Group items tagged

the import element has optional namespace and schemaLocation attributes. If present, the schemaLocation attribute is understood in a way which parallels the interpretation of xsi:schemaLocation

The default value for both the minOccurs and the maxOccurs attributes is 1.

Be sure that if you specify a value for only the minOccurs attribute, it is less than or equal to the default value of maxOccurs,

Attributes may appear once or not at all, but no other number of times

The existence of a substitution group does not require any of the elements in that class to be used

Several facets can be applied to list types: length, minLength, maxLength, pattern, and enumeration

<xsd:simpleType name="USStateList"> <xsd:list itemType="USState"/> </xsd:simpleType> <xsd:simpleType name="SixUSStates"> <xsd:restriction base="USStateList"> <xsd:length value="6"/> </xsd:restriction> </xsd:simpleType>

Note that it is possible to derive a list type from the atomic type string. However, a string may contain white space, and white space delimits the items in a list type, so you should be careful using list types whose base type is string.

The include mechanism enables you to use externally created schema components "as-is", that is, without any modification.

<complexType name="Address">

base="ipo:Address"

</redefine>

The redefine element acts very much like the include element as it includes all the declarations and definitions from the address.xsd file

Outside of the redefine element, any such attempt to define a complex type with the same name (and in the same namespace) as the base from which it is being derived would cause an error.

Now that Address has been redefined, the extension applies to all schema components that make use of Address

Substitution GroupsXML Schema provides a mechanism, called substitution groups, that allows elements to be substituted for other elements. More specifically, elements can be assigned to a special group of elements that are said to be substitutable for a particular named element called the head element. (Note that the head element as well as the substitutable elementsmust be declared as global elements

Elements in a substitution group must have the same type as the head element, or they can have a type that has been derived from the head element's type

<element name="shipComment" type="string" substitutionGroup="ipo:comment"/>

substitutionGroup="ipo:comment"/>

<ipo:shipComment>

<ipo:customerComment>

global declarations cannot contain the attributes > minOccurs > , > maxOccurs > , or > use > . >

Abstract Elements and TypesXML Schema provides a mechanism to force substitution for a particular element or type. When an element or type is declared to be "abstract", it cannot be used in an instance document. When an element is declared to be abstract, a member of that element's substitution group must appear in the instance document. When an element's corresponding type definition is declared as abstract, all instances of that element must use xsi:type to indicate a derived type that is not abstract.

Declaring an element as abstract requires the use of a substitution group. Declaring a type as abstract simply requires the use of a type derived from it (and identified by the xsi:type attribute) in the instance document

the redefine mechanism we describe here enables you to redefine simple and complex types, groups, and attribute groups that are obtained from external schema files. Like the include mechanism, redefine requires the external components to be in the same target namespace as the redefining schema,

abstract="true"

abstract="true"

extension base

extension

extension

xsi:type="Car"

Controlling the Creation & Use of Derived Types

schema authors will sometimes want to control derivations of particular types, and the use of derived types in instances.

to specify that for a particular complex type, new types may not be derived from it, either (a) by restriction, (b) by extension, or (c) at all.

substitutionGroup=

The restriction value of the final attribute prevents derivations by restriction. Preventing derivations at all, or by extension, are indicated by the values #all and extension respectively

an optional finalDefault attribute on the schema element whose value can be one of the values allowed for the final attribute. The effect of specifying the finalDefault attribute is equivalent to specifying a final attribute on every type definition and element declaration in the schema.

When a simple type is defined, the fixed attribute may be applied to any of its facets to prevent a derivation of that type from modifying the value of the fixed facets.

fixed="true"

a mechanism that controls which derivations and substitution groups may be used in instance documents

eplacement by derived types can be controlled using the block attribute in a type definition

final="restriction"

final="restriction"

Preventing replacement by derivations at all, or by derivations-by-extension, are indicated by the values #all and extension respectively. As with final, there exists an optional blockDefault attribute on the schema element whose value can be one of the values allowed for the block attribute.

block="restriction"

final="restriction"

mechanism that enables schema components from different target namespaces to be used together, and hence enables the schema validation of instance content defined across multiple namespaces.

Importing Types

only global schema components can be imported:

Only named complex types can be imported; local, anonymously defined types cannot.

each namespace must be identified with a separate import element.

The import elements themselves must appear as the first children of the schema element

each namespace must be associated with a prefix, using a standard namespace declaration

import elements optionally contain a schemaLocation attribute to help locate resources associated with the namespaces.

ref="xipo:

Deriving Types by Extension

we indicate that the content models of the new types are complex, i.e. contain elements, by using the complexContent element, and we indicate that we are extending the base type Address by the value of the base attribute on the extension element.

xsi:type="ipo:UKAddress">

xsi:type="ipo:USAddress">

Deriving Complex Types by Restriction

the values represented by the new type are a subset of the values represented by the base type (as is the case with restriction of simple types).

