RE: [xml-dev] Conditional xml Schema

[Winchel 'Todd' Vincent III <winchel@mindspring.com>]

Erik:

 

Thanks for the kind reply.

 

Todd

-----Original Message-----
From: Erik Wright
Sent: Jun 13, 2006 9:32 AM
To: Winchel 'Todd' Vincent III , schaffner.joe@gmail.com
Cc: xml-dev@lists.xml.org
Subject: RE: [xml-dev] Conditional xml Schema

Hi Todd,

 

I totally agree. In our schemas we do not use a "Type" suffix. But for people who aren't familiar with XSD (and the fact that type and element namespaces are distinct) I wanted to artificially distinguish the two namespaces.

 

Cheers,

 

Erik

---

From: Winchel 'Todd' Vincent III [mailto:winchel@mindspring.com]
Sent: June 12, 2006 6:53 PM
To: Erik Wright; schaffner.joe@gmail.com
Cc: xml-dev@lists.xml.org
Subject: Re: [xml-dev] [Summary] Media type (MIME) of XML in MS Word? in Notepad? when compressed? etc

Erik:

Just a small point about Orange and OrangeType . . . since this person is new to XML Schema, it should be pointed out that using the string "Type" is unnecessary, redundant, and bloats schemas.

<xsd:element name="Thing" type="Thing">

<xsd:element name="Thing" type="ThingType">

You can also do this:

<xsd:element name="Fruit" type="Orange">

Which is no differen than this . . .

<xsd:element name="Fruit" type="OrangeType">

. . . it is just less text and results in a smaller schema.

In XML Schema, since the name attribute signals the name of the element and the type attribute the type, it is not neceesary to include the extra string "Type" on the end of the type attribute value. It just adds extra text. This extra text gets in the way of writing XSLT, code, etc. when ever you want to process the XML Schema as XML.

There is no difference, from an XML Schema perspective, between the above constructs, so you do not gain or loose anything from an XML Schema perspective. From a text perspective, you save a number of characters. I once eliminated the Type strings from an unusually large XML schema and saved 42 KB without changing a thing. 42 KB can have a real impact on performance, depending on your environment.

Thanks,

Todd

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-----Original Message-----

From: Erik Wright [mailto:erik.wright@radialpoint.com]

Sent: Monday, June 12, 2006 6:15 PM

To: Joe Schaffner

Cc: Ramkumar Menon; Jirka Kosek; Jagdishwar B; xml-dev@lists.xml.org

Subject: RE: [xml-dev] Conditional xml Schema

In the case of <choice/>, you will specify a choice of either an element named "Orange" of type "OrangeType", or an element named "Apple" of "AppleType".

An instance document will have one or the other (or multiple elements, each of which is either Apple or Orange, if you use minOccurs+maxOccurs).

Schema validation is easy in this case. If the element is named Apple, the AppleType schema rules apply. If it is named Orange, the OrangeType rules apply.

In the case of using polymorphism, you will define an element named "Fruit" of type "FruitType". So how does the document consumer know if it is an instance of AppleType or OrangeType? You must specify the type in the XML instance document:

<Fruit xsi:type="AppleType">

...

</Fruit>

Regarding your "Where does XML run" question... An application that consumes XML documents MAY validate the documents using a schema. In that case, the application must get the XML instance document, get the XML schema document, and invoke a schema validation engine that compares the instance to the schema.

In Java, for example, you can create an XMLParser, enable the XSD schema validation option, and when you load any document that specifies an xml schema (using the optional xsi:schemaLocation attribute) the schema will automatically be retrieved to validate the doc. Parsing will fail if the validation fails. In the most recent version of the Java XML APIs there is a direct way to construct a validator from a schema. You can then pass as many documents as you want (with no custom markup) through the validator.

Another way XSD is used is in defining web service contracts (as part of a web service desctription, or WSDL, file). In the simplest case, the XSD may be used by your web service engine to automatically build a Java/C++ object model that maps to the XSD objects used by your service. When a SOAP request is received, it is validated against the XSD and then automatically deserialized into the Java/C++ objects, which are then given to your web service implementation. When your service implementation returns its results (as objects) the web service engine will convert them back into XML that matches the XSD and return that to the client in a SOAP response.

