xml 2nd edition tutorial 4 working with schemas. xp schemas a schema is an xml document that defines...

XML2nd EDITION

Tutorial 4Working With Schemas

XPXPXPXPXPSchemas• A schema is an XML document that defines the

content and structure of one or more XML documents.

• The XML document containing the content is called the instance document.

XPXPXPXPXPComparing Schemas and DTDs

This figure compares schemas and DTDs

XPXPXPXPXPSchema Vocabularies• There is no single schema form. Several schema

“vocabularies” have been developed in the XML language.

• Support for a particular schema depends on the XML parser being used for validation.

XPXPXPXPXPSchema Vocabularies

This figure shows a few schema vocabularies

XPXPXPXPXPStarting A Schema File• A schema is always placed in a separate XML

document that is referenced by the instance document.

XPXPXPXPXPExample Schema <?xml version="1.0"?>

< xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

<xs:element name="note"> <xs:complexType> <xs:sequence> <xs:element name="to" type="xs:string"/> <xs:element name="from" type="xs:string"/> <xs:element name="heading" type="xs:string"/> <xs:element name="body" type="xs:string"/> </xs:sequence> </xs:complexType>< /xs:element>

< /xs:schema>

XPXPXPXPXPElements And Attributes Of The Patients Document

This figure shows the elements and attributes of the patients.xml document

XPXPXPXPXPSchema Types• XML Schema recognize two categories of types:– Simple type contains only a single value

• Value of an attribute• Or the textual content of an element

– Complex type• Contains a structure

XPXPXPXPXPSchema TypesThis figure shows types of elements

XPXPXPXPXPSimple Type Elements• Use the following syntax to declare a simple type

element in XML Schema:

<element name=“name” type =“type”/>

name = the name of the element in the instance document

type = the data type of the element.

• Example:<xs:element name = “lastName” type = “xs:string” />

Unlike DTD, schema isan XML language

XPXPXPXPXPUnderstanding Data Types• XML Schema supports two data types– A built-in data type is part of the XML Schema

specifications and is available to all XML Schema authors.

– A user-derived data type is created by the XML Schema author for specific data values in the instance document.

XPXPXPXPXPDeclaring An Attribute• An attribute is another example of a simple type. The syntax

to define an attribute is<xs:attribute name=“name” type="type” default=“default”

fixed=“fixed” />name = the name of the attributetype = the data typedefault = the attribute’s default valuefixed = a fixed value for the attribute

• For examle:<xs:attribute name=“Gender” type=“xs:string”

default=“female” />

XPXPXPXPXPAssociating Attributes And Elements• The basic structure for defining a complex type with

XML Schema is<xs:element name="name">

<xs:complexType>declarations

</xs:complexType></xs:element>

name = the name of the element declarations = schema commands specific to the type of

complex element being defined.

XPXPXPXPXPAssociating Attributes And Elements• Four complex type elements that usually

appear in an instance document are the following:– The element is an empty element and contains

only attributes.– The element contains textual content and

attributes but no child elements.– The element contains child elements but not

attributes.– The element contains both child elements and

attributes.

XPXPXPXPXPEmpty Elements And Attributes• The code to declare the attributes of an empty element is<xs:element name="name">

<xs:complexType>attributes

</xs:complexType></xs:element>

attributes = the set of declarations that define the attributes associated with the element

XPXPXPXPXPEmpty Elements And Attributes• For example:

<xs: element name=“subject”><xs:complexType>

<xs:attriubute name=“name” type=“xs:string” />

<xs:attriubute name=“age” type=“xs:string” /></xs: complexType>

</xs:element>• Describes the following empty element:

<subject name=“Cynthia Dibbs” age=“62” />

XPXPXPXPXPSimple Content And Attributes• If an element is not empty and contains textual content (but

no child elements), the structure of the complex type element is slightly different.

