- From: Andy Davidson <andy_davidson@apple.com>
- Date: Thu, 10 Mar 2011 11:07:55 -0800
- To: "Costello, Roger L." <costello@mitre.org>
- Cc: "xmlschema-dev@w3.org" <xmlschema-dev@w3.org>
Just my 2 cents I work on a very large project with over 100 engineers building clients and services using Java and ObjC. Most of these engineers are fairly inexperience and are not experts on xml schema. <choice> is very easy for them to understand, "ref" causes lots of confusion and bugs. We use choice in our request/response definitions. The response is either a "result" or an "error". Switching our interfaces to work this way has dramatically reduced the number of bugs in our system Please do not remove <choice> I am not sure how well it is supported in JAXB/XJC. We do not have any support of "ref" in ObjC code generators. Does libxml run time validate refs correctly? Andy On Mar 8, 2011, at 6:36 AM, Costello, Roger L. wrote: > Hi Folks, > > Here is an example of using xsd:choice. The content of <transportation> is a choice of either <train>, <plane>, or <automobile>. > > <xsd:element name="transportation"> > <xsd:complexType> > <xsd:choice> > <xsd:element name="train" type="xsd:string"/> > <xsd:element name="plane" type="xsd:string"/> > <xsd:element name="automobile" type="xsd:string"/> > </xsd:choice> > </xsd:complexType> > </xsd:element> > > Rather than using xsd:choice, the schema could be designed using xsd:sequence. The sequence consists of an element that ref's to an abstract mode-of-transportation element. The train, plane, and automobile elements are globally declared and are substitutable with mode-of-transportation. > > <xsd:element name="transportation"> > <xsd:complexType> > <xsd:sequence> > <xsd:element ref="mode-of-transportation" /> > </xsd:sequence> > </xsd:complexType> > </xsd:element> > > <xsd:element name="mode-of-transportation" abstract="true" type="xsd:string" /> > > <xsd:element name="train" substitutionGroup="mode-of-transportation"/> > <xsd:element name="plane" substitutionGroup="mode-of-transportation"/> > <xsd:element name="automobile" substitutionGroup="mode-of-transportation"/> > > I believe that the two designs produce identical results. > > Suppose the xsd:choice element were jettisoned from the XML Schema specification. Would there be any loss of functionality? Put another way, can you provide a real-world, compelling example of a schema that uses xsd:choice which cannot be expressed using abstract element plus substitution groups? > > /Roger >
Received on Thursday, 10 March 2011 19:08:29 UTC