-Erik

> -----Original Message-----

> From: Joe Schaffner [mailto:schaffner.joe@gmail.com]

> Sent: June 12, 2006 3:07 PM

> To: Erik Wright

> Cc: Ramkumar Menon; Jirka Kosek; Jagdishwar B; xml-dev@lists.xml.org

> Subject: Re: [xml-dev] Conditional xml Schema

>

> Thanks Erik,

>

> Yours looks like the canonical approach, like C++ classes, or

> C unions, but I'll have to get used to idea of cross-field validation.

> It sounds strange to me. Just a quick glance online seemed to

> indicate this was some sort of field validation, where you

> want to be sure that elememt content comes from some

> well-defined domain.

>

> Since I am not familiar with the procedural semantics of XML,

> I do not know how someone would validate user-defined types.

> It looks like XML can contain procedures written in Java, but

> now I'm getting confused by the operating environments. Just

> where does the XML run?

>

> Joe

> http://modern-greek-verbs.tripod.com/agv/

>

> On 6/12/06, Erik Wright <erik.wright@radialpoint.com> wrote:

> > XSD supports this type of behaviour in various ways.

> >

> > One way is to define a base type (fruit) and extend it with

> other types (apple, orange). Then when defining the container

> element, you would define it as having children of type

> fruit. The instance document could incorporate either type.

> >

> > Another way is to use the choice element in your schema. It

> matches one of a specific list of types. To have several

> fruit (each of which might be apple or orange) you can use

> the minOccurs and maxOccurs attributes on the choice.

> >

> > -Erik

> >

> > > -----Original Message-----

> > > From: Ramkumar Menon [mailto:ramkumar.menon@gmail.com]

> > > Sent: June 11, 2006 2:10 PM

> > > To: Joe Schaffner

> > > Cc: Jirka Kosek; Jagdishwar B; xml-dev@lists.xml.org

> > > Subject: Re: [xml-dev] Conditional xml Schema

> > >

> > > Cross field constraints are better off described thru rule based

> > > validation languages like schematron. Use this in

> conjunction with

> > > the XSD to enable cross field validation on fields.

> > >

> > > <pattern name="checkMangoOrApple">

> > > <rule context="Fruit">

> > > <assert test="@myAttr='Apple' and elementApple1>If myAttr is

> > > apple, elementApple1 should be present"/>

> > > <assert test="@myAttr='Mango' and elementMango1>If myAttr is

> > > mango, elementMango1 should be present"/>

> > > </rule>

> > > </pattern>

> > >

> > >

> > >

> > > On 6/11/06, Joe Schaffner <schaffner.joe@gmail.com> wrote:

> > > > Why don't you define a Mango element and an Apple element,

> > > each with

> > > > their own structure? I'll bet there is even a way to define a

> > > > Fruit element, then derive an Apple and a Mango from Fruit. Then

> > > you would

> > > > instantiate either type of fruit, Apple or Mango, and get

> > > the proper

> > > > structure.

> > > > Joe

> > > > http://modern-greek-verbs.tripod.com/agv/

> > > > PS

> > > > It looks like you are trying to use the attribute to name

> > > the element

> > > > type, which would be unnecessary, and it would surprise me

> > > if xsd --

> > > > or any schema definition language -- would attribute class

> > > semantics

> > > > to the arrtibutes you create arbitrarily. You are trying to

> > > place your

> > > > metadata in the data domain.

> > > >

> > > > On 6/11/06, Jirka Kosek <jirka@kosek.cz> wrote:

> > > > > Jagdishwar B wrote:

> > > > >

> > > > > > Is it possible to define the xml schema (xsd)

> > > conditionally based

> > > > > > on certain values.

> > > > >

> > > > > No. You have to use RELAX NG or Schematron to express

> > > such constraints.

> > > > >

> > > > > --

> > > > >

> ------------------------------------------------------------------

> > > > > Jirka Kosek e-mail: jirka@kosek.cz

> http://www.kosek.cz

> > > > >

> ------------------------------------------------------------------

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> > > > >

> ------------------------------------------------------------------

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> ----------------------------------------------------------------

> > > > > --

> > > > >

> > > > >

> > > > >

> > > > >

> > > >

> > >

> > >

> > > --

> > > Shift to the left, shift to the right!

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> > >

> > > -Ramkumar Menon

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> > >

> > >

> >

>

>

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