<xs:element name="name"><xs:complexType>

<xs:simpleContent><xs:extension base="type">

attributes</xs:extension>

</xs:simpleContent></xs:complexType>

</xs:element>

XPXPXPXPXPSimple Content And Attributes• For example:

<xs:element name=“performance”><xs:complexType>

<xs:simpleContent> <xs:extension base=“xs:string”>

<xs:attribute name=“scale” type=“xs:string”/> </xs:extension></xs:simpleContent>

</xs:complexType></xs:element>

• defines• <performance scale=“Karnofskyk”>0.81</performance>

XPXPXPXPXPSpecifying The Use Of An Attribute• An attribute may or may not be required with a

particular element. To indicate whether an attribute is required, you add the use attribute to the element declaration or reference. The use attribute has the following values:– required—The attribute must always appear with the

element– optional—(default) The use of the attribute is optional with

the element– prohibited—The attribute cannot be used with the element

• For example, the previous attribute declaration is modified as:<xs:attribute name=“scale” type=“xs:string” use=“required”/>

XPXPXPXPXPReferencing An Element Or Attribute• Rather than nesting the attribute declaration within

the element, you can create a reference to it. The code to create a reference to an element or attribute declaration is<xs:element ref="elemName" /><xs:attribute ref="attName" />

whereelemName = the name used in an element declarationattName = the name used in an attribute declaration

XPXPXPXPXPReferencing An Element Or Attribute<xs:attribute name=“scale” type=“xs:string” />

<xs:element name=“performance”><xs:complexType>

<xs:simpleContent><xs:extension base = “xs:string>

<xs:attribute> ref=“scale” use=“required” />

</xs:extension></xs:simpleContent>

</xs:complexType></xs:element>

XPXPXPXPXPWorking With Child Elements• Another kind of complex type element contains child

elements, but no attributes. To define these child elements, use the code structure<xs:element name="name">

<xs:complexType><xs:compositor>

elements</xs:compositor>

</xs:complexType></xs:element>

whereelements =the list of simple type element declarations for

each child elementcompositor = defines how the child elements are organized.

XPXPXPXPXPUsing Compositors• XML Schema supports the following compositors:– sequence defines a specific order for the child

elements– choice allows any one of the child elements to

appear in the instance document– all allows any of the child elements to appear in

any order in the instance document; however, they must appear either only once or not all.

XPXPXPXPXPUsing Compositors<element name=“address”>

<xs:complexType><xs:sequence>

<xs:element name = “street” type = “xs:string”/>

<xs:element name = “city” type = “xs:string”/><xs:element name = “state” type = “xs:string”/>

</xs:sequence><xs:complexType>

</element>

Must be in sequence

XPXPXPXPXPUsing Compositors<element name=“Family”>

<xs:complexType><xs:all>

<xs:element name = “Father” type = “xs:string”/>

<xs:element name = “Mother” type = “xs:string”/>

</xs:all><xs:complexType>

</element>

Family may contain Father and/or Mother in no

particular order

XPXPXPXPXPSpecifying The Occurrences Of An Item• <xs:element name=“patient” type=“xs:string”

minOccurs=“1” maxOccurs=“3”/>

XPXPXPXPXPWorking With Child Elements And Attributes• The code for a complex type element that contains

both attributes and child elements is<xs:element name="name">

<xs:complexType><xs:compositor>

elements</xs:compositor>

</xs:complexType>attributes

</xs:element>

XPXPXPXPXPChild Elements And Attributes Example<xs:element name=“patient”> <xs:complexType> <xs:sequence> <xs:element ref=“lastname”/> <xs:element ref=“firstName”/> </xs:sequence> <xs:attribute ref=“patID use=“required”> </xs:complexType><xs:element>

XPXPXPXPXPSpecifying Mixed Content<Summary>

Patient <Name>Cynthia Davis</Name> was enrolled inthe <Study>Tamoxifen Study</Study> on 8/15/2003.

</Summary>

can be declared in the schema file using the following complex type:

<element name="Summary"><complexType mixed="true">

<sequence><element name="Name" type="string"/><element name="Study" type="string"/>

</sequence></complexType>

</element> element contains both text and child

elements

XPXPXPXPXPApplying A Schema• To attach a schema to the document, you must do

the following:– Declare a namespace for XML Schema in the instance

document.– Indicate the location of the schema file.

• Example:xmlns:xsi=http://www.w3.org/2001/XMLSchema-

instancexsi=SchemaLocation=“pschema.xsd”>

Commonly used for XML Schema

instances

Schema instance namespace

XPXPXPXPXPUnderstanding Data Types• A primitive data type, also called a base type, is one

of 19 fundamental data types not defined in terms of other types.

• A derived data type is a collection of 25 data types that the XML Schema developers created based on the 19 primitive types.

