>
– <!DOCTYPE NAME []>
– <!DOCTYPE NAME SYSTEM “file” []>

Components
• <
• !DOCTYPE
• NAME
• SYSTEM
• “file”
• [
• ]
• >

Markup and content
Six kinds of markup in XML document:
• Elements
• Entity references
• Comments
• Processing instruction
• Marked section
• Document Type Definition

Elements
• A matched pair of XML tags
<shirt> ….. </shirt>
• Single XML tags with ‘self-closing’/empty
element
<shirt/>
• Nested elements

Rules for element name
• Element name can contain letters, numbers,
other characters
• No start with a number or punctuation character
• No white space inbetween words
<this_is_really_long_element_name>
• no name as xml or with colon
• Should be descriptive, not confusing.
• Avoid hyphen(-) and dot(.)

Attributes
• Additional information about element
• Eg:
<price currency=“USD”>….</price>
<on_sale start_date=“10.5.2001”/>
• In DTD, attribute can be required, optional, fixed
and enumerated.
• Eg:
<shirt><color>red</color></shirt>
Or <shirt color=“red”/>

Entity reference
• Symbols referred by name
• Starts with ampersand and ends with
semicolon.
• Eg: <element> 4 > 2</element>
• Types: internal entity & external entity

Comments & PI
• 
• PI(processing Instruction) same as comments.
• Information about how the content should be
processed.
• <?instruction options?>
• PI target
• Eg: <?send message “process completed”?>

Marked CDATA section
• Character data/CDATA section
• Instructs parser to ignore all markup like
elements, entity, PI,…
• All passed as string.
• <![CDATA[content]]>

DTD
• Validate the documents.
• Well defined rules for document structure and
content.

XML content
• Content between the elements
• Can consist any data
• Can be long ie.100MB

XML content model
• 3 types: open, closed & mixed.
• Open: can add elements & attributes without
declaration in DTD or XML schema.
• Closed: restricts elements and attributes to
only those that are specified in the DTD or
schema.
• Mixed

Handling whitespace
• Character spaces, tabs, linefeeds, and carriage
returns in documents.
• Whitespace is significant is by knowing the
content model of the XML document .
• Mixed-significant
• Open/closed-not significant
• Special attribute:- xml:space with 2
values:perserve/default

Rules of XML structure
Rule 1:All XML elements must have a closing tag.
Eg: <markup>This is not valid XML
<markup>Since there is no closing tag.
Rule 2:XML tags are case sensitive.
Eg: <Markup>These two tags are very
different</markup>

Rule 3:All XML Elements Must Have Proper
Nesting.
Eg:<oxygen><nitrogen>These tags are
improperly nested</oxygen></nitrogen>
Rule 4: All XML Documents Must Contain a
Single Root Element.

Rule 5:Attribute Values Must Be Quoted.
Eg:
<?xml version=1.0?>
<shirt>
<price currency=USD>14.99</price>
</shirt>

Rule 6:Attributes May Only Appear Once in the
Same Start Tag
Eg: shirt size=”large” size=”small”>Zippy Tee
</shirt>
Rule 7: Attribute Values Cannot Contain References
to External Entities
Rule 8:All Entities Except amp, lt, gt, apos, and quot
Must Be Declared Before They Are Used
Eg: & , <,>, ', &qout;

Well formed and valid document
• a valid XML document is a more strict form of
a well-formed XML document .
• well formed if it follows all the preceding
syntax rules of XML.
• valid XML documents can improve the quality
of document processes.

Linking XML document
• Xlink
• Xpointer

Namespace
• Method to avoid the name conflict.
• Namespaces use a colon-delimited prefix to
associate external semantics with elements
that can be identified via a Universal
Resource Identifier (URI).

Example
• <Customer>
<Name>John Smith</Name>
</Customer>
• <Product>
<Name>Hot Dog Buns</Name>
</Product>

Example
• <Customer>
<Name>John Smith</Name>
<Order>
<Product>
</Product>
</Order>
</Customer>

Example
• <Customer>
<cust:Name xmlns:cust=”customer-namespace-
URI”>John Smith</cust:Name>
<cust:Order>
<prod:Product xmlns:prod=”product-namespace-
URI”>
<prod:Name >Hot Dog Buns</prod:Name>
</prod:Product>
</cust:Order>
</cust:Customer>

Default namespace
• <Customer xmlns=”http://www.eps-
software.com/po”>
<Name>Travis Vandersypen</Name>
<Order>
<Product>
</Product>
</Order>
</Customer>

Example
• <po:Customer xmlns:po=”http://www.eps-
software.com/po”>
<po:Name>Travis Vandersypen</po:Name>
<po:Order>
<po:Product>
<po:Name>Hot Dog Buns</po:Name>
</po:Product>
</po:Order>
</po:Customer>

Multiple namespaces
<cust:Customer xmlns:cust=”http://www.eps-
software.com/customer”
xmlns:ord=”http://www.eps-software.com/order”>
<cust:Name>Travis Vandersypen</cust:Name>
<ord:Order>
<ord:Product>
<prod:Name xmlns:prod=”product-namespace-
URI”>Hot Dog Buns</ord:Name>
</ord:Product>
</ord:Order>
</cust:Customer>

Inheriting
<Customer xmlns=”http://www.eps-
software.com/customer”>
<Name>Travis Vandersypen</Name>
<Order xmlns=”http://www.eps-
software.com/order”>
<Product>
</Product>
</Order>
</Customer>

fundamentals of XML

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