XML Schema

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Chapter 04 Chapter 04

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XML Schema 2

Agenda

Schema characteristics

Element Declaration

Simple Element

Restrictions

Complex Elements

Indicator

Namespaces

Schema characteristics

Element Declaration

Simple Element

Restrictions

Complex Elements

Indicator

Namespaces

XML Schema 3

XML Schema

“Schema” è un termine generale, dal vocabolario inglese: “a structured framework or plan”

Quando si parla di “XML Schema” si intende usualmente il W3C XML Schema Language … e il suo acronimo XSD (Xml Schema Definitiom)

DTD, XML Schema, e RELAX NG sono tutti linguaggi di “schema” XML

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Very Simple xml schema

It starts with an XML declaration L’estensione è .xsd e l’elemento root è <schema> Namespace declaration Element Declaration

The declaration makes use of our Schema namespace, and it uses attributes to provide information about the element we are defining

XML SCHEMA ARE WELL_FORMED XML DOCUMENTS

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Schema characteristics

Because XML Schemas are written using XML, that allows Schemas to be adopted quickly and easily by applications already using XML.

Because XML is text based, it is easily transferable via common Internet file transfer methods, such as FTP and HTTP.

In fact, Schemas are "optimized for interoperability" in this way because they are recursive, self-describing documents.

XML Schemas is for datatyping.Datatypes allow you to specify that a piece of information has to be in a specific data format. Datatypes are a very powerful mechanism for placing

constraints on your XML documents.

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Element Declarations

The declaration uses the element type, which has a number of attributes that manipulate properties of the element.

In the preceding declaration, there is a name attribute, which is used to specify the name of the element type being declared.

There is also a type attribute, which is how you specify the datatype associated with an element using XML Schema.

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Valid Attributes for tag <element>

The element declaration in an XML Schema takes the form of the <element> tag.

That tag forms the start of any element declaration in your schema.

The <element> declaration can accept a number of attributes, each one designed to manipulate one or more of the properties that make up an element declaration.

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Default and Fixed attribute

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MaxOccurs and MinOccurs attribute

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REF and Type attribute

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Content Models: Elementi “semplici” e “complessi”

Un elemento semplice contiene solo testo Non ha attributi Non contiene altri elementi Non può essere vuoto Ci possono essere varie restrizioni applicate al

contenuto

Un elemento complesso Può avere attributi Può essere vuoto, contenere testo, altri elementi, o

sia testo che altri elementi.

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Definire un elemento semplice

Un elemento semplice è definito come:

<xs:element name="name” type="type” /> dove:

name è il nome dell’elemento Valori comuni per type sono

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

<xs:element name="quantity" type="xs:integer"/>

<xs:element name="temperature" type="xs:decimal"/>

<xs:element name="holiday" type="xs:date"/>

<xs:element name="attendance" type="xs:boolean"/>

<xs:element name="title" type="xs:string"/>

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Definire un attributo

Gli attributi sono dichiarati sempre come tipi semplici Definito come

<xs:attribute name="name” type="type” />

dove: name e type sono gli stessi che per xs:element

Altri attributi che gli elementi semplici possono avere: default="default value" se nessun valore è specificato fixed="value” nessun altro valore può essere specificato use="optional" non richiesto (default) use="required" richiesto

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<simpleType>

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Restrizioni (“facets”)

La forma generale delle restrizioni è: <xs:element name="name"> (o

xs:attribute) <xs:restriction base="type"> ... the restrictions ... </xs:restriction></xs:element>

Ad esempio: <xs:element name="age">

<xs:restriction base="xs:integer"> <xs:minInclusive value="0"> <xs:maxInclusive value="140"> </xs:restriction></xs:element>

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Restrizioni su numeri

minInclusive -- numero deve essere ≥ di value

minExclusive -- numero deve essere > di value

maxInclusive -- numero deve essere ≤ di value

maxExclusive -- numero deve essere < di value

totalDigits -- numero deve avere value cifre

fractionDigits -- numero deve avere non più di value

cifre dopo il punto decimale

XML Schema 17

Restrizioni su stringhe

length -- la stringa deve contenere value caratteri minLength -- la stringa deve contenere almeno

value caratteri maxLength -- la stringa deve contenere non più di

value caratteri pattern -- value è una espressione regolare da

soddisfare whiteSpace -- dice come trattare gli spazi bianchi

value="preserve" li mantiene value="replace" rinpiazza con “spazi” value="collapse" rimuove gli spazi iniziali, finali e

rimpiazza le sequenze con uno spazio singolo

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Enumerazioni

Restringe il range di possibili valori ad una loro enumerazione

Esempio: <xs:element name="season">

<xs:simpleType> <xs:restriction base="xs:string"> <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>

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ESEMPIO : writing tip on a pen

if we wanted to create an attribute for the size of the writing tip on a pen, we might want the size to be able to be expressed as a name, such as "Extra Fine" or as a decimal, such as ".05".

size by name size by value

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UNIONE per creare un attributo di nome “SIZE”

Element that use new attribute

Legal value for the size attribute

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Elementi Complessi

Un elemento complesso è definito da: <xs:element name="name">

<xs:complexType> ... information about the complex type... </xs:complexType> </xs:element>

Esempio: <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>

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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

Note: Each of these elements may contain attributes as well!

