XSD: XML Schema Language

1
XSD XML Schema Language

• Kanda Runapongsa
• (krunapon_at_kku.ac.th)
• Dept. of Computer Engineering
• Khon Kaen University

2
XML Schema DTD

• Like a DTD, its purpose is to define the legal
  building blocks of an XML document
• defines elements that can appear in a document
• defines attributes that can appear in a document
• defines which elements are child elements

3
XML Schema DTD (Cont.)

• defines the order of child elements
• defines the number of child elements
• defines whether an element is empty or can
  include text
• defines data types for elements and attributes
• defines default and fixed values for elements and
  attributes

4
Advantages of XSD over DTD

• XML Schemas use XML syntax
• Do not need to learn a new syntax
• Use any XML parser to parse XML schemas
• XML Schemas support many data types and allow you
  to create new data types
• No Integer or Double types in DTD

5
Adv. of XSD over DTD (Cont.)

• XML Schemas allow you to group elements to
  control the recurrence of elements and attributes
• In DTD, we cannot specify that the number of
  occurrences of elements must be at least 2 and at
  most 5
• XML Schemas support namespaces

6
The ltschemagt Element

• The ltschemagt element is the root element of every
  XML Schema
• lt?xml version"1.0"?gt
• ltxsschemagt
• ...
• ...
• lt/xsschemagt

7
The ltschemagt Element (Cont.)

• lt?xml version"1.0"?gt
• ltxsschema xmlnsxs"http//www.w3.org/2001/XMLSch
  ema" targetNamespace"http//abc.com"
  xmlnshttp//abc.com" elementFormDefault"qualifi
  ed"gt
• ...
• ...
• lt/xsschemagt

8
Attributes of ltSchemagt

• xmlnsxshttp//www.w3.org/2001/XMLSchema
• Indicates that the elements and data types used
  in the schema (schema, element,) come from the
  http//www.w3.org/2001/XMLSchema namespace
• These elements and data types should be prefixed
  with xs

9
Attributes of ltSchemagt (Cont.)

• targetNamespacehttp//abc.com
• Indicates that the elements defined by this
  schema (Note, To, From,..) is in the
  "http//www.w3schools.com" namespace

10
Attributes of ltSchemagt (Cont.)

• xmlnshttp//abc.com
• Indicates that the default namespace is
  http//abc.com
• elementFormDefault"qualified
• indicates that any elements used by the XML
  instance document which were declared in this
  schema must be namespace qualified.

11
XSD Simple Elements

• A simple element
• Can contain only text
• Cannot contain any other elements
• Cannot contain any attributes
• Can text be any other types besides string?
• It can be date, etc., or even a custom type that
  you can define yourself

12
Defining a Simple Element

• The syntax for defining a simple element is
• ltxselement name"xxx" type"yyy"/gt
• where xxx is the name of the element and yyy is
  the data type of the element.

13
Simple Elements Example

• Some XML elements
• ltlastnamegtWaseelt/lastnamegt
• ltagegt34lt/agegt
• Corresponding element definitions
• ltxselement namelastname typexsstring/gt
• ltxselement nameage typexsinteger/gt

14
Built-in Data Types

• xsstring
• xsdecimal
• xsinteger
• xsboolean
• xsdate
• xstime

15
Simple Elements Default Values

• Simple elements can have a default value
• A default value is automatically assigned to the
  element when no value is specified
• ltxselement nameTo typexsstring
  defaultstudents/gt

16
Simple Elements Fixed Values

• A fixed value is automatically assigned to
  elements
• We cannot specify another value
• ltxselement nameTo typexsstring
  fixedstudents/gt

17
XSD Attributes

• All attributes are declared as simple types
• Only complex elements can have attributes
• An element with attributes always has a complex
  type definition

18
Defining an Attribute

• Syntax
• ltxsattribute namexxx typeyyy/gt
• Where xxx is the name of the attribute and yyy is
  the data type of the attribute
• Examples
• XMLltlname langENgtDeelt/namegt
• XSDltxsattribute namelang typexsstring/gt

19
Default Fixed Values for Attributes

• Attributes can have a default value or a fixed
  value specified
• Examples
• ltxsattribute namelang typexsstring
  defaultEN/gt
• ltxsattribute namelang typexsstring
  fixedEN/gt

