XML Schema and Namespaces

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XML Schema and Namespaces
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XML Namespaces

• Solve the problem   Tag name conflicts
• XHTML   - HTML 4.0 written in XML
• MathML   - Display mathematics equations
• XHTML and MathML overlap   ,

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Why do we need namespaces?

• It is conceivable that several XML languages may
  want to use the same name for an element or
  attribute, e.g.
• The meaning of is different in each
  context
• Therefore we need some way of distinguishing
  between the two, Namespaces guarantee unique
  naming of XML elements and attributes

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Namespaces

• The W3C suggests the following
• Associate each XML language with a URI
• (e.g. www.xml.org)
• because each URI is unique
• A namespace is the collection of elements
  attributes associated with that URI
• The URI doesn't need to point to an actual web
  page!!!

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Namespaces . contd

• The mechanism introduces three new concepts to
  XML
• Namespace URI
• Prefix
• Qualified name

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Example
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Namespace URIs

• 0'
• Order
• .com'
• Large Oak
• 2.00 m
• 1.45 m
• xmlnsprefixURI

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Default Namespace

• Order
• m'
• Large Oak
• 2.00 m
• 1.45 m

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Prefixes

• '
• Order
• m'
• Large Oak
• 2.00 m
• 1.45 m
• hx is the prefix bound to the html namespace
• fx is the prefix bound to the furnitureML
• namespace

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Local Names

• html, table, tr, td
• furniture, table
• '
• Order
• '
• Large Oak
• 2.00 m
• 1.45 m

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Qualified Names

• qName prefixlocalName
• hxhtml, hxtable, hxtr, hxtd
• fxfurniture, fxtable
• '
• Order
• '
• Large Oak
• 2.00 m
• 1.45 m

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Scope

• A Namespace comes into scope on the element it is
  declared and remains in scope until that element
  closes
• It is in scope for all of children of that
  element
• Unless the prefix associated with that namespace
  is (temporarily) overridden by another namespace
• An overridden namespace comes back into scope
  when the one over-ridding it goes out of scope

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Scope

• /core

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Scope

• e
• 20
• 0.54
• jon
• xxxx
• 
  
• 1
• ...
• n

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Scope

• xmlnshttp//www.xml-cml.org/schema/cml2/core
• xmlnsbhttp//www.w3.org/TR/MathML2/
• 20
• 0.54
• jon
• xxxx
• 1
• ...
• n

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Review

• Namespaces
• A collection of attribute and element names
  associated with some URI
• Namespace URI
• xmlnsprefixuri
• Default Namespace
• xmlnsuri
• Scope
• Namespace scope

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Review .... contd
prefix
Local name

• l2/core/

Namespace URI
Qualified name
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XML Schemas

• Schemas is a general term--DTDs are a form of
  XML schemas
• According to the dictionary, a schema is a
  structured framework or plan
• When we say XML Schemas, we usually mean the
  W3C XML Schema Language
• This is also known as XML Schema Definition
  language, or XSD
• Ill use XSD frequently, because its short
• DTDs, and XML Schemas are all XML schema languages

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Why XML Schemas?

• DTDs provide a very weak specification language
• You cant put any restrictions on text content
• You have very little control over mixed content
  (text plus elements)
• You have little control over ordering of elements
• DTDs are written in a strange (non-XML) format
• You need separate parsers for DTDs and XML
• The XML Schema Definition language solves these
  problems
• XSD gives you much more control over structure
  and content
• XSD is written in XML

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Why not XML schemas?

