XML Schema Definition (XSD) Explained

XML Schema
Mani Bushan D’souza
mail2mani@email.com

Topics Covered
What is Schema
How to use the XML Schema language in
applications

What is it?
An XML Schema defines the legal structure that an
XML document may take, much like a blueprint.
This is accomplished by:
defining elements and child elements
defining attributes
defining the order of child elements
defining element content
defining data types for elements and attributes
defining default and fixed values

Definition and Declaration
Definition
 Create new types (both simple and complex
types)
Declaration
 Enable elements and attributes with specific
names and types (both simple and complex) to
appear in document instances

Schema vs. DTD
Schemas are extensible.
Schemas have more depth and power.
Schemas are written in XML.
Schemas support data types.
Schemas support namespaces.

Document Type Definition
An Information Modeling Syntax
a
b
x
y
DTD
“a is the parent of b.
x and y are children of b.”
<a>

<x>…</x>
<y>…</y>

</a>
Enforces
Structure
x and y are always interpreted as
String, regardless of how they are used
Schema vs. DTD

XML Schema
Information Modeling Syntax in XML
a
b
x
y
XML
Schema
<a>

<x>…</x>
<y>…</y>

</a>
Enforces
Structure
<xsl:element name=“x” type=“boolean” />
<xsl:attribute name=“z” type=“integer” />
x and y now have
enforceable data types
Schema vs. DTD

Comparing Element Declarations
Differences in data typing and syntax
DTD <!ELEMENT Age (#PCDATA)>
XML Schema <element name=“Age” type=“integer”/>
XML <Age>2009</Age>

Why Support Data Types?
Easier to describe allowable document
content.
Easier to validate data.
Easier to work with data from a database.
Easier to define data restrictions.
Easier to define data formats.
Easier to convert data between types.

Schema Validation
Schemas can be used to validate a document in two ways:
Content Model Validation
Checks order and nesting of elements (similar to DTD validation)
DataType Validation
Checks the element content for valid type and range
example: month element is an integer between 1 and 12
<month>5</month> VALID!!
<month>15</month> INVALID!!

Comparison with DTDs
DTDs use their own unique syntax (SGML)
XML Schema uses XML syntax
DTDs are concise
XML Schema is verbose

XML Schema can be parsed and manipulated programmatically like
any other XML document
DTDs cannot
(at least not without a bit of work)
Note: Custom DTD parsers are available, but the ability to parse a DTD is not inherent in
most XML Parsers.
XML Schema enforce Data Typing
DTDs cannot
(DTDs see everything as Strings)

XML Schema allows open-ended data models
 Vocabulary extension and inheritance
DTDs support only a closed model
XML Schema supports attribute groups
 DTDs offer only limited attribute group support

Schemas are Extensible
 Reuse Schemas in other Schemas.
 Create proprietary data types from public types.
 Reference multiple Schemas in one document.

XML Schema supports namespace
integration
 Allows the association of individual nodes of a
document with type declarations in a schema
DTDs allow only one association (between
the document and the DTD)

Multiple levels of checking
BookCatalogue.xml BookCatalogue1.xsd xml-schema.dtd
Does the xml document
conform to the rules laid
out in the xml-schema?
Is the xml-schema a valid
xml document, i.e., does it
conform to the rules laid
out in the xml-schema DTD?

Schema Features
Rich Datatypes ( integers, time, date, boolean.. )
User-defined types
Extendable types
Open, closed or refinable content models
open: Additional elements may appear
refinable: Additional elements may appear if they are defined in the schema
Grouping
Namespace support

Schemas v. DTDs
Schemas DTDs
Support namespaces n/a
Written in XML syntax n/a
Full, object-oriented extensibility
Very limited
Extensive datatype support
Extended via
string substitutions
Open, closed or refinable
content models Closed only

End of DTDs?
DTDs have:
Widespread use and support
Many legacy applications, documents
Too much time & money invested
Experienced programmers/consultants
There is a DTD to define XML Schema

Benefits of XML and Schemas
You don’t need to learn a new language.
Editor of choice will work on Schemas.
Current parser will work on Schemas.
You can manipulate your Schema with the
XML DOM.
Schemas are transformable with XSLT.

Schema Workflow
XML Document
Normalized
XML Document
Schema
Error message
Schema
Processor
Valid
Invalid

XSD (XML Schema Definition) How To
Look at this simple XML document called "note.xml":
 <?xml version="1.0"?>
<note>
<to>Tom</to>
<from>Jerry</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>
This is a simple DTD file called "note.dtd" that defines the
elements of the XML document above ("note.xml"):
 <!ELEMENT note (to, from, heading, body)>
<!ELEMENT to (#PCDATA)>
<!ELEMENT from (#PCDATA)>
<!ELEMENT heading (#PCDATA)>
<!ELEMENT body (#PCDATA)>

Simple XML schema
<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.aimit.com"
xmlns="http://www.aimit.com"
elementFormDefault="qualified">
<xsd:element name="note">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="to" type="xsd:string"/>
<xsd:element name="from" type="xsd:string"/>
<xsd:element name="heading" type="xsd:string"/>
<xsd:element name="body" type="xsd:string"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:schema>

The <schema> element
The <schema> is the root element of every XML schema
<xsd:schema>
...
...
</xsd:schema>
The <schema> element may contain some attributes. A
schema declaration often looks something like this:
... ... </xsd:schema>
The schema element must specify the namespace for
schemas as its xmlns:xsd attribute

XML <schema> element explained
xmlns:xsd="http://www.w3.org/2001/XMLSchema”
 indicates that the elements and data types used in the schema (schema,
element, complexType, sequence, string, boolean, etc.) come from the
"http://www.w3.org/2001/XMLSchema" namespace.
 It also specifies that the elements and data types that come from the
"http://www.w3.org/2001/XMLSchema" namespace should be prefixed
with xsd:
 indicates that the elements defined by this schema (note, to, from, heading,
body.) come from the "http://www.aimit.com" namespace.
 indicates that the default namespace is "http://www.aimit.com".
elementFormDefault="qualified"
 indicates that any elements used by the XML instance document which were
declared in this schema must be namespace qualified.

The XSD document
Since the XSD is written in XML, it can get confusing, what
we are talking about (XML or XSD?)
The file extension is .xsd
The root element is <schema>
The XSD starts like this:
 <?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.rg/2001/XMLSchema">

targetNamespace="http://www.books.org"
xmlns="http://www.books.org"
<xsd:element name="BookStore">
<xsd:complexType>
<xsd:sequence>
<xsd:element ref="Book" minOccurs="1" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:element name="Book">
<xsd:complexType>
<xsd:sequence>
<xsd:element ref="Title" minOccurs="1" maxOccurs="1"/>
<xsd:element ref="Author" minOccurs="1" maxOccurs="1"/>
<xsd:element ref="Date" minOccurs="1" maxOccurs="1"/>
<xsd:element ref="ISBN" minOccurs="1" maxOccurs="1"/>
<xsd:element ref="Publisher" minOccurs="1" maxOccurs="1"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:element name="Title" type="xsd:string"/>
<xsd:element name="Author" type="xsd:string"/>
<xsd:element name="Date" type="xsd:string"/>
<xsd:element name="ISBN" type="xsd:string"/>
<xsd:element name="Publisher" type="xsd:string"/>
</xsd:schema>
BookStore.xsd
xsd = Xml-Schema Definition

<xsd:complexType>
<xsd:sequence>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:complexType>
<xsd:sequence>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:schema>
<!ELEMENT Title (#PCDATA)>
<!ELEMENT Author (#PCDATA)>
<!ELEMENT Date (#PCDATA)>
<!ELEMENT ISBN (#PCDATA)>
<!ELEMENT Publisher (#PCDATA)>
<!ELEMENT Book (Title, Author, Date,
ISBN, Publisher)>
<!ELEMENT BookStore (Book+)>

<xsd:complexType>
<xsd:sequence>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:complexType>
<xsd:sequence>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:schema>
All XML Schemas have
"schema" as the root
element.

<xsd:complexType>
<xsd:sequence>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:complexType>
<xsd:sequence>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:schema>
The elements and
datatypes that
are used to construct
schemas
- schema
- element
- complexType
- sequence
- string
come from the
http://…/XMLSchema
namespace

element
complexType
schema
sequence
http://www.w3.org/2001/XMLSchema
XMLSchema Namespace
string
integer
boolean

<xsd:complexType>
<xsd:sequence>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:complexType>
<xsd:sequence>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:schema>
Says that the
elements defined
by this schema
- BookStore
- Book
- Title
- Author
- Date
- ISBN
- Publisher
are to go in this
namespace

BookStore
Book
Title
Author
Date
ISBN
Publisher
http://www.books.org (targetNamespace)
Book Namespace (targetNamespace)

<xsd:complexType>
<xsd:sequence>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:complexType>
<xsd:sequence>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:schema>
This is referencing a
Book element declaration.
The Book is in which
namespace?
Since there
is no namespace qualifier
it is referencing the Book
element in the default
namespace, which is the
targetNamespace! Thus,
this is a reference to the
Book element declaration
in this schema.
The default namespace is
http://www.books.org
which is the
targetNamespace!

