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Re: some problems regarding to transforming UML to XML Schema

From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
Date: 15 Jan 2002 09:34:22 +0000
To: xiaofeng.wang@ps.ge.com
Cc: xmlschema-dev@w3.org
Message-ID: <f5bd70crm8x.fsf@cogsci.ed.ac.uk>
xiaofeng.wang@ps.ge.com writes:

> Hello everybody:
> 
> I found a hard time to map inheritance defined in UML to XML Schema.
> Usually, the complex type extension is used for inheritance. Then, two
> issues raised:
> 
> (1) Use <sequence> or <all> ?
> <sequence> specify the order of elements defined in it. But in UML, there is
> no such specification for order. Attributes and associations defined in a
> class may appear in any order. It seems <all> is good choice (??)

If order doesn't signify, then pick an order and enforce it -- use <sequence>.

> (2) How to use <all>
> <all> does provide the flexibility for order. But it has other restrictions.
> It seems hard for me to handle multi-level inheritance defined in UML.
> Reference [1] shows an example for mapping Inheritance defined in UML to XML
> Schema. It looks like:
> 
> 	<xsd:element name = "Address" type = "Address" abstract = "true"/>
> 	<xsd:complexType name = "Address" abstract = "true">
> 		<xsd:all>
> 			<xsd:element name = "name" type = "xsd:string"/>
> 			<xsd:element name = "street" type = "xsd:string"/>
> 			<xsd:element name = "city" type = "xsd:string"/>
> 		</xsd:all>
> 	</xsd:complexType>
> 	<xsd:element name = "USAddress" type = "USAddress" substitutionGroup
> = "Address"/>
> 	<xsd:complexType name = "USAddress">
> 		<xsd:complexContent>
> 			<xsd:extension base = "Address">
> 				<xsd:all>
> 					<xsd:element name = "state" type =
> "xsd:string"/>
> 					<xsd:element name = "zip" type =
> "xsd:positiveInteger"/>
> 				</xsd:all>
> 			</xsd:extension>
> 		</xsd:complexContent>
> 	</xsd:complexType>
> 
> This schema can't pass the validation check, and the error is "groups are
> not allowed in ALL element".

> But if I change the <all> defined in the base complex type to <sequence>, it
> passed the validation check without any error. Could anybody please explain
> this?

See previous threads.  Extension _always_  results in a top-level
<sequence>, but <all> may not be nested.  So use <sequence>, as I said
above.

> If I define "MyAddress" as a sub-class of "USAddress", can I write the
> schema like the following? I changed <all> of base class to <sequence> and
> defined "MyAddress" as a child of "USAddress".
> 
> 	<xsd:element name = "Address" type = "Address" abstract = "true"/>
> 	<xsd:complexType name = "Address" abstract = "true">
> 		<xsd:sequence>
> 			<xsd:element name = "name" type = "xsd:string"/>
> 			<xsd:element name = "street" type = "xsd:string"/>
> 			<xsd:element name = "city" type = "xsd:string"/>
> 		</xsd:sequence>
> 	</xsd:complexType>
> 	<xsd:element name = "USAddress" type = "USAddress" substitutionGroup
> = "Address"/>
> 	<xsd:complexType name = "USAddress">
> 		<xsd:complexContent>
> 			<xsd:extension base = "Address">
> 				<xsd:all>
> 					<xsd:element name = "state" type =
> "xsd:string"/>
> 					<xsd:element name = "zip" type =
> "xsd:positiveInteger"/>
> 				</xsd:all>
> 			</xsd:extension>
> 		</xsd:complexContent>
> 	</xsd:complexType>
> 	<xsd:element name = "MyAddress" type = "MyAddress"/>
> 	<xsd:complexType name = "MyAddress">
> 		<xsd:complexContent>
> 			<xsd:extension base = "USAddress">
> 				<xsd:all>
> 					<xsd:element name = "Mystate" type =
> "xsd:string"/>
> 					<xsd:element name = "Myzip" type =
> "xsd:positiveInteger"/>
> 				</xsd:all>
> 			</xsd:extension>
> 		</xsd:complexContent>
> 	</xsd:complexType>

No -- still you end up with a nested <all>, not allowed -- use <sequence>.

ht
-- 
  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
          W3C Fellow 1999--2001, part-time member of W3C Team
     2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
	    Fax: (44) 131 650-4587, e-mail: ht@cogsci.ed.ac.uk
		     URL: http://www.ltg.ed.ac.uk/~ht/
Received on Tuesday, 15 January 2002 04:34:29 GMT

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