20
Optional Required Attributes

• All attributes are optional by default
• To explicitly specify that the attribute is
  optional or required, use the use attribute
• Examples
• ltxsattribute namelang typexsstring
  useoptional/gt
• ltxsattribute namelang typexsstring
  userequired/gt

21
Restrictions on Content

• When an XML element or attribute has a type
  defined, it puts a restriction for the elements
  or attributes content
• We can also add our own restrictions to our XML
  elements and attributes
• These restrictions are called facets

22
XSD Restrictions/Facets

• Restrictions are used to control acceptable
  values for XML elements or attributes
• Many kinds of restrictions/facets
• Restrictions on values
• Restrictions on white spaces
• Restrictions on length

23
Restrictions on Values

• This example defines an element called age with
  a restriction.
• ltxselement nameagegt
• ltxssimpleTypegt
• ltxsrestriction basexsintegergt
• ltxsminInclusive value0/gt
• ltxsmaxInclusive value60/gt
• lt/xselementgt
• What range the value of age is in?
• Cannot be lower than 0 or greater than 60

24
Restriction on a Set of Values

• To limit the content of an XML element to a set
  of acceptable values, we would use the
  enumeration constraint
• ltxselement namegradegt
• ltxssimpleTypegt
• ltxsrestriction basexsstringgt
• ltxsenumeration valueA/gt
• ltxsenumeration valueB/gt
• lt/xselementgt

25
Restrictions on a Series of Values

• To limit the content to a series of numbers or
  letters, use the pattern constraint
• ltxselement namelettergt
• ltxssimpleTypegt
• ltxsrestriction basexsstringgt
• ltxspattern valuea-z/gt
• lt/xselementgt
• What are the acceptable values of the letter
  element?

26
Restrictions on a Series of Values

• ltxselement name"letter"gt
• ltxssimpleTypegt
• ltxsrestriction base"xsstring"gt ltxspattern
  value"(a-zA-Z)"/gt
• lt/xselementgt
• What are the acceptable values of the letter
  element?

27
Restrictions on a Series of Values

• ltxselement name"passwordgt
• ltxssimpleTypegt
• ltxsrestriction base"xsstring"gt ltxspattern
  value"a-zA-Z0-98"/gt
• ltxselementgt
• What are the acceptable values of the password
  element?

28
Restrictions on White Space Characters

• To specify how white space characters should be
  handled, use the whiteSpace constraint
• ltxselement name"address"gt
• ltxssimpleTypegt
• ltxsrestriction base"xsstring"gt
  ltxswhiteSpace value"preserve"/gt
• lt/xselement
• The XML processor will not remove any white space
  characters

29
Restrictions on White Space Characters

• Three values of whiteSpace
• preserve the XML processor will not remove any
  white space characters
• replace the XML processor will replace all white
  space characters with spaces
• collapse the XML processor will remove all white
  space characters (leading and trailing spaces are
  removed)

30
Restrictions on Length

• ltxselement name"password"gt
• ltxssimpleTypegt
• ltxsrestriction base"xsstring"gt ltxslength
  value"8"/gt
• lt/xselementgt
• Can we specify the minimum and maximum length of
  the value?
• Yes, use minLength and maxLength

31
What is a Complex Element?

• A complex element is an XML element that contains
  other elements and/or attributes
• Four kinds of complex elements
• Empty elements
• Elements that contain only other elements
• Elements that contain only text
• Elements that contain both other elements and text

32
Complex Elements

• Ex1 ltproduct pid1345/gt
• Ex2 ltagtltbgt1lt/bgtltcgt2lt/cgtlt/agt
• Ex3 ltfood typedessertgtIce creamlt/foodgt
• Ex4 ltdescriptiongtToday is ltdategt11.13.2003lt/dategt
  lt/descriptiongt

33
Defining a Complex Element

• ltxselement nameemployeegt
• ltxscomplexTypegt
• ltxssequencegt
• ltxselement namefirstname
  typexsstring/gt
• ltxselement namelastname typexsstring/gt
• lt/xselementgt

34
Sharing the Element Type

• ltxselement nameemployee typepersoninfo/gt
• ltxselement namestudent typepersoninfo/gt
• ltxscomplexType namepersoninfogt
• ltxssequencegt
• ltxselement namefirstname
• lt/xselementgt