XPXPXPXPXPUnderstanding Data Types

This figure shows the 44 built-in data types

Page XML 168

Premitivetypes

DerivedTypes

Dates & times

XPXPXPXPXPUnderstanding Data Types

This figure shows a partial description of XML string data types

XPXPXPXPXPUsing Data TypesExamples:<xs:attribute name=“patID” type=“xs:ID” /><xs:attribute name=“onStudy” type=“xs:string” /><xs:attribute name=“scale” type=“xs:string” />

XPXPXPXPXPUnderstanding Data Types

This figure shows a partial description of XML numeric data types

XPXPXPXPXPUnderstanding Data Types

This figure shows a partial description of XML date and time data types

XPXPXPXPXPDeriving New Data Types• Three components are involved in deriving new data

types:– Value space: the set of values that correspond to

the data type.– Lexical space: the set of textual representations of

the value space.– Facets: the properties of the data type that

distinguish one data type from another.• Text string length, range of allowable values,

XPXPXPXPXPUser Derived Data• New data types fall into three categories:– List: a list of values where each list is derived from

a base type.– Union: the combination of two or more data

types.– Restriction: a limit placed on the facet of a base

type.

XPXPXPXPXPList• List data type is a list of values separated by

white space• To create a list data type:

<xs:simpleType name=wbcList”> <xs:list itemType=xs:decimal” /><xs:simpleType>

• To use the data type:<xs:element name=“wbc” type=“wbcList” />

<wbe>15.1 15.8. 20.0 9.3 7.1 5.2 </wbc>

XPXPXPXPXPDeriving A Restricted Data Type• The most common way to derive a new data type is

to restrict the properties of a base type. XML Schema provides twelve constraining facets for this purpose.

XPXPXPXPXPConstraining FacetsThis figure shows the 12 constraining facets

XPXPXPXPXPConstraining Facets Example<xs:simpleType name=“ageType”>

<xs:restriction base=“xs:integer”><xs:minInclusive value = “21” />

</xs:restriction></xs:simpleType>

Constrains the data type to be greater than

or equal to the value

XPXPXPXPXPThe Patterns Facet• A pattern can be created with a formatted text string

called a regular expression or regex. • To apply a regular expression in a data type, you use

the code<xs:simpleType name="name">

<xs:restriction base="type"><xs:pattern value="regex"/>

</xs:restriction></xs:simpleType>• Where regex is a regular expression pattern.

XPXPXPXPXPRegular Expressions• Figure 4-30 page 184 shows character types, for

example– \d a digit from 0 to 9– \D non digit character– Etc.

• Figure 4-31 page 185 shows character sets, for example– [chars] Match any character in the chars list– [a-z] Match any lower case letter– [0-9] match any digit form 0-9– Etc.

XPXPXPXPXPPattern Quantifiers

This figure shows pattern quantifiers

XPXPXPXPXPExample Regular Expressions• <xs:pattern value=“\d{3}” />• <xs:pattern value=“[A-Z]*” />• <xs:pattern value=“[A-Z]{0,10}*” /}

<xs:ximpleType name=“mrType”> <sx:restrictiion base=“xs:ID”> <xs:pattern value=“MR\d{3}-\d{3}-d2{2}” /> </xs:restriction><xs:simpleType>

XPXPXPXPXPWorking With Named Types• Schema authors can create customized complex types.

– Advantage: reuse the complex structure in several places in the document.

• For example:<xs:element name=“fullName">

<xs:complexType><xs:sequence>

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

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

</xs:sequence></xs:complexType>

</xs:element>• Use

<xs:element name=“client” type=“fullName”/><xs:element name=“salesperson” type=“fullName”/>

XPXPXPXPXPNamed Model Groups• A named model group is a collection, or group, of

elements. • Syntax

<xs:group name="name">elements

</xs:group>• Where name is the name of the model group, and

elements is a collection of element declarations

XPXPXPXPXPNamed Model Groups Example• Definition

<xs:group name=“fullName”><xs:sequence>

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

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

</xs:sequence></xs:group>

• Use<xs:element name=“client">

<xs:complexType><xs:group ref=“fullName”/>>

</xs:complexType></xs:element>

XPXPXPXPXPWorking With Named Attribute Groups• Attributes can be grouped into collections called

named attribute groups.• This is particularly useful for attributes that you want

to use with several different elements in a schema. The syntax for a named attribute group is

<xs:attributeGroup name="name">attributes

</xs:attributeGroup>• Where name is the name of the attribute group and

attributes is a collection of attributes assigned to the group.

