Xml Presentation-3

What is XML?
 a meta language that allows you to
create and format your own
document markups
 a method for putting structured data
into a text file; these files are
- easy to read
- unambiguous
- extensible
- platform-independent

What is XML?
 a family of technologies:
- XML 1.0
- Xlink
- Xpointer & Xfragments
- CSS, XSL, XSLT
- DOM
- XML Namespaces
- XML Schemas

XML Facts
 officially recommended by W3C
since 1998
 a simplified form of SGML (Standard
Generalized Markup Language)
 primarily created by Jon Bosak of
Sun Microsystems

XML Facts
 important because it removes two
constraints which were holding
back Web developments:
1. dependence on a single, inflexible
document type (HTML);
2. the complexity of full SGML, whose
syntax allows many powerful but
hard-to-program options

Quick Comparison
 HTML
- uses tags and
attributes
- content and formatting
can be placed
together
<p><font=”Arial”>text</font>
- tags and attributes are
pre-determined and
rigid
 XML
- uses tags and
attributes
- content and format are
separate; formatting
is contained in a
stylesheet
- allows user to specify
what each tag and
attribute means

Importance of being able to
define tags and attributes
 document types can be explicitly
tailored to an audience
 the linking abilities are more
powerful
- bidirectional and multi-way link
- link to a span of text, not just a single
point

The pieces
 there are 3 components for XML
content:
- the XML document
- DTD (Document Type Declaration)
- XSL (Extensible Stylesheet Language)
 The DTD and XSL do not need to be
present in all cases

A well-formed XML
document
 elements have an open and close tag,
unless it is an empty element
 attribute values are quoted
 if a tag is an empty element, it has a
closing / before the end of the tag
 open and close tags are nested correctly
 there are no isolated mark-up characters
in the text (i.e. < > & ]]>)
 if there is no DTD, all attributes are of
type CDATA by default

A valid XML document
 has an associated DTD and complies
with the constraints in the DTD

XML basics
 <?xml ?> the XML declaration
- not required, but typically used
- attributes include:
version
encoding – the character encoding used in
the document
standalone –if an external DTD is required
<?xml version=”1.0” encoding=”UTF-8”>
<?xml version=”1.0” standalone=”yes”>

XML basics
 <!DOCTYPE …> to specify a DTD
for the document
2 forms:
<!DOCTYPE root-element SYSTEM “URIofDTD”>
<!DOCTYPE root-element PUBLIC “name”
“URIofDTD”>

XML basics
  comments
- contents are ignored by the processor
- cannot come before the XML declaration
- cannot appear inside an element tag
- may not include double hyphens

XML basics
 <tag> text </tag> an element
- can contain text, other elements or a
combination
- element name:
-must start with a letter or underscore and
can have any number of letters, numbers,
hyphens, periods, or underscores
- case-sensitive;
- may not start with xml

XML basics
Elements (continued)
 can be a parent, grandparent,
grandchild, ancestor, or descendant
 each element tag can be divided
into 2 parts – namespace:tag name

XML basics
 Namespaces:
- not mandatory, but useful in giving
uniqueness to an element
- help avoid element collision
- declared using the xmlns:name=value
attribute; a URI is recommended for
value
- can be an attribute of any element; the
scope is inside the element’s tags

XML basics
 Namespaces (continued):
- may define more than 1 per element
- if no name given after xmlns prefix,
uses the default namespace which is
applied to all elements in the defining
element without their own namespace
- can set default namespace to an empty
string to ensure no default namespace is
in use within an element

XML basics
 key=”value” an attribute
- describes additional information about
an element
<tag key=”value”> text</tag>
- value must always be quoted
- key names have same restrictions as
element names
- reserved attributes are
- xml:lang
- xml:space

XML basics
 <tag></tag> OR <tag/> empty
element
- has no text
- used to add nontextual content or to
provide additional information to parser
 <? ?> processing instruction
- for attributes specific to an outside
application

XML basics
 <![CDATA[ ]]>
- to define special sections of character
data which the processor does not
interpret as markup
- anything inside is treated as plain text

Xml Presentation-3

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