<xsd:complexType>
<xsd:sequence>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:complexType>
<xsd:sequence>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:schema>
This is a directive to any
instance documents which
conform to this schema:
Any elements that are
defined in this schema
must be
namespace-qualified
when used in instance
documents.

Other Attributes
Attribute Description
id Optional. Creates an unique ID for the element.
attributeFormDefault Optional. The form for attributes declared in target name space
of the schema. Must be either “qualified” or “unqualified”
elementFormDefault Optional. The form for elements declared in the target name
space of the schema. Must either be “qualified” or “unqualified”
blockDefault Optional. Specifies the default value of the block attribute on
element and complexType elements in namespace.
finalDefault Optional. Specifies the default value of the final attribute on
element, simpleType, and complexType elements in the
namespace.
targetNamespace Optional. An URI ref to the namespace of this schema.
version Optional. Specifies the version of the schema.
xmlns A URI ref specifying one or more namespaces for the schema.
any attributes Optional. Specifies other attributes with non-schema
namespace.

Referencing a schema in an XML instance
document
<BookStore xmlns ="http://www.books.org"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.books.org
BookStore.xsd">
<Book>
<Title>My Life and Times</Title>
<Author>Paul McCartney</Author>
<Date>July, 1998</Date>
<ISBN>94303-12021-43892</ISBN>
<Publisher>McMillan Publishing</Publisher>
</Book>
...
</BookStore>
1. First, using a default namespace declaration, tell the schema-validator that all of the elements
used in this instance document come from the http://www.books.org namespace.
2. Second, with schemaLocation tell the schema-validator that the http://www.books.org
namespace is defined by BookStore.xsd (i.e., schemaLocation contains a pair of values).
3. Third, tell the schema-validator that the schemaLocation attribute we are using is the one in
the XML Schema-instance namespace.
1
2
3

schemaLocation
type
noNamespaceSchemaLocation
http://www.w3.org/2001/XMLSchema-instance
XMLSchema-instance Namespace
nil

Referencing a schema in an XML
instance document
BookStore.xml BookStore.xsd
schemaLocation="http://www.books.org
BookStore.xsd"
- defines elements in
namespace http://www.books.org
- uses elements from
namespace http://www.books.org
A schema defines a new vocabulary. Instance documents use that new vocabulary.

A Reference to a DTD - Comparison
<!DOCTYPE note SYSTEM "http://www.aimit.com/dtd/note.dtd">
<note>
<to>Tom</to>
<from>Jerry</from>
</note>

A Reference to an XML Schema …
<note xmlns="http://www.aimit.com"
xsi:schemaLocation="http://www.aimit.com note.xsd">
<to>Tom</to>
<from>Jerry</from>
</note>

A Reference to an XML Schema
 specifies the default namespace declaration. This declaration tells the
schema-validator that all the elements used in this XML document are
declared in the "http://www.aimit.com" namespace.
 XML Schema Instance namespace
 The XML Schema Instance reference is required
xsi:schemaLocation="http://www.aimit.com note.xsd"
 this schemaLocation attribute has two values. The first value is the
namespace to use. The second value is the location of the XML
schema to use for that namespace

Cross-Referencing XML with Schemas
File “Person.xml” File “Person.xsd”
<?xml version="1.0"
encoding="UTF-8"?>
<Person
xmlns:xsi="http://www.w3.org/
2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="
Person.xsd">
<First>Katrina</First>
<Last>Khaif</Last>
<Age>24</Age>
</Person>
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema
xmlns:xs="http://www.w3.org/2001/
XMLSchema">
<xs:element name="Person">
<xs:complexType> <xs:sequence>
<xs:element name="First“
type="xs:string"/>
<xs:element name="Middle“
type="xs:string“
minOccurs="0"/>
<xs:element name="Last“
type="xs:string"/>
<xs:element name="Age“
type="xs:integer"/>
</xs:sequence> </xs:complexType>
</xs:element>
</xs:schema>

Qualify XMLSchema,
Default targetNamespace
In the first example, we explicitly qualified all elements from the
XML Schema namespace. The targetNamespace was the default
namespace.
BookStore
Book
Title
Author
Date
ISBN
Publisher
element
complexType
schema
sequence
string
integer
boolean

Default XMLSchema,
Qualify targetNamespace
• Alternatively (equivalently), we can design our schema so that
XMLSchema is the default namespace.
BookStore
Book
Title
Author
Date
ISBN
Publisher
element
complexType
schema
sequence
string
integer
boolean

<schema xmlns="http://www.w3.org/2001/XMLSchema"
xmlns:bk="http://www.books.org"
<element name="BookStore">
<complexType>
<sequence>
<element ref="bk:Book" maxOccurs="unbounded"/>
</sequence>
</complexType>
</element>
<element name="Book">
<complexType>
<sequence>
<element ref="bk:Title"/>
<element ref="bk:Author"/>
<element ref="bk:Date"/>
<element ref="bk:ISBN"/>
<element ref="bk:Publisher"/>
</sequence>
</complexType>
</element>
<element name="Title" type="string"/>
<element name="Author" type="string"/>
<element name="Date" type="string"/>
<element name="ISBN" type="string"/>
<element name="Publisher" type="string"/>
</schema>
Note that
http://…/XMLSchema
is the default
namespace.
Consequently, there
are no namespace
qualifiers on
- schema
- element
- complexType
- sequence
- string

<schema xmlns="http://www.w3.org/2001/XMLSchema"
xmlns:bk="http://www.books.org"
<element name="BookStore">
<complexType>
<sequence>
<element ref="bk:Book" minOccurs="1" maxOccurs="unbounded"/>
</sequence>
</complexType>
</element>
<element name="Book">
<complexType>
<sequence>
<element ref="bk:Title"/>
<element ref="bk:Author"/>
<element ref="bk:Date"/>
<element ref="bk:ISBN"/>
<element ref="bk:Publisher"/>
</sequence>
</complexType>
</element>
<element name="Title" type="string"/>
<element name="Author" type="string"/>
<element name="Date" type="string"/>
<element name="ISBN" type="string"/>
<element name="Publisher" type="string"/>
</schema>
Here we are
referencing a
Book element.
Where is that
Book element
defined? In
which namespace?
The bk: prefix
indicates what
namespace this
element is in. bk:
has been set to
be the same as the
targetNamespace.

"bk:" References the targetNamespace
BookStore
Book
Title
Author
Date
ISBN
Publisher
bk
element
complexType
schema
sequence
string
integer
boolean
Consequently, bk:Book refers to the Book element in the targetNamespace.

XML Abstract Data Model
The XML Abstract Data Model
 composes of Schema Components.
 is used to describe XML Schemas.
Schema Component
 is the generic term for the building blocks that
compose the abstract data model of the schema.

13 Kinds of Schema Components
Simple type definitions
Complex type definitions
Attribute declarations
Element declarations
Attribute group definitions
Identity-constraint definitions
Model group definitions
Notation declarations
 Annotations
 Model groups
 Particles
 Wildcards
 Attribute Uses
Secondary
Primary
Helper

Relationships among Schema Components
Identity-
constraint
Definitions
Element
Declaration
Attribute
Declaration
Notation
Declaration
Simple Type
Definition
Complex Type
Definition
Particle
WildCard Model Group
AttributeUse
Attribute group
definition
Model group
definition
Information
Item
type
Conform
to
type
type
use
type
constrain
reference
reference

Primary Schema Components
XML Namespaces
Element Declarations
Attribute Declarations
Simple Type Definitions
Complex Type Definitions

XML Schema
(.xsd)
XML document & XML Schema
Information
Items
…
Elements
Attributes
XML Document
(.xml)

Declaration & Definition
Declaration Components
 are associated by (qualified) names to information
items being validated.
 It is like declaring objects in OOP.
Definition Components
 define internal schema components that can be used
in other schema components.
 Type definition is like defining classes in OOP.