XPXPXPXPXPWorking With Named Attribute Groups• Example:<xs:attributeGroup name=“DRInfo”> <xs:attribute name=“DRID” type=“xs:string” use=“required” /> <xs:attribute name=“dept” type=“xs:string” use=“required” /><xs:attributeGroup>

<xs:element name=“doctor” type=“deptData”/><xs:complexType name = “deptData”> <xs:simplecontent> <xs: extension base = “string”> <xs:attributegroup ref=“DRIinfo”/> </xs:extenson> </xs:simplecontent></xs:complexType>

<doctor DRID=“DR251” dept=“Pediatrics”> curt Hurley<doctor>

XPXPXPXPXPScope• An item has global scope = it is a child of a root

schema element– Can be referenced and reused anywhere in the schema

• An item has local scope = it is nested within another element– Can be referenced and reused only within the item in

which it is declared

XPXPXPXPXPStructuring A Schema• Schemas can be structured in several ways:• Flat catalog (also called salami slice)– All declarations are made globally

• Russian doll– Has only one global element– Everything else is nested inside of that element

• Venetian Blind Design– Similar to flat catalog, except– Creates types and references within a single global element

XPXPXPXPXPStructuring A Schema• One schema design is a Flat Catalog Design.– Sometimes called salami slice design

• In this design, all element declarations are made globally.

• The structure of the instance document is created by referencing the global element declarations.

XPXPXPXPXPFlat Catalog DesignThis figure shows a Flat Catalog design

XPXPXPXPXPStructuring A Schema• Schemas can be structured in a number of ways. One

structure is called a Russian Doll design. This design involves sets of nested declarations.

• While this design makes it easy to associate the schema with the instance document, it can be confusing and difficult to maintain.

XPXPXPXPXPRussian Doll DesignThis figure shows a Russian Doll design

XPXPXPXPXPVENETIAN BLIND DESIGN• A Venetian blind design • Compromise between flat catalogs and

Russian dolls– Element and attribute groups and named types

are declared globally (and can be reused throughout the schema)

– Elements and attributes for the instance document are local and nested

XPXPXPXPXPVenetian Blind Design

XPXPXPXPXPComparing Schema DesignsThis figure compares the three schema designs

XPXPXPXPXPPlacing A Schema In A Namespace: Targeting A Namespace• To associate a schema with a namespace– declare the namespace

prefix:xmlns="uri"– make that namespace the target of the schema.

targetNamespace="uri"• Where

prefix = prefix of the XML Schema namespace uri = URI of the target namespace

XPXPXPXPXPPlacing A Schema In A Namespace: Targeting A Namespace• Example (Figure 4-40):<xs:schema xmlns:xs=http://www.ww3.org/2001/XMLSchema xmlns=“http:/uhosp.edu/patients/na” targetNamespace=“http://uhosp.edu/patients/na>

<xs: element name=“patients”> <xs:complexType> <xs:sequence> <xs:element name=“patient” type=“pType” Minoccurs = “1” maxoccurs=“unbounded” /> </xs:sequence> </xs:complexType></xs:element>

…

Declare the namespace

Make the new namespace the target

of the schema

XPXPXPXPXPApplying A Schema To A Document With A Namespace• To apply a schema to a document with a namespace,

add the following attributes to the instance document’s root element:

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="uri schema"• Where uri is the URI of the namespace and schema is

the location and name of the schema file.• All global elements and attributes from the schema

must be qualified in the instance document.

XPXPXPXPXPApplying A Schema To A Document With A Namespace<patients

xmlns:xsi=http://www.W3.org/200/XMLSchema-instance

xmlns=“http://uhosp.edu/patients/ns xsi:schemaLocation=http://uhosp.edu/patients/ns

patvb.xsd>

<patient patID = “MR890-041-02” … ….</patient>

XPXPXPXPXPIncluding And Importing Schemas• To include a schema from the same namespace, add the

following element as a child of the schema element:<xs:include schemaLocation="schema" />

Where schema is the name and location of the schema file.

• To import a schema from a different namespace, use the syntax

<xs:import namespace="uri" schemaLocation="schema" />• Where uri is the URI of the imported schema’s

namespace and schema is the name and location of the schema file.

XPXPXPXPXPReferencing Objects From Other Schemas• Once a schema is imported, any objects it contains with

global scope can be referenced• To reference an object from an imported schema, you

must declare the namespace of the imported schema in the schema element

• You can then reference the object using the ref attribute or the type attribute for customized simple and complex types