• DTDs have been around longer than XSD
• Therefore they are more widely used
• Also, more tools support them
• XSD is very verbose, even by XML standards
• More advanced XML Schema instructions can be
  non-intuitive and confusing
• Nevertheless, XSD is not likely to go away quickly

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The XSD document

• The file extension is .xsd
• The root element is
• The XSD starts like this
• xmlnsxs"http//www.w3.rg/2001/XMLSchema"

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• The element may have attributes
• xmlnsxs"http//www.w3.org/2001/XMLSchema"
• This is necessary to specify where all our XSD
  tags are defined
• elementFormDefault"qualified"
• This means that all XML elements must be
  qualified (use a namespace)
• It is highly desirable to qualify all elements,
  or problems will arise when another schema is
  added

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XML Schema

• To define a "class" of XML Documents
• "instance document" - XML document that conforms
  to a particular schema
• W3C XML Shema Specification
• XML Schema Part 0 Primerhttp//www.w3.org/TR/xml
  schema-0/
• XML Schema Part 1 Structures"to express
  syntactic, structural and value constraints
  applicable to its document instances"http//www.w
  3.org/TR/xmlschema-1/
• XML Schema Part 2 Datatypes"higher degree of
  type checking to ensure robustness in document
  understanding and data interchange"http//www.w3.
  org/TR/xmlschema-2/

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Complete Example

• Document
• John Punin
• puninj_at_cs.rpi.edu
• Harrison Ford hford_at_famou
  s.org
• Julia Roberts
• jr_at_pw.com

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Complete Example (2)

• DTD

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Complete Example (3)

• XML Schema
• Schema"
• minOccurs"0 maxOccurs"unbounded"/

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Parts of XML Schema Document

• Root element schema element
• Schema" ...

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Parts of XML Schema Document (2)

• Named Types
• Simple Type - only values
• John Punin
• Complex Type - elements and/or attributes
• John Punin
• puninj_at_cs.rpi.edu
• 
  

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Simple and complex elements

• A simple element is one that contains text and
  nothing else
• A simple element cannot have attributes
• A simple element cannot contain other elements
• A simple element cannot be empty
• However, the text can be of many different types,
  and may have various restrictions applied to it
• If an element isnt simple, its complex
• A complex element may have attributes
• A complex element may be empty, or it may contain
  text, other elements, or both text and other
  elements

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Defining a simple element

• A simple element is defined as name"name" type"type" /where
• name is the name of the element
• the most common values for type are
  xsboolean xsinteger xsdate xsstring
  xsdecimal xstime
• Other attributes a simple element may have
• default"default value if no other value is
  specified
• fixed"value" no other value may be specified

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Simple Types

• string - "Programming XML in Java"
• integer - 32, -45
• decimal - 12.4, -2.3
• float - 12.4, 3.6E-5, INF, NaN
• boolean - true, false
• time - 152300.000-0400
• date - 2001-02-18
• ID - same as in DTD
• NMTOKEN - same as in DTD

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Simple Type Examples

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Simple Type Examples (2)

• Derived type'
• Using the enumeration facetname"myWeek"
• .....
  

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Restrictions, or facets

• The general form for putting a restriction on a
  text value is
• (or
  xsattribute)
  ... the restrictions ...
  
• For example
• base"xsinteger"
  value"0"
  value"140"

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Restrictions on numbers

• minInclusive -- number must be the given value
• minExclusive -- number must be the given value
• maxInclusive -- number must be the given value
• maxExclusive -- number must be
• totalDigits -- number must have exactly value
  digits
• fractionDigits -- number must have no more than
  value digits after the decimal point

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Restrictions on strings

• length -- the string must contain exactly value
  characters
• minLength -- the string must contain at least
  value characters
• maxLength -- the string must contain no more than
  value characters
• pattern -- the value is a regular expression that
  the string must match
• whiteSpace -- not really a restriction--tells
  what to do with whitespace
• value"preserve" Keep all whitespace
• value"replace" Change all whitespace
  characters to spaces
• value"collapse" Remove leading and trailing
  whitespace, and replace all sequences of
  whitespace with a single space

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Enumeration

• An enumeration restricts the value to be one of a
  fixed set of values
• Example
• 
  
  
  
  
  
  
  
  nt

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Complex elements

• A complex element is defined as name"name"
  ... information about the complex type...
  