Definitions vs. Declarations
A definition describes a
complex or simple type that
either contains element or
attribute declarations or
references element or attribute
declarations defined elsewhere
in the document.
Here’s a definition:
<xsd:complexType name=”bookType”>
<xsd:sequence>
<xsd:element name=”title”
type=”xsd:string”/>
<xsd:element name=”author”
<xsd:element name=”description”
</xsd:sequence>
</xsd:complexType>
A declaration defines an
element or attribute, specifying
the name and datatype for the
component.
Here’s a declaration:
<xsd:element name=”book”>
<xsd:complexType>
<xsd:sequence>
<xsd:element name=”title”
<xsd:element name=”author”
<xsd:element name=”description”
</xsd:sequence>
</xsd:complexType>
</xsd:element>

Consider XML Instance Document Example
<book isbn="0-7356-1465-2">
<title> XML Step by Step</title>
<author> Michael young</author>
<publisher> Microsoft press</publisher>
</book>

Examples
<xs:element name="book">
<xs:complexType>
<xs:sequence>
<xs:element name="title" type="xs:string"/>
… …
</xs:sequence>
<xs:attribute name="isbn" type="xs:string"/>
</xs:complexType>
</xs:element>
<xs:complexType name="bookType">
<xs:sequence>
<xs:element name="title" type="nameType"/>
… …
</xs:sequence>
<xs:attribute name="isbn" type="isbnType" use="required"/>
</xs:complexType>
Declaration
Type Definition <xs:element name="book" type="bookType"/>
<book isbn="0-7356-1465-2">
<title>
XML Step by Step
</title>
……
</book>

Declaration vs. Definition
Declarations
 Enable elements and attributes with specific names and
types (both simple and complex) to appear in document
instances.
<xsd:element name="purchaseOrder" type="PurchaseOrderType"/>
<xsd:element name="comment" type="xsd:string"/>
Definitions
 create new types (both simple and complex)
<xsd:complexType name="PurchaseOrderType">
<xsd:sequence>
<xsd:element name="shipTo" type="Address"/>
<xsd:element name="billTo" type="Address"/>
<xsd:element ref="comment" minOccurs="0"/>
<xsd:element name="items" type="Items"/>
</xsd:sequence>
<xsd:attribute name="orderDate" type="xsd:date"/>
</xsd:complexType>

Type Definitions
Why Type Definitions?
Simple Type Definition VS. Complex Type Definition
Attributes & Elements without
element children
Complex Type
Definition
Simple Type
Definition
Elements

“Simple” and “Complex” elements
A “simple” element is one that contains text and
nothing else
 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 isn’t simple, it’s “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

Defining a simple element
A simple element is defined as
<xs:element name="name" type="type" />
where:
 name is the name of the element
 the most common values for type are
xs:boolean xs:integer
xs:date xs:string
xs:decimal xs:time
Other attributes a simple element may have:
 default="default value" if no other value is specified
 fixed="value" no other value may be specified

Examples of Simple element
using Built-in Simple Types
<xsd:element name=“weight” type=“xsd:string”/>
<xsd:element name=“population” type=“xsd:integer” />

Simple Elements
Example:
 <lastname>Amir Khan</lastname>
 <age>35</age>
 <dateborn>1975-09-15</dateborn>
 Corresponding simple element definition:
 <xs:element name="lastname" type="xs:string"/>
 <xs:element name="age" type="xs:integer"/>
 <xs:element name="dateborn" type="xs:date"/>

Declare Default and Fixed Values for Simple Elements
Simple elements can have a default value OR a fixed value
set.
A default value is automatically assigned to the element
when no other value is specified. In the following example
the default value is "red":
 <xs:element name="color" type="xs:string" default="red"/>
A fixed value is also automatically assigned to the element.
You cannot specify another value. In the following example
the fixed value is "red":
 <xs:element name="color" type="xs:string" fixed="red"/>

Primitive Type
XML Schema has a complex system of types.
Different types may describe:
1. the allowed values of attributes,
2. the allowed content of elements, or
3. the allowed content and the allowed attributes of
elements.
There is a subset of types, called the simple
types, that can be used in either of the first
two roles.

Simple Types
Built-in simple type Description Example(s)
xsd:string A sequence of any of
the legal XML characters
This is a string.
xsd:boolean
The value true or false, or 1 or
0 (indicating true or false,
respectively)
true
false
1
0
xsd:decimal A number that may contain a
decimal component
-5.2
-3.0
1
2.5
xsd:integer A whole number -389
-7
0
5
229

Simple Types
xsd:positivelnteger A positive whole number(not
including 0)
5
229
xsd:negativelnteger
A negative whole number (not
including 0)
-389
-7
xsd:date
A calendar date, represented as
CCYY-MM-DD
1948-05-21
2001-10-15

Simple Types
Built-in
simple type
Description Example(s)
xsd:time A time of day, represented
as hh:mm:ss.ss
11:30:00.00(11:30 A.M.)
14:29:03 (2:29 P.M. and 3
seconds)
05:16:00.0(5:16 A.M.)
xsd:dateTime A date and time of day,
represented as
CCYY-MM-DDThh:mm:ss.ss
1948-05-21T17:28:00.00
xsd:gMonth A Gregorian calendar
month, represented as
-MM-
-05- (May)
-12- (December)
xsd:gYear A Gregorian calendar year,
represented as CCYY
1948
2001

Simple Types
xsd:gDay A day of a Gregorian
calendar month,
represented as -DD
-05
-31
xsd:gYearMonth A Gregorian calendar
year and month,
represented as
CCYY-MM
1948-05 (May, 1948)
xsd:anyURI A URI (Uniform Resource
Identifier).
http://www.myOnline.com

Examples of Built-in Simple Types
<element name=“Title” type=“string”/>
<element name=“Heading” type=“string”/>
<element name=“Topic” type=“string”/>
<element name=“Price” type=“decimal”/>

XSD Complex Elements
A complex element contains other elements
and/or attributes.
● empty elements
● elements that contain only other elements
● elements that contain only text
● elements that contain both other elements and text
<employee>
<firstname>Mani</firstname>
<lastname>Dsouza</lastname>
</employee>

Example of complex elements
A complex XML element, "product", which is empty:
<product pid="1345"/>
A complex XML element, "employee", which contains only other elements:
<employee>
<firstname>Salman</firstname>
<lastname>Khan</lastname>
</employee>
A complex XML element, "food", which contains only text:
<food type=“Vanilla">Ice cream</food>
A complex XML element, "description", which contains both elements and
text:
<description>
It happened on <date lang="norwegian">03.03.99</date> ....
</description

How to Define a Complex Element
Complex XML element:
<employee>
<firstname>Mani</firstname>
<lastname>Dsouza</lastname>
</employee>
XSD:
<xs:element name="employee">
<xs:complexType>
<xs:sequence>
<xs:element name="firstname" type="xs:string"/>
<xs:element name="lastname" type="xs:string"/>
</xs:sequence>
</xs:complexType>
</xs:element>

Complex Element Example 1
<xsd:element name="Address" >
<xsd:complexType >
<xsd:sequence>
<xsd:element name="name" type="xsd:string" />
<xsd:element name="street" type="xsd:string" />
<xsd:element name="city" type="xsd:string" />
<xsd:element name="state" type="xsd:string" />
<xsd:element name="zip" type="xsd:decimal" />
</xsd:sequence>
<xsd:attribute name="country" type="xsd:NMTOKEN"
use="fixed" value="IN"/>
</xsd:complexType>
<xsd:element>

Elements can be declared in two ways
<xsd:element name="name" type="type" minOccurs="int" maxOccurs="int"/>
A simple type
(e.g., xsd:string)
or the name of
a complexType
(e.g., BookPublication)
<xsd:element name="name" minOccurs="int" maxOccurs="int">
<xsd:complexType>
…
</xsd:complexType>
</xsd:element>
1
2
A nonnegative
integer
A nonnegative
integer or "unbounded"
Note: minOccurs and maxOccurs can only
be used in nested (local) element declarations.

Note that:
<xsd:element name="A" type="xyz"/>
<xsd:complexType name="xyz">
<xsd:sequence>
<xsd:element name="B" …/>
<xsd:element name="C" …/>
</xsd:sequence>
</xsd:complexType>
is equivalent to:
<xsd:element name="A">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="B" …/>
<xsd:element name="C" …/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
Element A references the
complexType xyz.
Element A has the
complexType definition
inlined in the element
declaration.