35
Defining Based on Other Types

• ltxselement name"employee" type"fullpersoninfo"/
  gt
• ltxscomplexType name"personinfo"gt
• lt/xscomplexTypegt
• ltxscomplexType name"fullpersoninfo"gt
  ltxscomplexContentgt
• ltxsextension base"personinfo"gt
• ltxssequencegt
• ltxselement name"address" type"xsstring
  "/gt
• lt/xscomplexTypegt

36
Types for Empty Elements

• XML ltproduct prodid"1345" /gt
• XSD
• ltxselement name"product" type"prodtype"/gt
• ltxscomplexType name"prodtype"gt ltxsattribute
  name"prodid" type"xspositiveInteger"/gt
• lt/xscomplexTypegt

37
Elements w/ Only Sub-Elements

• XMLltpgtltfngtAlt/fngtltlngtBlt/lngtlt/pgt
• XSD
• ltxselement name"p" type"persontype"/gt
• ltxscomplexType name"persontype"gt ltxssequencegt
• ltxselement name"fn" type"xsstring"/gt
• ltxselement name"ln" type"xsstring"/gt
• lt/xssequencegt
• lt/xscomplexTypegt

38
Elements w/ Only Text

• XML ltshoesizegt8lt/shoesizegt
• XSD
• ltxselement name"shoesize" type"shoetype"/gt
• ltxscomplexType name"shoetype"gt
  ltxssimpleContentgt
• ltxsextension base"xsinteger"gt
• lt/xscomplexTypegt

39
Types w/ Mixed Content

• XML ltlettergtToday is ltdategt11.13.2003lt/dategtlt/let
  tergt
• XSD
• ltxselement name"letter"gt
• ltxscomplexType mixed"true"gt
• ltxssequencegt
• ltxselement name"shipdate" type"xsdate"/gt
• lt/xselementgt

40
Indicators

• Order indicators
• All, choice, sequence
• Occurrence indicators
• maxOccurs, minOccurs
• Group indicators
• Group name
• attributeGroup name

41
All Indicator

• Specify by default that the child elements can
  appear in any order and each child element must
  occur once and only once
• ltxselement namepersongt
• ltxscomplexTypegt
• ltxsallgt
• ltxselement namefname
• typexsstring/gt
• lt/xselementgt

42
Choice Indicator

• Specify that either one child element or another
  can occur
• ltxselement name"person"gt ltxscomplexTypegt
• ltxschoicegt
• ltxselement name"employee" type"employee"/
  gt
• ltxselement name"member" type"member"/gt
• ...
• lt/xselementgt

43
Sequence Indicator

• Specify that the child elements must appear in a
  specific order
• ltxselement name"paper"gt ltxscomplexTypegt
• ltxssequencegt
• ltxselement nameabstract" type"xsstring
  "/gt
• ltxselement nameintroduction"
  type"xsstring"/gt
• lt/xselementgt

44
Occurrence Indicator

• Define how often an element can occur
• maxOccurs Indicator maximum number of times an
  element can occur
• ltxselement name"person"gt
• ltxscomplexTypegt
• ltxssequencegt
• ltxselement name"full_name"
  type"xsstring"/gt
• ltxselement name"child_name"
  type"xsstring" maxOccurs"10"/gt
• lt/xselementgt

45
Occurrence Indicator (Cont.)

• minOccurs Indicator minimum number of times an
  element can occur
• ltxselement name"person"gt
• ltxscomplexTypegt
• ltxssequencegt
• ltxselement name"full_name"
  type"xsstring"/gt
• ltxselement name"child_name"
  type"xsstring" maxOccurs"10
  minOccurs0/gt
• lt/xselementgt

46
Group Indicators

• Define related sets of elements
• Element Groups are defined with the group
  declaration, like this
• ltxsgroup namegroupnamegt
• lt/xsgroupgt
• After defining a group, we can reference it in
  another complex type definition

47
Element Groups

• ltxsgroup name"persongroup"gt
• ltxssequencegt
• ltxselement name"firstname" type"xsstring"/gt
  
• lt/xsgroupgt
• ltxscomplexType name"personinfo"gt ltxssequencegt
• ltxsgroup ref"persongroup"/gt
• ltxselement name"country" type"xsstring"/gt

48
Attribute Groups

• ltxsattributeGroup name"personattrgroup"gt
  ltxsattribute name"firstname" type"xsstring"/gt
• lt/xsattributeGroupgt
• ltxselement name"person"gt
• ltxscomplexTypegt
• ltxsattributeGroup ref"personattrgroup"/gt
• lt/xselementgt