• Example
  
  type"xsstring" / name"lastName" type"xsstring" /
  
  
• says that elements must occur in
  this order
• Remember that attributes are always simple types

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Complex Types

• (title?,firstname,lastname)
• maxOccurs"unbounded"/

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Complex Types (2)

• Derived Type by Extension(title?, firstname,
  lastname, genMark?)
• 
  

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Complex Types (3)

• Derived Type by Restriction(firstname,
  lastname)
  

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A Simple Example

• DTD
• XML Schema
• ref"name"/
• use"required"/
• XML Document
• The deadline of homework 1 is
  Nov 10 2006

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xssequence

• Weve already seen an example of a complex type
  whose elements must occur in a specific order
• sequencetype"xsstring" /type"xsstring" /e

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xsall

• xsall allows elements to appear in any order
• alltype"xsstring" /type"xsstring" /
  
• Despite the name, the members of an xsall group
  can occur once or not at all
• You can use minOccurs"0" to specify that an
  element is optional (default value is 1)
• In this context, maxOccurs is always 1

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Referencing

• Once you have defined an element or attribute
  (with name"..."), you can refer to it with
  ref"..."
• Example
• all
  type"xsstring" /
  type"xsstring" /
  xselement
• Or just

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Compositors

• Sequence
• (title?,firstname,lastname)
• maxOccurs"unbounded"/

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Compositors (2)

• Choice
• (PRODUCT, NUMBER, (PRICE CHARGEACCT SAMPLE))

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Groups

• (PRODUCT, NUMBER, (PRICE CHARGEACCT SAMPLE))

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Elements

• Elements with Simple typesname"cname" type"xsdstring"/
• Elements with Anonymous Complex types
• Elements with Named Complex typese name"record"

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References to Elements

• DTD
• XML Schema
• maxOccurs"unbounded"/

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Attributes and Complex Types from Simple Types

• DTD
• XML Schema
• type"xsdstring"/
• XML Instance Documentlanguage"Spanish" Hola!

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Empty Content

• icon"/

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Empty elements

• Empty elements are (ridiculously) complex
• 
  base"xsanyType"/ name"count" type"xsinteger"/
  

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Text element with attributes

• If a text element has attributes, it is no longer
  a simple type
• xssimpleContent
  base"xsinteger"
  type"xsinteger"
  ent

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Mixed elements

• Mixed elements may contain both text and elements
• We add mixed"true" to the xscomplexType element
• The text itself is not mentioned in the element,
  and may go anywhere (it is basically ignored)
• 
  name"someName
  type"xsanyType"/ xType

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Extensions

• You can base a complex type on another complex
  type
• 
  base"otherType" ...new stuff...
  
  

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Predefined date and time types

• xsdate -- A date in the format CCYY-MM-DD, for
  example, 2002-11-05
• xstime -- A date in the format hhmmss (hours,
  minutes, seconds)
• xsdateTime -- Format is CCYY-MM-DDThhmmss
• The T is part of the syntax
• Allowable restrictions on dates and times
• enumeration, minInclusive, minExclusive,
  maxInclusive, maxExclusive, pattern, whiteSpace

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Global and local definitions

• Elements declared at the top level of a
  are available for use throughout the
  schema
• Elements declared within a xscomplexType are
  local to that type
• Thus, inypetype"xsstring" /type"xsstring" /eelements firstName and lastName
  are only locally declared
• The order of declarations at the top level of a
  do not specify the order in the XML data
  document

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Declaration and use

• So far weve been talking about how to declare
  types, not how to use them
• To use a type we have declared, use it as the
  value of type"..."
• Examples
• Scope is important you cannot use a type if is
  local to some other type

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Defining an attribute

• Attributes themselves are always declared as
  simple types
• An attribute is defined as name"name" type"type" /where name and type
  are the same as for xselement
• Other attributes a simple element may have
• default"default valueif no other value is
  specified
• fixed"value no other value may be specified
• use"optional the attribute is not required
  (default)
• use"required the attribute must be present

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Attribute Groups

• DTD
• src CDATA REQUIRED
• width CDATA IMPLIED
• height CDATA IMPLIED
• XML Schema
• use"required"/
• use"required"/
• 
  
•