Re: Use-case for a complex type that has no valid content?

From: Michael Kay <mike@saxonica.com>
To: "Costello, Roger L." <costello@mitre.org>
Date: Tue, 2 Jun 2015 20:47:33 +0100

Play the video

The main use of a void type is that it helps you construct a system with closure properties, so you can have operators on types (e.g. the intersection of two types) where the result of the operation is always a legitimate type.

Use-cases are the bane of orthogonality. Any system with good orthogonality can do things for which it is very difficult to find a use case. What’s the use case for adding two negative numbers? Design focused excessively on use-cases leads to a lack of orthogonality.

XSD 1.1 introduced xs:error which is a void simple type. It’s defined similarly to <xs:choice/> as a union with no member types. The specific use case for introducing it was for conditional type assignment, it allows you to have the last alternative in a list of alternatives say “if none of the above conditions is true, then the type is xs:error, meaning no content is accepted”.

Michael Kay

Saxonica

On 2 Jun 2015, at 18:44, Costello, Roger L. <costello@mitre.org> wrote:

Hi Folks,

Thanks for the outstanding responses.

I have learned that an empty choice:

    <xs:complexType name="ValidationKiller">
        <xs:choice/>
    </xs:complexType>

has no valid content, i.e., the set of valid content is the empty set, {}.

When would one use such a complex type? Can you think of a use-case for it?

/Roger

References:
- Use-case for a complex type that has no valid content?
  - From: "Costello, Roger L." <costello@mitre.org>

[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index]

PURCHASE STYLUS STUDIO ONLINE TODAY!

Purchasing Stylus Studio from our online shop is Easy, Secure and Value Priced!

Download The World's Best XML IDE!

Accelerate XML development with our award-winning XML IDE - Download a free trial today!

Subscribe in XML format

RSS 2.0
Atom 0.3

Stylus Studio has published XML-DEV in RSS and ATOM formats, enabling users to easily subcribe to the list from their preferred news reader application.

Stylus Studio Sponsored Links are added links designed to provide related and additional information to the visitors of this website. they were not included by the author in the initial post. To view the content without the Sponsor Links please click here.

XML Editor - Download a 15 Day Free Trial Now >

See What's New in Stylus Studio >

Buy Stylus Studio - XML Editor - Now >