<complexContent> <restriction base=

Table 3 shows several examples of how element and attribute declarations within type definitions may be restricted

XML Schema became a W3C Recommendation 02. May 2001.

You don't have to learn a new language You can use your XML editor to edit your Schema files You can use your XML parser to parse your Schema files You can manipulate your Schema with the XML DOM You can transform your Schema with XSLT

XML Schemas are Extensible

Reuse your Schema in other Schemas Create your own data types derived from the standard types Reference multiple schemas in the same document

Well-Formed is not Enough

targetNamespace="http://www.w3schools.com" indicates that the elements defined by this schema (note, to, from, heading, body.) come from the "http://www.w3schools.com" namespace.

xmlns:xs="http://www.w3.org/2001/XMLSchema" indicates that the elements and data types used in the schema come from the "http://www.w3.org/2001/XMLSchema" namespace.

prefixed with xs:

xmlns="http://www.w3schools.com" indicates that the default namespace is "http://www.w3schools.com".

Referencing a Schema in an XML Document

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.w3schools.com note.xsd"

This 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

The syntax for defining a simple element is: <xs:element name="xxx" type="yyy"/>

built-in data types

xs:string xs:decimal xs:integer xs:boolean xs:date xs:time

A default value is automatically assigned to the element when no other value is specified.

default="red"/

A fixed value is also automatically assigned to the element, and you cannot specify another value.

fixed="red"/

<xs:complexType name="fullpersoninfo"> <xs:complexContent> <xs:extension base="personinfo">

Restrictions 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.

<xs:restriction base="xs:string"> <xs:enumeration value="Audi"/> <xs:enumeration value="Golf"/> <xs:enumeration value="BMW"/> </xs:restriction>

type="carType"/>

<xs:simpleType name="carType">

the type "carType" can be used by other elements

series of numbers or letters that can be used, we would use the pattern constraint.

<xs:restriction base="xs:string"> <xs:pattern value="[a-z]"/>

<xs:pattern value="male|female"/>

The whiteSpace constraint is set to "preserve", which means that the XML processor WILL NOT remove any white space characters:

<xs:whiteSpace value="preserve"/>

The whiteSpace constraint is set to "replace", which means that the XML processor WILL REPLACE all white space characters (line feeds, tabs, spaces, and carriage returns) with spaces:

<xs:whiteSpace value="replace"/>

<xs:length value="8"/>

<xs:minLength value="5"/> <xs:maxLength value="8"/>

Constraint Description enumeration Defines a list of acceptable values fractionDigits Specifies the maximum number of decimal places allowed. Must be equal to or greater than zero length Specifies the exact number of characters or list items allowed. Must be equal to or greater than zero maxExclusive Specifies the upper bounds for numeric values (the value must be less than this value) maxInclusive Specifies the upper bounds for numeric values (the value must be less than or equal to this value) maxLength Specifies the maximum number of characters or list items allowed. Must be equal to or greater than zero minExclusive Specifies the lower bounds for numeric values (the value must be greater than this value) minInclusive Specifies the lower bounds for numeric values (the value must be greater than or equal to this value) minLength Specifies the minimum number of characters or list items allowed. Must be equal to or greater than zero 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 (line feeds, tabs, spaces, and carriage returns) is handled

Attributes are optional by default. To specify that the attribute is required, use the "use" attribute: <xs:attribute name="lang" type="xs:string" use="required"/>

<choice> indicator specifies that either one child element or another can occur

The <sequence> indicator specifies that the child elements must appear in a specific order:

Occurrence indicators are used to define how often an element can occur.

For all "Order" and "Group" indicators (any, all, choice, sequence, group name, and group reference) the default value for maxOccurs and minOccurs is 1.

The <maxOccurs> indicator specifies the maximum number of times an element can occur:

The <minOccurs> indicator specifies the minimum number of times an element can occur:

To allow an element to appear an unlimited number of times, use the maxOccurs="unbounded" statement:

Group indicators are used to define related sets of elements.

<xs:group name="groupname">

After you have defined a group, you can reference it in another definition

<xs:group name="persongroup">

<xs:group ref="persongroup"/>

<xs:attributeGroup name="groupname">

<xs:attributeGroup ref="personattrgroup"/>

A "Valid" XML document also conforms to a DTD. A "Valid" XML document is a "Well Formed" XML document, which also conforms to the rules of a Document Type Definition (DTD):

Valid XML Documents A "Valid" XML document is a "Well Formed" XML document, which also conforms to the rules of a Document Type Definition (DTD):

XML Schema is an XML based alternative to DTD.

XML Schema  W3C supports an XML based alternative to DTD called XML Schema: