MANAGING INFORMATION (CSCU9T4) LECTURE 3: XML …

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MANAGING INFORMATION (CSCU9T4)

LECTURE 3: XML STRUCTURE 2 - SCHEMAS

Gabriela Ochoa

http://www.cs.stir.ac.uk/~goc/

OUTLINE

Well-formed and Valid XML documents

Document Type Definitions (DTDs)

XML Schemas

Summary

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http://www.cs.stir.ac.uk/~goc/

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XML SCHEMA

Describe the structure of an XML document, just

like a DTD

They became a W3C Recommendation in May

2001

More powerful than DTD because they:

are written in XML

are extensible to additions

support data types

support namespaces

Drawback of Schemas: they are more complex and

verbose than DTD

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ADVANTAGES OF XML SCHEMAS

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Easier to:

Describe document

content

Define restrictions on

data

Validate the

correctness of data

Convert data between

different data types

No need to learn a

new language

You can use the same

tools for documents

and Schema

Editor

Parser

Validation

Transformation

Support for Data Types Written in XML

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XML SCHEMA- SIMPLE

EXAMPLE <xs:element name="note"> <xs:complexType> <xsd: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:element name="note"> defines the element called "note"

<xs:complexType> the "note" element is a complex type

<xs:sequence> the complex type is a sequence of elements

<xs:element name="to" type="xs:string"> the element "to" is of type string (text)

<xs:element name="from" type="xs:string"> the element "from" is of type string

<xs:element name="heading" type="xs:string"> the element "heading" is of type string

<xs:element name="body" type="xs:string"> the element "body" is of type string

<?xml version="1.0"?> <note> <to>Tove</to> <from>Jani</from> heading>Reminder</heading> <body>Don't forget me this weekend!</body> </note>

Note: I’m omitting the

heading to make it simple

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Book.xml

1 <?xml version = "1.0"?>

2 

3 

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5 <deitel:books xmlns:deitel = "http://www.deitel.com/booklist">

6 <book>

7 <title>XML How to Program</title>

8 </book>

9 <book>

10 <title>C How to Program</title>

11 </book>

12 <book>

13 <title>Java How to Program</title>

14 </book>

15 <book>

16 <title>C++ How to Program</title>

17 </book>

18 <book>

19 <title>Perl How to Program</title>

20 </book>

21 </deitel:books>

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Book.xsd

1 <?xml version = "1.0"?>

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3 

4 

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6 <xs:schema xmlns:xsd = "http://www.w3.org/2000/10/XMLSchema"

7 xmlns:deitel = "http://www.deitel.com/booklist"

8 targetNamespace = "http://www.deitel.com/booklist">

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10 <xs:element name = "books" type = "deitel:BooksType"/>

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12 <xs:complexType name = "BooksType">

13 <xs:element name = "book" type = "deitel:BookType"

14 minOccurs = "1" maxOccurs = "unbounded"/>

15 </xs:complexType>

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17 <xs:complexType name = "BookType">

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

19 </xs:complexType>

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21 </xs:schema>

Attributes name and type specify the element’s

name and data type, respectively.

Element complexType defines an element type

that has a child element named book.

Attribute maxOccurs, with value unbounded

specifies that books may have any number of book

child elements.

Attribute minOccurs specifies that books must

contain a minimum of one book element.

Element element defines an element to be

included in the XML document structure.

XML SCHEMA DETAILS • The <schema> Element

• ELEMENTS

• ATTRIBUTES

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THE <SCHEMA> ELEMENT

The root element of every XML Schema

It may contain some attributes

<?xml version="1.0"?>

<xs:schema>

...

...

</xs:schema>

<?xml version="1.0"?>

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

targetNamespace="http://www.w3schools.com"

xmlns="http://www.w3schools.com"

...

...

</xs:schema>

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

• Elements and data types come from the "http://www.w3.org/2001/XMLSchema" namespace.

• Elements and data types in the scheme should be prefixed with xs:

targetNamespace=http://www.w3schools.com

• Elements defined by this schema come from the "http://www.w3schools.com" namespace.

xmlns=http://www.w3schools.com

• The default namespace is "http://www.w3schools.com".

