XSD substitution groups, subtypes, nillable .. the whole smack

[Soren Kuula <dongfang@dongfang.dk>]

Hi, I'm trying to make a simpler structure for XML Schema -- by making 
implicit stuff explicit.

If I have three types: a > b > c, meaning c is derived by extension from 
b, b is derived by extension from a

--- scenario 1 ---

For a declaration:

   element x of type a

I take that to mean:

There are three declaration of an element named x:

There is a declared element with name x, type a, and an optional 
attribute xsi:type with value "a" and an optional attribute xsi:nil with 
value space {false}

There is a declared element with name x, with type b, and a requered 
attribute xsi:type with value "b" and an optional attribute xsi:nil with 
value space {false}

There is a declared element with name x, with type c, and a required 
attribute xsi:type with value "c" and an optional attribute xsi:nil with 
value space {false}


Any big conceptual mistakes there? Hope not :)

Now if I add

   element y of type b

that will then be

There exist two declaration of an element named y:

One with type b, and a requered attribute xsi:type with value "b" and an 
optional attribute xsi:nil="false"
One with type c, and a required attribute xsi:type with value "c" and an 
optional attribute xsi:nil="false"

right?

--- scenario 2 ---

If I do

   element x of type a subsitutionGroup="y"

   element y of type b

(with the same implications for implied declarations as above)

can the (first) implied-declaration

There exists a declared element named x with type a, and an optional 
attribute xsi:type with value "a" and an optional attribute xsi:nil="false"

ever substitute a y element? As far as I understand no, but I'd be happy 
to have a confirmation.

--- scenario 3 ---

I take a declaration

   element y of type b nillable="false"

to mean

There exists a declared element named y with type b, and an optional 
attribute xsi:type with values{b} and an optional attribute xsi:nil with 
   values{false}

and

   element y of type b nillable="true"

to mean

There exists a declared element named y with type b, and an optional 
attribute xsi:type with value space {b}, and an optional attribute named 
xsi:nil with value space {false}

There exists a declared element named y with type #EMPTY, and an 
optional attribute xsi:type with value space {b}, and a required 
attribute named xsi:nil with value space {true}

i) How are the other implied declarations; are there 1 or 2 of them? One 
of these must be true:

(R)
There exists a declared element named y with type c, and a required 
attribute xsi:type with value space {c}, and an optional attribute named 
xsi:nil with value space {false}

OR

(S)
(
There exists a declared element named y with type c, and a required 
attribute xsi:type with value space {c}, and an optional attribute named 
xsi:nil with value space {false}

and

There exists a declared element named y with type #EMPTY, and a required 
attribute xsi:type with value space {c}, and an required attribute named 
xsi:nil with value space {true}
)

Which one is it ? :)

--- Scenario 4 ---

if I have

   element x of type b nillable="true" substitutionGroup = "y"

   element y of type b nillable="false"

is is true or false, or absurd to even talk about that elements of the 
implicit declaration

There exists a declared element named x with type #EMPTY, and an 
optional attribute xsi:type with value space {b}, and a required 
attribute named xsi:nil with value space {true}

can substitute elements declared by

There exists a declared element named y with type b, and an optional 
attribute xsi:type with value space {b}, and an optional attribute named 
xsi:nil with value space {false}

(I sure as XML Schema hope it's false)

--- Scenario 5, final one ---

if I have

   element x of type b nillable="true" substitutionGroup = "y"

   element y of type b nillable="true"

is is true or false that elements of the implicit declaration

There exists a declared element named x with type #EMPTY, and an 
optional attribute xsi:type with value space {b}, and a required 
attribute named xsi:nil with value space {true}

can substitute elements declared by

There exists a declared element named y with type #EMPTY, and an 
optional attribute xsi:type with value space {b}, and a required 
attribute named xsi:nil with value space {true}

my bold guess is that it's true, but maybe....



All right, I could go looking for the answers in the spec, but honestly, 
I don't have the courage for that; I'm still in R&R after my last 
encounter with it. My hope with this is that someone really 
knowledgeable about XML Schema can fill me / us in on it, and together 
we have then contributed a really simple way to tell how the whole 
subtyping / subst grp / nillable thing works.

Soren