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RE: Style, Substance and Typing in Schemas

  • From: "David Lee" <dlee@calldei.com>
  • To: "'Michael Kay'" <mike@saxonica.com>, <xml-dev@l...>
  • Date: Wed, 12 Oct 2011 06:21:13 -0400

RE:  Style

With absolutely NO knowledge whatsoever, I will take a poke in the dark.

 

Since in Java,  URI is not a subclass of String,  it make sense that anyURI in XSD should not be a subclass of String.

 

More abstractly, I could see the argument that anyURI by nearly coincidence is a string representation of a URI but really is its own structured type  (protocol + host + file part + query ... )  similar as one might say  a Point object could have a String representation "X,Y" but that doesn't make it a subclass of String, or even integer could be but isn't a subclass of string.

 

-David

 

 

----------------------------------------

David A. Lee

dlee@calldei.com

http://www.xmlsh.org

 

From: Michael Kay [mailto:mike@s...]
Sent: Wednesday, October 12, 2011 5:40 AM
To: xml-dev@l...
Subject: Re: Style, Substance and Typing in Schemas

 

If you're only using a schema for validation, then the type hierarchy makes very little difference (except perhaps for some maintainability benefits if you get it right - but even then, not much).

If you're using the schema to define types that are then used for processing, then the details of what works well may depend on your processing environment - for example optimizing the schema for processing in schema-aware XSLT and XQuery may not be the same as optimizing for JAXB (union types, for example, might or might not be well supported). However, in all cases, getting the type hierarchy to match the conceptual object model in the real world is a good aim. This requires judgement; the designers of XSD decided, for example, that anyURI was not a subtype of string, and they have never been able to give me a convincing reason why, but it was based on some kind of subjective analysis of the real-world semantics.

Michael Kay
Saxonica

On 11/10/2011 15:29, Toby Considine wrote:

I have a question of Style and Substance in XSD

 

I have a number of top-level elements that are variants of one another. Each of these appears in multiple Types (worthy of top-lelvelness).

 

Let’s say we have uid as a simple base type.

 

<xs:element name="uid" type="UidType"/>

<xs:simpleType name="UidType">

                <xs:annotation>

                                <xs:documentation>Unique Identifier</xs:documentation>

                </xs:annotation>

                <xs:restriction base="xs:string"/>

</xs:simpleType>

 

A)           One approach has me fully typing each derived element

 

<xs:element name="fooID" type="FooType"/>

<xs:simpleType name="FooType">

                <xs:annotation>

                                <xs:documentation>Identification of foo. </xs:documentation>

                </xs:annotation>

                <xs:restriction base="UidType"/>

</xs:simpleType>

<xs:element name="feeID" type="FeeIDType"/>

<xs:simpleType name="FeeIDType">

                <xs:annotation>

                                <xs:documentation>Identification of fee </xs:documentation>

                </xs:annotation>

                <xs:restriction base="UidType"/>

</xs:simpleType>

<xs:element name="fieID" type="FieIDType"/>

<xs:simpleType name="FieIDType">

                <xs:annotation>

                                <xs:documentation>Identification of fie </xs:documentation>

                </xs:annotation>

                <xs:restriction base="UidType"/>

</xs:simpleType>

<xs:element name="fumID" type="FumIDType"/>

<xs:simpleType name="FumIDType">

                <xs:annotation>

                                <xs:documentation>Identification of Fum </xs:documentation>

                </xs:annotation>

                <xs:restriction base="UidType"/>

</xs:simpleType>

 

B)            The other approach has me simply declaring each element.

 

<xs:element name="fooID" type="UidType">

                <xs:annotation>

                                <xs:documentation>Identification of foo. </xs:documentation>

                </xs:annotation>

</xs:element>

<xs:element name="feeID" type="UidType">

                <xs:annotation>

                                <xs:documentation>Identification of fee </xs:documentation>

                </xs:annotation>

</xs:element>

<xs:element name="fieID" type="UidType">

                <xs:annotation>

                                <xs:documentation>Identification of fie </xs:documentation>

                </xs:annotation>

</xs:element>

<xs:element name="fumID" "UidType">

                <xs:annotation>

                                <xs:documentation>Identification of Fum </xs:documentation>

                </xs:annotation>

</xs:element>

 

Question: Why would I choose (A) or (B)?

 

SO far, I can find that in many code bases, in the first, I can’t say

 

this.FooID = that.FeeID

 

but must instead say something like

 

this.FooID = cast(that.FeeID ).to FooIDType

(varies on language, implementation, of course)

 

This may be god if a FooId should never be a FeeId but may be bad in other cicumstances.

 

Is this more than a style concern?Are there deeper concerns I am overlooking?

 

Thanks

 

tc

 


“The single biggest problem in communication is the illusion that it has taken place.”
– George Bernard Shaw.


Toby Considine
TC9, Inc

TC Chair: oBIX & WS-Calendar

TC Editor: EMIX, EnergyInterop

U.S. National Inst. of Standards and Tech. Smart Grid Architecture Committee


  

Email: Toby.Considine@g...
Phone: (919)619-2104

http://www.tcnine.com/
blog: http://www.NewDaedalus.com

 

 

 



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