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ELEMENTS

Elements are the main building block of all XML documents,

containing the data and determine the structure of the instance

document.

Syntax: <xs:element name="x" type="y"/>

Name property: tag name that will appear in the XML document

Type property: provides the description of what type of data can be

contained within the element when it appears in the XML document.

Element content type can be:

Simple: simple predefined data types (such as: xs:string, xs:decimal,

xs:integer, xs:boolean, xs:date, xs:time)

Complex: other elements

Mixed: both (simple data types an other elements)

User defined types: using the <xs:simpleType> and

<xs:complexType> constructs, which we will cover later.

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EXAMPLES OF SIMPLE ELEMENTS AND

THEIR XML DATA

Sample XSD Sample XML

<xs:element name="Customer_dob“ type="xs:date"/>

<Customer_dob> 2000-01-12T12:13:14Z </Customer_dob>

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

<Customer_address> 99 London Road </Customer_address>

<xs:element name="OrderID“ type="xs:int"/>

<OrderID> 5756 </OrderID>

<xs:element name="Body“ type="xs:string"/>

<Body> (a type can be defined as a string but not have any content, this is not true of all data types however).</Body>

Note: the corresponding value in the XML document must be in the correct

format for its given type otherwise this will cause a validation error.

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FIXED AND DEFAULT PROPERTIES

The valid data values for the element in the XML

document can be further constrained using the fixed and

default properties.

Default: if no value is specified in the XML document then the

application reading the document, should use the default specified

in the XSD.

Fixed: the value in the XML document can only have the value

specified in the XSD

Example:

<xs:element name="Customer_name" type="xs:string" default="unknown"/>

<xs:element name="Customer_location" type="xs:string" fixed="UK"/>

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CARDINALITY CONSTRAINTS

Use to indicate the specific number of elements that can

appear in an XML document

Use minOccurs and maxOccurs attributes

Specify whether an element is mandatory, optional, or can

appear up to a set number of times.

Default values for minOccurs and maxOccurs is 1. So if not

present, the element must appear once.

minOccurs can be assigned any non-negative integer value

(e.g. 0, 1, 2, 3... etc.)

maxOccurs can be assigned any non-negative integer value

or the special string constant "unbounded" meaning there

is no maximum so the element can occur an unlimited

number of times.

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CARDINALITY CONSTRAINTS: EXAMPLES Sample XSD Description

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

If we do not specify minOccurs or maxOccurs, then the default values of 1 are used. This means there has to be one and only one occurrence of Customer_dob, i.e. it is mandatory.

<xs:element name="Customer_order" type="xs:integer" minOccurs ="0" maxOccurs="unbounded"/>

If we set minOccurs to 0, then the element is optional. Here, a customer can have from 0 to an unlimited number of Customer_orders.

<xs:element name="Customer_hobbies" type="xs:string" minOccurs="2" maxOccurs="10"/>

Setting both minOccurs and maxOccurs means the element Customer_hobbies must appear at least twice, but no more than 10 times. 14

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COMPLEX TYPES

A complex type is a container for other element definitions,

this allows you to specify which child elements an element can

contain.

Let us consider some simple element definitions:

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

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

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

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

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

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

Some of these elements should really be represented as child elements:

• "Customer_dob" and "Customer_address" belong to a parent element

"Customer".

• "Supplier_phone" and "Supplier_address" belong to a parent element

"Supplier". 15

<xs:element name="Customer">

<xs:complexType>

<xs:sequence>

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

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

</xs:sequence>

</xs:complexType>

</xs:element>

<xs:element name="Supplier">

<xs:complexType>

<xs:sequence>

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

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

</xs:sequence>

</xs:complexType>

</xs:element>

<Customer>

<Dob> 2000-01-12T12:13:14Z </Dob>

<Address> 34 thingy street, someplace, sometown, w1w 8uu </Address>

</Customer>

<Supplier>

<Phone>0123987654</Phone>

<Address>22 whatever place, someplace, sometown, ss1 6gy </Address>

</Supplier>

Example of complex types

• 2 new element type: “Customer” and “Supplier”

• <xs:complexType>: a container for other <xs:element > definitions

• <xs:element > contains <xs:sequence> which in turn has child elements

Example XML

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TYPE COMPOSITORS

There are three types of compositors <xs:sequence>,

<xs:choice> and <xs:all>

Determine how the child elements contained within them will

appear within the XML document.