Type Attribute or complexType Child
Element, but not Both!
An element declaration can have a type
attribute, or a complexType child element, but it
cannot have both a type attribute and a
complexType child element.
<xsd:element name="A" type="xyz">
<xsd:complexType>
…
</xsd:complexType>
</xsd:element>

Defining an attribute
Attributes are always declared as simple types
An attribute is defined as
<xs:attribute name="name" type="type" />
where:
 name and type are the same as for xs:element
Other attributes a simple element may have:
 default="default value" if no other value is specified
 fixed="value" no other value may be specified

Primary Schema Components
<xsd:attribute name=“size” type=“xsd:integer” default=“12”>
Attribute:
<xsd:attribute ref=“size” default=“12” use=“optional”>

Example: Attribute declaration
<element name=“StdRecord”>
<complexType>
<sequence>
<element name=“SName” type=“string”/>
<element name=“Course” type=“string”/>
<element name=“Gender” type=“token”/>
<element name=“DateOfBirth” type=“date”/>
</sequence>
<attribute name=“RegNo” type=“integer”/>
</complexType>
</element>
Instance Document
<Record RegNo=“420”>
<SName>Shakti Kapoor</SName>
<Course>MS</Course>
<Gender>M</Gender>
<DateOfBirth>1963-06-01</DateOfBirth>
</Record>

Attributes
Simple elements cannot have attributes.
If an element has attributes, it is considered to be of
complex type.
The attribute itself is always declared as a simple
type..
Example:
 An XML element with an attribute
 <lastname lang="EN">Khan</lastname>
 A corresponding simple attribute definition:
 <xs:attribute name="lang" type="xs:string"/>

Declare Default and Fixed Values for Attributes
Attributes can have a default value OR a fixed value specified
A default value is automatically assigned to the attribute
when no other value is specified. In the following example the
default value is "EN":
 <xs:attribute name="lang" type="xs:string" default="EN"/>
A fixed value is also automatically assigned to the attribute.
You cannot specify another value. In the following example
the fixed value is "EN":
 <xs:attribute name="lang" type="xs:string" fixed="EN"/>

XML Schema Types
Simple types
 Basic datatypes
 Can be used for attributes and element text
 Extendable
Complex types
 Defines structure of elements
 Extendable
Types can be named or “anonymous”

The Simple Type: <simpleType>
The Simplest Type Declaration:
 <simpleType name = “FirstName” type = “string”/>
Based on a primitive or the derived built-in datatypes
Cannot contain sub-elements or attributes
Can declare constraining properties (“facets”)
 minLength, maxLength, Length, etc
May be used as base type of a complexType

Simple Types
Simple Types are of three varieties:
 Atomic: Built-in or derived, e.g.
<xsd:simpleType name="myInteger">
<xsd:restriction base="xsd:integer">
<xsd:minInclusive value="10000"/>
<xsd:maxInclusive value="99999"/>
</xsd:restriction>
</xsd:simpleType>
 List: multiple items of the same type
<listOfMyInt>20003 15037 95977
95945</listOfMyInt>
 Union: Union or two or more Simple Types

XML Schema Datatypes
Two kinds of datatypes: Built-in and User-defined
Built-in
 Primitive Datatypes
 string, double, duration, etc
 Derived Datatypes:
 CDATA, integer, date, byte, etc
 Derived from the primitive types
 Example: integer is derived from decimal
User-defined
 Derived from built-in or other user-defined datatypes
 specify constraints on an existing type (the base type)
 Constraints are given in terms of facets
 totalDigits, maxInclusive, etc.

Built-in Datatypes
Primitive Datatypes
 string
 boolean
 decimal
 float
 double
 duration
 dateTime
 time
 date
 gYearMonth
 gYear
 gMonthDay
Atomic, built-in
 "Hello World"
 {true, false, 1, 0}
 7.08
 12.56E3, 12, 12560, 0, -0, INF, -INF, NAN
 12.56E3, 12, 12560, 0, -0, INF, -INF, NAN
 P1Y2M3DT10H30M12.3S
 format: CCYY-MM-DDThh:mm:ss
 format: hh:mm:ss.sss
 format: CCYY-MM-DD
 format: CCYY-MM
 format: CCYY
 format: --MM-DD
Note: 'T' is the date/time separator
INF = infinity
NAN = not-a-number

Date and Time Data Types
Code.xsd
<xsd:element name=“gestation”
type=“xsd:timeDuration”/>
(represent a certain amount of time)
Code.xml
<gestation>P3M15D</gestation>
(PnYnMnDTnHnMnS)
Period
n - non negative
T begins optional time section

Code.xsd
xsd:element name=“bedtime” type=“xsd.time:/>
Code.xml
<bedtime>20:15:05-05:00>/bedtime>
Date and Type Data Types

Built-in Datatypes (cont.)
Primitive Datatypes
 gDay
 gMonth
 hexBinary
 base64Binary
 anyURI
 QName
 NOTATION
Atomic, built-in
 format: ---DD
 format: --MM
 a hex string
 a base64 string
 http://www.aimit.ac.in
 a namespace qualified name
 a NOTATION from the XML spec

• Derived types
– normalizedString
– token
– language
– IDREFS
– ENTITIES
– NMTOKEN
– NMTOKENS
– Name
– NCName
– ID
– IDREF
– ENTITY
– integer
– nonPositiveInteger
• Subtype of primitive datatype
– A string without tabs, line feeds, or carriage returns
– String w/o tabs, l/f, leading/trailing spaces, consecutive spaces
– any valid xml:lang value, e.g., EN, FR, ...
– must be used only with attributes
– part (no namespace qualifier)
– mmust be used only with attributes
– ust be used only with attributes
– 456
– negative infinity to 0

• Derived types
– negativeInteger
– long
– int
– short
– byte
– nonNegativeInteger
– unsignedLong
– unsignedInt
– unsignedShort
– unsignedByte
– positiveInteger
• Subtype of primitive datatype
– negative infinity to -1
– -9223372036854775808 to 9223372036854775807
– -2147483648 to 2147483647
– -32768 to 32767
– -127 to 128
– 0 to infinity
– 0 to 18446744073709551615
– 0 to 4294967295
– 0 to 65535
– 0 to 255
– 1 to infinity
Note: the following types can only be used with attributes :
ID, IDREF, IDREFS, NMTOKEN, NMTOKENS, ENTITY, and ENTITIES.

Restrictions
Restrictions are used to define acceptable
values for XML elements or attributes. When
used with XML elements they are known as
“facets”.

Creating your own Datatypes
A new datatype can be defined from an
existing datatype (called the "base" type) by
specifying values for one or more of the
optional facets for the base type.

General Form of Creating a New
Datatype by Specifying Facet Values
<xsd:simpleType name= "name">
<xsd:restriction base= "xsd:source">
<xsd:facet value= "value"/>
<xsd:facet value= "value"/>
…
</xsd:restriction>
</xsd:simpleType>
Facets:
- length
- minlength
- maxlength
- pattern
- enumeration
- minInclusive
- maxInclusive
- minExclusive
- maxExclusive
...
Sources:
- string
- boolean
- number
- float
- double
- duration
- dateTime
- time
...

Restrictions
Constraint Description
enumeration Defines a list of acceptable values.
fractionDigits Specifies the maximum number of deicmal places allowed.
Must be equal to or greater than zero.
length Specifies the exact number of characters or list items allowed.
Must be absolute.
maxExclusive Specifies the upper bounds for numeric values.
maxInclusive Specifies the upper bounds for numeric values.
maxLength Specifies the maximum number of characters or list items
allowed. Must be absolute.
minExclusive Specifies the lower bounds for numeric values.
minInclusive Specifies the lower bounds for numeric values.
minLength Specifies the minimum number of characters or list items
allowed. Must be absolute.

Restrcitions
Constraint Description
pattern Defines the exact sequence of characters that are
acceptable.
totalDigits Specifies the exact number of digits allowed. Must be
greater than zero.
whiteSpace Specifies how white space is handled.

Example of Creating a New Datatype by
Specifying Facet Values
<xsd:simpleType name="TelephoneNumber">
<xsd:restriction base="xsd:string">
<xsd:length value=“15/>
<xsd:pattern value="d{4}-d{10}"/>
</xsd:restriction>
</xsd:simpleType>
1. This creates a new datatype called 'TelephoneNumber'.
2. Elements of this type can hold string values,
3. But the string length must be exactly 15 characters long and
4. The string must follow the pattern: dddd-dddddddddd, where 'd' represents
a 'digit'.
(Obviously, in this example the regular expression makes the length facet
redundant.)
1
2
3
4

Creating your own Datatypes
The string primitive datatype has six optional facets:
 length
 minLength
 maxLength
 pattern
 enumeration
 whitespace (legal values: preserve, replace, collapse)

Length
The facets length, minLength, maxLength allow to constrain the
length of an item like a string (also allow to constrain the number
of items in a list type).
Values of length, minLength, minLength should be non-negative
integers. Example:
<xsd:simpleType name="state">
<xsd:length value="2"/>
</xsd:restriction>
</xsd:simpleType>
defines a type state representing strings containing exactly two
characters.
 These facets supported by all primitive types other than numeric and date-
and time-related types. Also supported by list types.

