newbie question: ref or complex type ?

[Sol Mayer-Orn]

I have an XML document, with one structure nested inside another - e.g "manager" element nested inside a "company":

<company>
<manager>
<name> john </name>
</manager>
</company>

I'm trying to create a schema (xsd) for this.
Note my "manager" needs to be defined outside the scope of "company", so that it's re-usable (i.e. manager may be nested inside other structures, not just "company").
I get the impression there are 2 ways to do it:
1. Define "manager" as *element*, then let "company" declare a *ref* to it

<schema ...>
<element name="company">
<complexType>
<sequence>
<element ref="manager"/>
</sequence>
</complexType>
</element>
<element name="manager">
<complexType>
<sequence>
<element name="name" type="string"/>
</sequence>
</complexType>
</element>
</schema>

2. Define "manager" as *complex type*

<schema ...>
<element name="company">
<complexType>
<sequence>
<element name="manager" type="managerType"/>
</sequence>
</complexType>
</element>
<complexType name="managerType>
<sequence>
<element name="name" type="string"/>
</sequence>
</complexType>
</schema>

Could anyone please tell what's the difference between the 2 approaches ? Why does XML define 2 syntaxes to achieve the same goal ?
Thanks

[Madhav Lakkapragada]

This feature provides an easy way of declaring element-types that are used multiple times in the Schema. You have only one global declaration and use the ref attribute in other local element declarations to reference the definition of the global element.

Say you want to associate an address to your XML example. The company has an address of its own. The manager may have multiple addresses - work and home and as such each employee of the company has another address, which could be different. To acheive this, you declare a global element called address with a type and then use the ref attribute to refer to that type.
Hope this helps...

- m

[Sol Mayer-Orn]

Thanks very much for your reply.
It's just that I thought that the same thing (reusable elements) can be achieved with "complexType" ... when would you use "complexType", and when would you prefer "ref" to an element ?

Thanks again.

[Hari Vignesh Padmanaban]

"In general, the value of the ref attribute must reference a global element, i.e. one that has been declared under schema rather than as part of a complex type definition"

So

 
<xs:element name="Company">
 <xs:complexType>
<xs:sequence>
  <xs:element name="manager" ref="managerType"/>
</xs:sequence>
 </xs:complexType>
</xs:element>
 
<xs:complexType name="managerType">
<xs:sequence>
<xs:element name="name" type="xs:string"/>
</xs:sequence>
</xs:complexType>
 
 

is not possible
[ August 04, 2005: Message edited by: Hari Vignesh Padmanaban ]

[Hari Vignesh Padmanaban]

Originally posted by Sol Mam-Orn:
Thanks very much for your reply.
It's just that I thought that the same thing (reusable elements) can be achieved with "complexType" ... when would you use "complexType", and when would you prefer "ref" to an element ?

Thanks again.

Well complex typoes have a lot of features that go along with them

It is possible to achieve "inheritance" through defining complex types using the <xs:extension> attribute

It is possible to choose (or restrict) definitions in a complex type using the <xs:restriction> attribute

You can make a complex type abstrat using the abstract attribute

You can also make complex types final by using the final attribute

And you cant do any of this with <xs:element>

Hope that helps

[ August 04, 2005: Message edited by: Hari Vignesh Padmanaban ]

Just to clear things up,

When you use <complexType> inside teh definition of an element, rather than as a seprate definition, like

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

you cant

Give it a name

Use the final or abstract attributes

Resue it across several schemas

hth
[ August 04, 2005: Message edited by: Hari Vignesh Padmanaban ]

[Madhav Lakkapragada]

Originally posted by Hari Vignesh Padmanaban:
"In general, the value of the ref attribute must reference a global element, i.e. one that has been declared under schema rather than as part of a complex type definition"

So

 
<xs:element name="Company">
 <xs:complexType>
<xs:sequence>
  <xs:element name="manager" ref="managerType"/>
</xs:sequence>
 </xs:complexType>
</xs:element>
 
<xs:complexType name="managerType">
<xs:sequence>
<xs:element name="name" type="xs:string"/>
</xs:sequence>
</xs:complexType>
 
 

is not possible

Well, this is NOT possible under the assumed condition that the parent of the complexType is NOT the schema element ie; the complexType named managerType is NOT a global definition.

Or am I way off......

- m

[Hari Vignesh Padmanaban]

 
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="unqualified">
<xs:element name="company">
<xs:complexType>
<xs:sequence>
  <xs:element  name="manager" type="managerType"/>
  <xs:element name="programmer"/>
</xs:sequence>
</xs:complexType>
</xs:element>


<xs:complexType name="managerType">
<xs:sequence>
<xs:element name="name" type="xs:string"/>
</xs:sequence>
</xs:complexType>

        <xs:element name="test">
<xs:complexType>
<xs:sequence>
<xs:element ref="company"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>
 
  

As you can see,

<xs:complexType name="managerType">

is declared under teh schema element If you change

 <xs:element  name="manager" type="managerType"/> 

to

 <xs:element  name="manager" ref="managerType"/> 

the parser will still complain ( I am using XmlSpy IDE)

but the following lines

<xs:element ref="company"/>
  

in the

<xs:element name="test">  

works !!!

and changing

<xs:element ref="company"/>
  

to

<xs:element ref="programmer"/>

does not work as expected !!



hmm seems like more investigation has to be done ..meanwhile any XML experts are welcome to suggest your ideas

And the lines ""In general, the value of the ref attribute must reference a global element, i.e. one that has been declared under schema rather than as part of a complex type definition" were quoted from W3C specs !!

mabe teh last lines should be "one that has been declared under schema rather than as part of a complex type definition or not a complex type definition"


HTH
[ August 06, 2005: Message edited by: Hari Vignesh Padmanaban ]