Compositor Description

Sequence The child elements in the XML document MUST appear in

the order they are declared in the XSD schema.

Choice Only one of the child elements described in the XSD schema

can appear in the XML document.

All The child elements described in the XSD schema can appear

in the XML document in any order.

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<xs:complexType>

<xs:sequence>

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

<xs:element name="Address">

<xs:complexType>

<xs:sequence>

<xs:element name="Line1" type="xs:string" />


</xs:sequence>

</xs:complexType>

</xs:element>

</xs:sequence>

</xs:complexType>

</xs:element>

<xs:element name="Supplier">

<xs:complexType>

<xs:sequence>

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

<xs:element name="Address">

<xs:complexType>

<xs:sequence>



</xs:sequence>

</xs:complexType>

</xs:element>

</xs:sequence>

</xs:complexType>

</xs:element>

Example:

Break the ‘Address’

into several fields.

More useful in

practice

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<xs:complexType name="AddressType">

<xs:sequence>

<xs:element name="Line1" type="xs:string"/>

<xs:element name="Line2" type="xs:string"/>

</xs:sequence>

</xs:complexType>

• It makes more sense to have a

single definition for "Address",

which could then be used by both

customer and supplier.

• This can be done by defining a complexType independently of an

element, and giving it a unique

name.

GLOBAL TYPES


<xs:complexType>

<xs:sequence>

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

<xs:element name="Address" type="AddressType"/>

</xs:sequence>

</xs:complexType>

</xs:element>

<xs:element name="supplier">

<xs:complexType>

<xs:sequence>

<xs:element name="address" type="AddressType"/>

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

</xs:sequence>

</xs:complexType>

</xs:element>

We can now use

the new

AddressType

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EXAMPLE XML

<Customer>

<Dob> 2000-01-12T12:13:14Z </Dob>

<Address>

<Line1>34 thingy street, someplace</Line1>

<Line2>sometown, w1w8uu </Line2>

</Address>

</Customer>

<Supplier>

<Phone>0123987654</Phone>

<Address>

<Line1>22 whatever place, someplace</Line1>

<Line2>sometown, ss1 6gy </Line2>

</Address>

</Supplier>

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ATTRIBUTES

An attribute provides extra information within an element

Attributes have name and type properties. Syntax:

<xs:attribute name="x" type="y"/>

Attributes are either optional or mandatory (default is optional)

The "use" property is used to specify if the attribute is optional

or mandatory.

The default and fixed attributes can be specified within the XSD

attribute specification (in the same way as they are for

elements).

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ATTRIBUTES: EXAMPLES

Sample XSD Sample XML

<xs:element name="Order">

<xs:complexType>

<xs:attribute name="OrderID"

type="xs:int"/>

</xs:complexType>

</xs:element>

<Order OrderID="6"/>

or

<Order/>


<xs:complexType>


type="xs:int"

use="optional"/>

</xs:complexType>

</xs:element>


or

<Order/>


<xs:complexType>


type="xs:int"

use="required"/>

</xs:complexType>

</xs:element>


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SUMMARY

More Examples: http://www.w3schools.com/schema/schema_example.asp

Two ways of describing the structure of an XML

document

Document Type Definitions (DTDs)

<!DOCTYPE root_element >

<!ELEMENT name allowable_contents>

<ATTLIST el_name att_name att_type default_value >

XML Schemas

<schema>

<xs:element name="x" type="y"/>

<xs:attribute name="x" type="y"/>

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http://www.w3schools.com/schema/schema_example.asp

http://www.w3schools.com/schema/schema_example.asp

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