White Space
This facet controls how white space in a value received from
the parser is processed, prior to Schema validation. It can
take three values:
 preserve: no white space processing, beyond what base XML does.
 replace: Convert every white space character (Line Feed, etc) to a
space character (#x20).
 collapse: Like replace. All leading or trailing spaces are then
removed. Also sequences of spaces are replaced by single spaces.
 Note analogies to “Normalization of Attribute Values” in base
XML.
All simple types except union types have this attribute, but
usually you don’t explicitly set it in restriction: just inherit
values from built in types.
All built in types have collapse, except string which has
preserve and normalizedString which has replace.

Pattern
Perhaps the most powerful facet is pattern, which
allows to specify a regular expression: any allowed
value must satisfy the pattern of this expression.
Example
<xsd:simpleType name="weekday">
<xsd:pattern
value="(Mon|Tues|Wednes|Thurs|Fri)day"/>
</xsd:restriction>
</xsd:simpleType>
 defines a type weekday representing the names of the
week days.

Regular Expressions
XML Schema has its own notation for regular
expressions, but very much based on the
corresponding Perl notation.
For the most part Schema use a subset of the
Perl 5 grammar for regular expressions.
 Includes most of the purely “declarative” features
from Perl regular expressions, but omits many
“procedural” features related to search, matching
algorithm, substitution, etc.

Metacharacters
The following characters, called metacharacters,
have special roles in Schema regular expressions:
 . ? * + | { } ( ) [ ]
To match these characters literally in patterns, must
escape them with , e.g.:
 The pattern “2+2” matches the string “2+2”.
 The pattern “f(x)” matches the string “f(x)”.

Escape Sequences
n
r
t

|
-
^
?
*
+
{
}
(
)
[
]
linefeed
carriage return
tab
The backward slash
The vertical bar |
The hyphen -
The caret ^
The question mark ?
The asterisk *
The plus sign +
The open curly brace {
The close curly brace }
The open paren (
The close paren )
The open square bracket [
The close square bracket ]

Escape Sequences
In general one should use XML character
references to include hard-to-type characters.
But for convenience Schema regular
expressions allow:
 n matches a newline character (same as 
)
 r matches a carriage return character (same as
)
 t matches a tab character (same as 	)

Escape Sequences
All other escape sequences (except - and ^,
used only in character class expressions)
match any single character out of some set of
possible values.
 For example d matches any decimal digit, so the
pattern “Boeing ddd” matches the strings
“Boeing 747”, “Boeing 777”, etc.

Multicharacter Escapes
The simplest patterns matching classes of
characters are:
 . matches any character except carriage return
or newline.
 d matches any decimal digit.
 s matches any white space character.
 i matches any character that can start an XML
name.
 c matches any character that can appear in an
XML name.
 w matches any “word” character (excludes
punctuation, etc.)

Multicharacter Escapes
The escapes D, S, I, C and W are
negative forms, e.g. D matches any character
except a decimal digit.

Category Escapes
A large and interesting family of escapes is based on
the Unicode standard. General form is
p{Name}
where Name is a Unicode-defined class name.
 The negative form P{Name} matches any character not
in the class.
Simple examples include: p{L} (any letter), p{Lu}
(upper case letters), p{Ll} (lower case letters), etc.
More interesting cases are based on the Unicode
block names for alphabets, e.g.:
 p{IsBasicLatin}, p{IsLatin-1Supplement}, p{IsGreek},
p{IsArabic}, p{IsDevanagari}, p{IsHangulJamo},
p{IsCJKUnifiedIdeographs}, etc, etc, etc.

Category Escapes
p{L}
p{Lu}
p{Ll}
p{N}
p{Nd}
p{P}
p{Sc}
A letter, from any language
An uppercase letter, from any language
A lowercase letter, from any language
A number - Roman, fractions, etc
A digit from any language
A punctuation symbol
A currency sign, from any language

Character Class Expressions
Allow you to define terms that match any
character from a custom set of characters.
Basic syntax is familiar from Perl and UNIX:
[List-of-characters]
or the negative form:
[^List-of-characters]
Here List-of-characters can include individual
characters, and also ranges of the form First-
Last where First and Last are characters.

Character Class Expressions
Examples:
 [RGB] matches one of R, G, or B.
 [0-9A-F] or [dA-F] match one of 0, 1, …, 9, A, B,…, F.
 [^rn] matches anything except CR, NL (same as . ).

Restriction Example - Series
<xs:element name=“char">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:pattern value=“[a-z]"/>
</xs:restriction>
</xs:simpleType>
</xs:element>

<xs:element name=“choice">
<xs:simpleType>
<xs:pattern value=“nyNY"/>
</xs:restriction>
</xs:simpleType>
</xs:element>

Class Subtractions
A feature of XML Schema, not present in Perl 5.
A class character expression can take the form:
[List-of-characters-Class-char-expr]
or:
[^List-of-characters-Class-char-expr]
where Class-char-expr is another class
character expression.
Example:
 [a-zA-Z-[aeiouAEIOU]] matches any consonant in
the Latin alphabet.

Sequences and Alternatives
Finally, the universal core of regular
expressions. If Pattern1 and Pattern2 are
regular expressions, then:
 Pattern1Pattern2 matches any string made by
putting a string accepted by Pattern1 in front of a
string accepted by Pattern2.
 Pattern1|Pattern2 matches any string that would
be accepted by Pattern1, or any string accepted
by Pattern2.
Parentheses just group things together:
 (Pattern1) matches any string accepted by
Pattern1.

<xs:element name="initials">
<xs:simpleType>
<xs:pattern value="[a-zA-Z][a-zA-Z][a-zA-Z]"/>
</xs:restriction>
</xs:simpleType>
</xs:element>

<xs:element name=“areacode">
<xs:simpleType>
<xs:restriction base="xs:integer">
<xs:pattern value=“[0-9][0-9][0-9]"/>
</xs:restriction>
</xs:simpleType>
</xs:element>

Quantifiers
If Pattern1 is a regular expression:
 Pattern1? matches the empty string or any string
accepted by Pattern1.
 Pattern1+ matches any string accepted by Pattern1,
or by Pattern1Pattern1, or by
Pattern1Pattern1Pattern1, or …
 Pattern1* matches the empty string or any string
accepted by Pattern1+.

Regular Expressions
Regular Expression
Chapter d
Chapter d
Chaptersd
a*b
[xyz]b
a?b
a+b
[a-c]x
[-ac]x
[ac-]x
[^0-9]x
Dx
Example
Chapter 1
Chapter 1
Chapter followed by a blank followed by a digit
b, ab, aab, aaab, …
xb, yb, zb
b, ab
ab, aab, aaab, …
ax, bx, cx
-x, ax, cx
ax, cx, -x
any non-digit char followed by x
any non-digit char followed by x

Quantifiers
If n, m are numbers, XML Schema also allow the
shorthand forms:
 Pattern1{n} is equivalent to Pattern1 repeated n
times.
 Pattern1{m,n} matches any string accepted by
Pattern1 repeated m times or m + 1 times or … or n
times.
 Pattern1{m,} matches any string accepted by
Pattern1 repeated m or more times.

Regular Expressions (cont.)
Regular Expression
 (ho){2} there
 (hos){2} there
 .abc
 (a|b)+x
 a{1,3}x
 a{2,}x
 wsw
Example
 hoho there
 ho ho there
 any (one) char followed by abc
 ax, bx, aax, bbx, abx, bax,...
 ax, aax, aaax
 aax, aaax, aaaax, …
 word character
(alphanumeric plus dash)
followed by a space followed by
a word character

Regular Expressions (cont.)
[a-zA-Z-[Ol]]* • A string comprised of any
lower and upper case
letters, except "O" and "l"
. • The period "." (Without the
backward slash the period
means "any character")

Example of Derived Simple Type
(Regular expression)
<xsd:simpleType name=“ProductKey">
<xsd:pattern value="d{3}-[A-Z]{2}"/>
</xsd:restriction>
</xsd:simpleType>

Restrictions – Password Example
<xs:element name="password">
<xs:simpleType>
<xs:pattern value="[a-zA-Z0-9]{8}"/>
</xs:restriction>
</xs:simpleType>
</xs:element>
This element must contain a literal string composed of
upper or lower case letters, or numerals. It must
have 8 characters in total.

Using Patterns in Restriction
All simple types (including lists and enumerations)
support the pattern facet, e.g.:
<simpleType name=“multiplesOfFive">
<restriction base="xs:integer">
<pattern value=“[+-]?d*[05]"/>
</restriction>
</simpleType>
defines a subtype of integer including all numbers
ending with digits 0 or 5.

Example R.E.
[1-9]?[0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5]
0 to 99 100 to 199 200 to 249 250 to 255
This regular expression restricts a string to have
values between 0 and 255.
… Such a R.E. might be useful in describing an
IP address ...