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Examples 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>John</firstname> <lastname>Smith</lastname> </employee>

A complex XML element, "food", which contains only text:<food type="dessert">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>

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Complex Element Definition: declared directly by naming the element

If you use the method described above, only the "employee" element can use

the specified complex type.

Note that the child elements, "firstname" and "lastname", are surrounded by

the <sequence> indicator. This means that the child elements must appear in

the same order as they are declared.

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Complex Element Definition: have a type attribute that refers to the name of the complex type to use

If you use the method described above, several elements

can refer to the same complex type

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Base a complex element on an existing complex element and add some elements

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Complex Empty Elements

<product prodid="1345" />

Product element declaration :

<xs:element name="product"> <xs:complexType> <xs:attribute name="prodid" type="xs:positiveInteger"/> </xs:complexType></xs:element>

<xs:element name="product" type="prodtype"/>

<xs:complexType name="prodtype"> <xs:attribute name="prodid" type="xs:positiveInteger"/></xs:complexType>

<xs:element name="product" type="prodtype"/>

<xs:complexType name="prodtype"> <xs:attribute name="prodid" type="xs:positiveInteger"/></xs:complexType>

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Complex Type - Elements Only

An "elements-only" complex type contains an element that contains only other elements.

<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>

xs:element name="person" type="persontype"/><xs:complexType name="persontype"> <xs:sequence> <xs:element name="firstname" type="xs:string"/> <xs:element name="lastname" type="xs:string"/> </xs:sequence></xs:complexType>s

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Complex Text-Only Elements

A complex text-only element can contain text and attributes.

<xs:element name="somename"> <xs:complexType> <xs:simpleContent> <xs:extension base="basetype"> .... .... </xs:extension> </xs:simpleContent> </xs:complexType></xs:element>

OR

<xs:element name="somename"> <xs:complexType> <xs:simpleContent> <xs:restriction base="basetype"> .... .... </xs:restriction> </xs:simpleContent> </xs:complexType></xs:element>

Use the extension/restriction element to expand or to limit the base simple type for the element.

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Complex Types With Mixed Content

A mixed complex type element can contain attributes, elements, and text

<letter>Dear Mr.<name>John Smith</name>.Your order <orderid>1032</orderid>will be shipped on <shipdate>2001-07-13</shipdate>.</letter>

<xs:element name="letter"> <xs:complexType mixed="true"> <xs:sequence> <xs:element name="name" type="xs:string"/> <xs:element name="orderid" type="xs:positiveInteger"/> <xs:element name="shipdate" type="xs:date"/> </xs:sequence> </xs:complexType></xs:element>

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Indicator

Order indicators: are used to define the order of the elements All Choice Sequence

Occurrence indicators: are used to define the order of the elements maxOccurs minOccurs

Group indicators: are used to define related sets of elements Group name attributeGroup name

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Order Indicator : ALL

The <all> indicator specifies that the child elements can appear in any order, and that each child element must occur only once

<xs:element name="person"> <xs:complexType> <xs:all> <xs:element name="firstname" type="xs:string"/> <xs:element name="lastname" type="xs:string"/> </xs:all> </xs:complexType></xs:element>

Note: When using the <all> indicator you can set the <minOccurs> indicator to 0 or 1 and the <maxOccurs> indicator can only be set to 1

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Order Indicator : CHOICE

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

<xs:element name="person"> <xs:complexType> <xs:choice> <xs:element name="employee" type="employee"/> <xs:element name="member" type="member"/> </xs:choice> </xs:complexType></xs:element>

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Order Indicator : SEQUENCE

The <sequence> indicator specifies that the child elements must appear 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

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Occurrence Indicator : maxOccurs

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

<xs:element name="person"> <xs:complexType> <xs:sequence> <xs:element name="full_name" type="xs:string"/> <xs:element name="child_name" type="xs:string" maxOccurs="10"/> </xs:sequence> </xs:complexType></xs:element>

The example above indicates that the "child_name" element can occur a minimum of one time (the default value for minOccurs is 1) and a maximum of ten times in the "person" element.

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Occurrence Indicator : minOccurs

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

<xs:element name="person"> <xs:complexType> <xs:sequence> <xs:element name="full_name" type="xs:string"/> <xs:element name="child_name" type="xs:string" maxOccurs="10" minOccurs="0"/> </xs:sequence> </xs:complexType></xs:element>

The example above indicates that the "child_name" element can occur a minimum of zero times and a maximum of ten times in the "person" element.