IP Datatype Definition
<xsd:simpleType name="IP">
<xsd:pattern value="(([1-9]?[0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5]).){3}
([1-9]?[0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])">
<xsd:annotation>
<xsd:documentation>
Datatype for representing IP addresses. Examples,
129.83.64.255, 64.128.2.71, etc.
This datatype restricts each field of the IP address
to have a value between zero and 255, i.e.,
[0-255].[0-255].[0-255].[0-255]
Note: in the value attribute (above) the regular
expression has been split over two lines. This is
for readability purposes only. In practice the R.E.
would all be on one line.
</xsd:documentation>
</xsd:annotation>
</xsd:pattern>
</xsd:restriction>
</xsd:simpleType>

Regular Expressions (concluded)
p{L}
p{Lu}
p{Ll}
p{N}
p{Nd}
p{P}
p{Sc}
A letter, from any language
An uppercase letter, from any language
A lowercase letter, from any language
A number - Roman, fractions, etc
A digit from any language
A punctuation symbol
A currency sign, from any language
<xsd:simpleType name="money">
<xsd:pattern value="p{Sc}p{Nd}+(.p{Nd}p{Nd})?"/>
</xsd:restriction>
</xsd:simpleType>
<xsd:element name="cost" type="money"/>
"currency sign from any language, followed
by one or more digits from any language,
optionally followed by a period and
two digits from any language"
<cost>$45.99</cost>
<cost>¥300</cost>

Enumeration
The enumeration facet allows one to select a finite
subset of allowed values from a base type, e.g.:
<xsd:simpleType name="weekday">
<xsd:restriction base="xs:string">
<xsd:enumeration value="Monday"/>
<xsd:enumeration value="Tuesday"/>
<xsd:enumeration value="Wednesday"/>
<xsd:enumeration value="Thursday"/>
<xsd:enumeration value="Friday"/>
</xsd:restriction>
</xsd:simpleType>
 Behaves like a very restricted version of pattern?
 All primitive types except boolean support the enumeration
facet. List and union types also support this facet.

Example of Derived Simple Type 3
(Enumeration)
<xsd:simpleType name="State">
<xsd:enumeration value="AP"/>
<xsd:enumeration value=“KA"/>
<xsd:enumeration value="TN/>

</xsd:restriction>
</xsd:simpleType>
enumeration facet limits a simple type to a set of distinct
values

Restriction Example - Set
<xs:element name=“car">
<xs:simpleType>
<xs:enumeration value=“Maruthi“ />
<xs:enumeration value=“Fiat“/>
<xs:enumeration value=“Ford“ />
<xs:enumeration value=“Tata“ />
<xs:enumeration value=“Santro” />
</xs:restriction>
</xs:simpleType>
</xs:element>

Enumeration
An enumeration restricts the value to be one of a
fixed set of values
Example:
 <xs:element name="season">
<xs:simpleType>
<xs:enumeration value="Spring"/>
<xs:enumeration value="Summer"/>
<xs:enumeration value="Autumn"/>
<xs:enumeration value="Fall"/>
<xs:enumeration value="Winter"/>
</xs:restriction>
</xs:simpleType>
</xs:element>

Another Example
<xsd:simpleType name="shape">
<xsd:enumeration value="circle"/>
<xsd:enumeration value="triangle"/>
<xsd:enumeration value="square"/>
</xsd:restriction>
</xsd:simpleType>
This creates a new type called shape.
An element declared to be of this type
must have either the value circle, or triangle, or square.

Enumeration - Example
<xsd:simpleType name=“GenderType”>
<xsd:restriction base=“token”>
<xsd:enumeration value=“M”/>
<xsd:enumeration value=“F”/>
<xsd:enumeration value=“NK”/>
</xsd:restriction>
</xsd:simpleType>
<xsd:element name=“Gender” type=“GenderType”/>
<Gender>NK</Gender>
<Gender>Male</Gender>

Using Patterns in Restriction
The pattern facet can appear more than once
in a single restriction: interpretation is as if
patterns were combined with |.
 Conversely if the pattern facet is specified in
restriction of a base type that was itself defined
using a pattern, allowed values must satisfy both
patterns.

Multiple Facets - "and" them together, or
"or" them together?
An element declared to
be of type
TelephoneNumber must
be a string of length=8
and the string must
follow the pattern: 3
digits, dash, 4 digits.
<xsd:simpleType name="shape">
<xsd:enumeration value="circle"/>
<xsd:enumeration value="triangle"/>
<xsd:enumeration value="square"/>
</xsd:restriction>
</xsd:simpleType>
<xsd:simpleType name="TelephoneNumber">
<xsd:pattern value="d{3}-d{4}"/>
</xsd:restriction>
</xsd:simpleType>
An element declared to be
of type shape must be a
string with a value of either
circle, or triangle, or
square.
Patterns, enumerations => "or" them together
All other facets => "and" them together

Numerical - Facets
The facets maxInclusive, maxExclusive,
minExclusive, minInclusive are supported
only by numeric and date- and time-related
types, and define bounds of value ranges.
The facets totalDigits, fractionDigits are
defined for the primitive type decimal, and
thus all numeric types derived from decimal,
and for no other types.

Facets of the integer Datatype
The integer datatype has 8 optional facets:
 totalDigits
 pattern
 whitespace
 enumeration
 maxInclusive
 maxExclusive
 minInclusive
 minExclusive

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 < the given value
totalDigits -- number must have exactly value digits
fractionDigits -- number must have no more than value digits
after the decimal point

A Simple Type Example (1 of 4)
Integer with value (1234, 5678]
<xsd:simpleType name=‘MyInteger’>
<xsd:restriction base=‘xsd:integer’>
<xsd:minExclusive value=‘1234’/>
<xsd:maxInclusive value=‘5678’/>
</xsd:restriction>
</xsd:simpleType>

Integer with value [1234, 5678)
<xsd:minInclusive value=‘1234’/>
<xsd:maxExclusive value=‘5678’/>
</xsd:restriction>
</xsd:simpleType>

Integer with value [1234, 5678]
<xsd:minInclusive value=‘1234’/>
</xsd:restriction>
</xsd:simpleType>

Validating integer with value (1234, 5678]
<data xsi:type='MyInteger'></data> INVALID
<data xsi:type='MyInteger'>Sandy</data> INVALID
<data xsi:type='MyInteger'>-32</data> INVALID
<data xsi:type='MyInteger'>1233</data> INVALID
<data xsi:type='MyInteger'>1235</data>
<data xsi:type='MyInteger'>5678</data>
<xsd:minExclusive value=‘1234’/>
</xsd:restriction>
</xsd:simpleType>

Restriction Example - Simple
<xs:element name="age">
<xs:simpleType>
<xs:minInclusive value="0"/>
<xs:maxInclusive value="120"/>
</xs:restriction>
</xs:simpleType>
</xs:element>

Simple Type Definition
Example
<xs:simpleType name="farenheitWaterTemp">
<xs:restriction base="xs:number">
<xs:fractionDigits value="2"/>
<xs:minExclusive value="0.00"/>
<xs:maxExclusive value="100.00"/>
</xs:restriction>
</xs:simpleType>

Fixing a Facet Value
Sometimes when we define a simpleType we
may like to have a unchanging value for one (or
more) facet. That is, we want to make the facet
a constant.
<xsd:simpleType name= "ClassSize">
<xsd:restriction base="xsd:nonNegativeInteger">
<xsd:minInclusive value="10" fixed="true"/>
</xsd:restriction>
</xsd:simpleType>
simpleTypes which derive from this simpleType may not change this facet.

<xsd:simpleType name= "ClassSize">
<xsd:restriction base="xsd:nonNegativeInteger">
<xsd:minInclusive value="10" fixed="true"/>
</xsd:restriction>
</xsd:simpleType>
<xsd:simpleType name= “MCAClassSize">
<xsd:restriction base="ClassSize">
<xsd:minInclusive value="15"/>
</xsd:restriction>
</xsd:simpleType>
Error! Cannot
change the value
of a fixed facet!

PurchaseOrder.xsd
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<xsd:annotation>
<xsd:documentation xml:lang="en">
Sample Purchase order schema
</xsd:documentation>
</xsd:annotation>
<xsd:element name="purchaseOrder" type="PurchaseOrderType"/>
<xsd:element name="comment" type="xsd:string"/>
<xsd:sequence>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="Address">
<xsd:sequence>
<xsd:element name="name" type="xsd:string"/>
<xsd:element name="street" type="xsd:string"/>
<xsd:element name="city" type="xsd:string"/>
<xsd:element name="state" type="xsd:string"/>
<xsd:element name="zip" type="xsd:decimal"/>
</xsd:sequence>
<xsd:attribute name="country" type="xsd:NMTOKEN"
fixed="IN"/>
</xsd:complexType>
<xsd:complexType name="Items">
<xsd:sequence>
<xsd:element name="item" minOccurs="0"
maxOccurs="unbounded">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="productName" type="xsd:string"/>
<xsd:element name="quantity">
<xsd:simpleType>
<xsd:restriction base="xsd:positiveInteger">
<xsd:maxExclusive value="100"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:element>
<xsd:element name="Price" type="xsd:decimal"/>
<xsd:element name="shipDate" type="xsd:date"
minOccurs="0"/>
</xsd:sequence>
<xsd:attribute name="partNum" type="SKU"
use="required"/>
</xsd:complexType>
</xsd:element>
</xsd:sequence>
</xsd:complexType>

<xsd:simpleType name="SKU">
<xsd:pattern value="d{3}-[A-Z]{2}"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:schema>

List Type
We define a type representing a white-space-
separated list of items using the list element.
 Comprised of sequences of atomic simple types
A list value is split according to its white space
content prior to validation of the items in the
list
 Three built-in list types
 NMTOKENS, IDREFS, ENTITIES
 User defined List type
 Derive from atomic types
 Facets
 length, minLength, maxLength, enumeration.

Example of List Type
The xsd:list element creates a new simple type that
allows the element to contain a sequence of values
of the base type, which are separated with white
space characters (spaces, tabs, or line breaks).
Schema
<xsd:simpleType name="listOfMyIntType">
<xsd:list itemType="myInteger"/>
</xsd:simpleType>
Instance Document
<listOfMyInt>20003 15037 95977 95945</listOfMyInt>

Example: List Type with Facet
list of integers where 5 is the maximum
number of items allowed in the list.
<xs:simpleType name='derivedlistOfIntegers'>
<xs:restriction base='listOfIntegers'>
<xs:maxLength value='5'>
</xs:restriction>
</xs:simpleType>
 Usage in XML instance document
<myelement listOfIntegers='1 100 9 4000 0'/>

List Type for Five Colors
<xsd:simpleType name="ColorList">
<xsd:list itemType="Color"/>
</xsd:simpleType>
<xsd:simpleType name="FiveColors">
<xsd:restriction base="ColorList">
</xsd:restriction>
</xsd:simpleType>
Use in XML instance document
<fiveColors>white black blue red green</fiveColors>

<xsd:simpleType name=“StateList">
<xsd:list itemType=“State"/>
</xsd:simpleType>
<xsd:simpleType name="SixStates">
<xsd:restriction base=“StateList">
</xsd:restriction>
</xsd:simpleType>
<element name=“SelectedStates” type=“SixStates”>
Define a list of exactly six states (SelectedStates), we first
define a new list type called StateList from State, and then we
derive SixStates by restricting StateList to only six items
< SelectedStates>KA KL GA TN AP MP</SelectedStates>

Notes about the list type
You cannot create a list of lists
 i.e., you cannot create a list type from another list type.
You cannot create a list of complexTypes
 i.e., lists only apply to simpleTypes
In the instance document, you must separate each item in a
list with white space (blank space, tab, or carriage return)
The only facets that you may use with a list type are:
 length: use this to specify the length of the list
 minLength: use this to specify the minimum length of the list
 maxLength: use this to specify the maximum length of the list
 enumeration: use this to specify the values that the list may have
 pattern: use this to specify the values that the list may have

Union Type
The xsd:union element creates a new simple
type that allows the element to contain a
value that conforms to any one of a group of
specified base types.

Creating a simpleType that is a Union of Types
simpleType 1 simpleType 2
simpleType 1
+
simpleType 2
Note: you can create a union of more
than just two simpleTypes

Methods for creating Union simpleType
<xsd:simpleType name="name">
<xsd:union memberTypes="space delimited simpleTypes"/>
</xsd:simpleType>
Alternatively,
<xsd:simpleType name="name">
<xsd:union>
<xsd:simpleType>
…
</xsd:simpleType>
<xsd:simpleType>
…
</xsd:simpleType>
…
</xsd:union>
</xsd:simpleType>

Union Type for Zipcodes
<xsd:simpleType name="zipUnion">
<xsd:union memberTypes=“State listOfMyIntType"/>
</xsd:simpleType>
<element name=zips type=“zipUnion”>
<zips>KA</zips>
<zips>575001 613256 715872</zips>
<zips>UP</zips>

<xs:simpleType name="toddlerCounting">
<xs:union>
<xs:simpleType>
<xs:minInclusive value="1"/>
</xs:restriction>
</xs:simpleType>
<xs:simpleType>
<xs:enumeration value="many"/>
</xs:restriction>
</xs:simpleType>
</xs:union>
</xs:simpleType>
Simple Types : Union

union of two simple types.
<xs:attribute name="fontsize">
<xs:simpleType>
<xs:union memberTypes="fontbynumber fontbystringname" />
</xs:simpleType>
</xs:attribute>
<xs:simpleType name="fontbynumber">
<xs:restriction base="xs:positiveInteger">
</xs:restriction>
</xs:simpleType>
<xs:simpleType name="fontbystringname">
<xs:enumeration value="small"/>
<xs:enumeration value="medium"/>
<xs:enumeration value="large"/>
</xs:restriction>
</xs:simpleType>

union of two simple types.
<xs:attribute name="MonitorSize">
<xs:simpleType>
<xs:union memberTypes="sizebynumber sizebystringname" />
</xs:simpleType>
</xs:attribute>
<xs:simpleType name="sizebynumber">
<xs:restriction base="xs:positiveInteger">
</xs:restriction>
</xs:simpleType>
<xs:simpleType name="sizebystringname">
<xs:enumeration value="small"/>
<xs:enumeration value="medium"/>
<xs:enumeration value="large"/>
</xs:restriction>
</xs:simpleType>

Prohibiting Derivation
You may, for some reason, have a simple type that you
don’t want anybody to derive further types from.
Do this by specifying the final attribute on the
<simpleType> element. Its value is a list containing a
subset of values from list, union, restriction,
extension.
Give the final attribute the value “#all” for blanket
prohibition of any derivation from this simple type.
 Can also prevent the value of individual facets from being
changed in subsequent restrictions by specifying
fixed="true" on the facet elements.

Prohibit XML Schema Derivations
The final attribute
 Can be used in
 xs:complexType
 xs:simpleType
 xs:element
 Can take values of
 restriction
 extension
 #all (any derivation)
The fixed attribute
 Can only be used in
xs:simpleType
 When it is set to true, it
cannot be further
modified
<xs:complexType name="characterType" final="#all">
<xs:sequence>
<xs:element name="name" type="nameType"/>
<xs:element name=“age" type=“ageType"/>
<xs:element name="qualification" type="descType"/>
</xs:sequence>
</xs:complexType>
<xs:simpleType name=“fixedString">
<xs:maxLength value="32" fixed="true"/>
</xs:restriction>
</xs:simpleType>

Complex Types
Complex Types define logical structures with
attributes and nested elements
They use a sequence, choice or all
containing elements that use Simple Types or
other Complex Types
May reference types defined elsewhere in the
schema or imported using import statement

Definition – complex type
<xsd:sequence>
</xsd:sequence>
</xsd:complexType>
Define the complex type “purchaseOrderType”
 Allow elements & attributes
 contain a set of element declarations, element references, and attribute
declarations.
element declarations
attribute declaration
element reference

Element Content
Three different ways
 Complex types from simple types
 Mixed content
 Elements mixed with character content
 Empty content

XML-Schema : Mixed, Empty and Any Content
Mixed content is used if you want to model elements
that includes both subelements and character data
Empty content is used to define elements that do not
include any subelements and character data
Any content (the most basic data type) does not
constrain the content in any way

Example : Defining a complexType
<complexType name= “Customer”>
<sequence>
<element name= “Person” type=“Name” />
<element name= “Address” type=“AddressT” />
</sequence>
</complexType>
<complexType name=“AddressT”>
<sequence>
<element name=“Street” type=“string” />
<element name=“City” type=“string” />
<element name=“State” type=“State_Region” />
<element name=“PostalCode” type=“string” />
<element name=“Country” type=“string” />
</sequence>

</complexType>

Complex Type from a Simple Type
<xsd:element name="internationalPrice">
<xsd:complexType>
<xsd:simpleContent>
<xsd:extension base="xsd:decimal">
<xsd:attribute name="currency” type="xsd:string" />
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
</xsd:element>
XML Instance:
<internationalPrice currency="EUR">423.46</internationalPrice>

Mixed elements
Mixed elements may contain both text and
elements
We add mixed="true" to the xs:complexType element
<xs:complexType name="paragraph" mixed="true">
<xs:sequence>
<xs:element name="someName" type="xs:anyType"/>
</xs:sequence>
</xs:complexType>

Mixed Content
Sub-elements mixed with character data
<letterBody>
<salutation>Dear Mr.<name>Anu Malik</name>.
</salutation>Your order of <quantity>1</quantity>
<productName>LCD Monitor</productName>
shipped from our warehouse on <shipDate>2009-09-
18</shipDate>. ....
</letterBody>

Mixed Content
<xsd:element name="letterBody">
<xsd:complexType mixed="true">
<xsd:sequence>
<xsd:element name="salutation">
<xsd:complexType mixed="true"> 
</xsd:sequence>
</xsd:complexType>
</xsd:element>

Empty Elements
XML Schema doesn’t have any unique way of
representing elements that must be empty.
The simplest thing to do this is simply omit the
allowed element content in a complex content
restriction.
Can such an element also be mixed (i.e. have
pure text content)?
 Logically it seems this should be possible
 But it seems to be forbidden by the XML Schema
specification, which singles out this case and says
such an element is strictly empty.

Empty Elements
To specify Empty type of element, define the
element’s type using the xsd:complexType
element, but omit the content model.
<xsd:element name=”BR”>
<xsd:complexType>
</xsd:complexType>
</xsd:element>
The following is a conforming element:
 
as is this one:


Empty Content
<img src="xml.gif" alt="Programming XML image"/>
<xsd:element name="img">
<xsd:complexType>
<xsd:attribute name="src“ type="xsd:NMTOKEN"/>
<xsd:attribute name="alt" type="xsd:string"/>
</xsd:complexType>
</xsd:element>

Complex Type Hierarchy
There are no built in complex types, other than
the so-called ur-type, represented as
xsd:anyType.
All other complex types are derived by one or
more steps of restriction and extension from
xsd:anyType.
 Complex types can also be created by extension
of a simple type, but simple types are also
notionally restrictions of xsd:anyType.

Restriction
A restriction of a base type is a new type.
All allowed instances of the new type are also
instances of the base type. But the restricted type
doesn’t allow all possibilities allowed by the base
type.
 Think of the example of restricting xsd:string to 4
characters using the length facet. Strings of length 4 are
also allowed by the xsd:string, but the new type is more
restrictive.
 In the complex case, we might have a complex base type
that allows attribute att optionally. A restricted type might
not allow att at all.
 Another restriction of the same base might require att.
 Or we might have a base type that allows 0 or more nested
elm elements. The restricted type might require exactly 1
nested elm element.

Extension
An extension of a base type is a new type.
An extension allows extra attributes or extra content
that are not allowed in instances of the base type.
 At first brush this sounds like the opposite of restriction,
but this isn’t strictly true.
 If, for example, type E extends a type B by adding a
required attribute att, then instances of B are not allowed
instances of E (because they don’t have the required
attribute). So we have that E is an extension of B, but
there is no sense in which B could be a restriction of E.
 Some such inverse relation exists if all extra
attributes and content are optional in the extended
type, but this isn’t a required feature of extension.

Remarks
When one restricts a type one generally must
specify all allowed element content and
attributes.
When one extends a type one generally must
specify just the extra element content and
attributes.

Complex Content and Simple Content
We have seen that XML Schema complex types define
both some allowed nested elements, and some
allowed attribute specifications. Complex types that
allow nested elements are said to have complex
content.
But Schema distinguish as a special case complex
types having simple content—elements with such
types may have attributes, but they cannot have
nested elements.
This is presumably a useful distinction, but it does
introduce one more layer of complexity into the syntax
for complex type derivation.

Complex Content and Simple Content
Simple
Type
Complex
Type
Simple
Content
Complex
Content
Type
allows attributes or elements?
allows elements in
content?

Simple contents
A good example of complex elements with simple
content is the <textarea> element in HTML
documents. It accepts a text string as the content
with no sub (child) element and some attributes.
<xs:element name="textarea">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute name="name" type="xs:string"/>
<xs:attribute name="cols" type="xs:positiveInteger"/>
<xs:attribute name="rows" type="xs:positiveInteger"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>

Simple contents
Simple contents contain only attributes
 E.g.
<xs:element name="organism">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute name="taxonomy_id" type="xs:integer"
use="required"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>

Simple content type
<xsd:complexType>
<xsd:simpleContent>
<xsd:extension base="xsd:decimal">
<xsd:attribute name="currency” type="xsd:string" />
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
</xsd:element>
<internationalPrice currency="EUR">423.46</internationalPrice>
simpleContent indicates that the content model of the new type
contains only character data and no element declaration

Complex contents
Elements including children are defined as
complex types with complex content
 E.g.
<xs:element name="protein_set">
<xs:complexType>
<xs:complexContent>
<xs:restriction base="xs:anyType">
<xs:sequence>
<xs:element ref="protein" maxOccurs="unbounded"/>
</xs:sequence>
</xs:restriction>
</xs:complexContent>
</xs:complexType>
</xs:element>

Basic Forms of Complex Type Definition
Restriction Extension
<complexType>
<complexContent>
<restriction base="type">
allowed element content
allowed attributes
</restriction>
</complexContent>
</complexType>
<complexType>
<complexContent>
<extension base="type">
extra element content
extra attributes
</extension>
</complexContent>
</complexType>
<complexType>
<simpleContent>
<restriction base="type">
facet restrictions
allowed attributes
</restriction>
</simpleContent>
</complexType>
<complexType>
<simpleContent>
<extension base="type">
extra attributes
</extension>
</simpleContent>
</complexType>

Requirements on Base Type
The base type must be a complex type in all
cases except simpleContent/extension
(lower right in table shown in the previous
slide), in which case the base can be a
simple type.

Schematic Inheritance Diagram
xsd:anyType
Simple Types
Simple
Content
Complex
Content
extension
restriction
restriction
restriction
Complex
Types
restriction
list
union
restriction
extension
restriction
extension
restriction

Defining a Complex Type with no Base?
Actually the XML Schema specification says that:
<complexType>
<complexContent>
<restriction base="xsd:anyType">
allowed element content
allowed attributes
</restriction>
</complexContent>
</complexType>
<complexType>
allowed element
content
allowed attributes
</complexType>
 So in reality we were
directly restricting the
ur-type, which allows
any attributes and any
content!
Is “shorthand” for

Empty Content - 1
<internationalPrice currency=“EUR” value=“345.23”/>
<xsd:complexType>
<xsd:complexContent>
<xsd:restriction base="xsd:anyType">
<xsd:attribute name="currency" type="xsd:string"/>
<xsd:attribute name="value” type="xsd:decimal"/>
</xsd:restriction>
</xsd:complexContent>
</xsd:complexType>
</xsd:element>

Empty Content - 2
<xsd:complexType>
<xsd:attribute name="currency” type="xsd:string"/>
<xsd:attribute name="value” type="xsd:decimal"/>
</xsd:complexType>
</xsd:element>
A complex type defined without complexContent is
interpreted as shorthand for complex content that
restricts anyType

XSD Complex Types Indicators
We have seven types of indicators:
 Order indicators:
 All
 Choice
 Sequence
 Occurrence indicators:
 maxOccurs
 minOccurs
 Group indicators:
 Group name
 attributeGroup name

Defining Element Content
Where we wrote allowed element content or
extra element content in the syntax for
complex type definitions, what should appear
is a model group.
A model group is exactly one of:
 an <xsd:sequence/> element, or
 an <xsd:choice/> element, or
 an <xsd:all/> element.
(The element content appearing in the type definition may
also be a globally defined model group, referenced through an
<xsd:group/> element. The global definition—a named
<xsd:group/> element—just contains one of the three
elements above.)

Sequence
A <xsd:sequence/> model group contains a series of
particles. A particle is an <xsd:element/> element,
another model group, or a wildcard.
As expected, this model just says the element content
represented by those items should appear in
sequence.
E.g.
<xsd:sequence>
<xsd:element ref="title"/>
<xsd:element ref="paragraph"
minOccurs="0“ maxOccurs="unbounded"/>
</xsd:sequence>

xs:sequence
We’ve already seen an example of a complex
type whose elements must occur in a specific
order:
<xs:element name="person">
<xs:complexType>
<xs:sequence>
<xs:element name="firstName" type="xs:string" />
<xs:element name="lastName" type="xs:string" />
</xs:sequence>
</xs:complexType>
</xs:element>

Complex Types
(title?,firstname*,lastname)
<xsd:complexType name="name">
<xsd:sequence>
<xsd:element name="title" minOccurs="0"/>
<xsd:element name="firstname" minOccurs="0"
maxOccurs="unbounded"/>
<xsd:element name="lastname"/>
</xsd:sequence>
</xsd:complexType>

XML Schema Definition (XSD) Explained

XML Schema Definition (XSD) Explained

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