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

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Working example

<?xml version="1.0" encoding="ISO-8859-1"?><persons xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:noNamespaceSchemaLocation="family.xsd"><person><full_name>Hege Refsnes</full_name><child_name>Cecilie</child_name></person><person><full_name>Tove Refsnes</full_name><child_name>Hege</child_name><child_name>Stale</child_name><child_name>Jim</child_name><child_name>Borge</child_name></person><person><full_name>Stale Refsnes</full_name></person></persons>

<?xml version="1.0" encoding="ISO-8859-1"?><xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"elementFormDefault="qualified"><xs:element name="persons"> <xs:complexType> <xs:sequence> <xs:element name="person" maxOccurs="unbounded"> <xs:complexType> <xs:sequence> <xs:element name="full_name" type="xs:string"/> <xs:element name="child_name" type="xs:string" minOccurs="0" maxOccurs="5"/> </xs:sequence> </xs:complexType> </xs:element> </xs:sequence> </xs:complexType></xs:element></xs:schema>

The XML file contains a root element named "persons". Inside this root element we have defined three "person" elements. Each "person" element must contain a "full_name" element and it can contain up to five "child_name" elements

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Group Indicator : Element/Attribute Group

Element groups are defined with the group declaration, like this:<xs:group name="groupname"> ...</xs:group>

xs:group name="persongroup"> <xs:sequence> <xs:element name="firstname" type="xs:string"/> <xs:element name="lastname" type="xs:string"/> <xs:element name="birthday" type="xs:date"/> </xs:sequence></xs:group>

<xs:element name="person" type="personinfo"/>

<xs:complexType name="personinfo"> <xs:sequence> <xs:group ref="persongroup"/> <xs:element name="country" type="xs:string"/> </xs:sequence></xs:complexType>

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<any> <anyAttribute>

The <any> and <anyAttribute> elements are used to make EXTENSIBLE documents! They allow documents to contain additional elements that are not declared in the main XML schema.

The following example is a fragment from an XML schema called "family.xsd". It shows a declaration for the "person" element. By using the <any> element we can extend (after <lastname>) the content of "person" with any element:

<xs:element name="person"> <xs:complexType> <xs:sequence> <xs:element name="firstname" type="xs:string"/> <xs:element name="lastname" type="xs:string"/> <xs:any minOccurs="0"/> </xs:sequence> </xs:complexType></xs:element>

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Perchè XML Schema?

DTD fornisce specifiche deboli Nessuna restrizione sul contenuto del testo Poco controllo sui contenuti misti (mixed content, text

+ elements) Poco controllo sull’ordinamento degli elementi

DTD è scritto in un formato non-XML Parser separati per DTD e XML

XML Schema Definition Language risolve questi problemi Più controllo su strutture e contenuti XSD è scritto in XML

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Riferirsi ad uno schema

Per la DTD il riferimento va prima del root element:<?xml version="1.0"?><!DOCTYPE rootElement SYSTEM "url"><rootElement> ... </rootElement>

Per l’XML Schema il riferimento va nel root element:<?xml version="1.0"?><rootElement

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" (riferimeno richiesto a XML Schema Instance) xsi:noNamespaceSchemaLocation="url.xsd"> (dove trovare lo Schema definition voluto) ...

</rootElement>

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Specifing Namespaces

Are specified using the xmlns attribute to declare the Namespace with an element. The attribute takes the general form

<element xmlns:prefix="Namespace URI">

the element is the element for which we are declaring the Namespace

The prefix is the prefix we will use with our element names

the Namespace URI is the identifier of the Namespace itself.

The prefix is actually optional—if it is left out, the Namespace declaration is considered the default Namespace, and all the elements in thedocument will be treated as members of that Namespace unless they are marked otherwise.

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Namespace URI

Generally, this takes the form of a URL, which serves as a good unique identifier, because it includes the domain name, and is easily understood by Web-enabled software.

The most common misconception resulting from the use of a URL here is that the URL necessarily points to something, when,in fact, it does not. The URL is simply used as a string to identify the Namespace —it does not necessarily point to any specific document (although it can if you want it to) and there is no syntax or standard for creating a Namespace document to live on your server.

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Single Default Namespace

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Multiple Prefixed Namespaces

To make all the Namespaces in the document require a prefix, we use the same basic structure as declaring a default Namespace, only we add the : prefix to the xmlns attribute

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The advantage of this method is that now both Namespaces are declared globally.

That is because they are declared in the root element, and the default Namespace applies to any element without a prefix in the document.

Because the second Namespace is also declared globally, any element in the document can be made part of that Namespace by appending the prefix.

Default and Prefixed Namespaces

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default Namespace globally, and the secondNamespace declared locally

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list of the Namespaces for some of the technologies discussed