Animal-friends implemented as a pattern (Re: XML-Data: advantages over DTD syntax?)

[Rick Jelliffe]

> From: Jonathan Robie <jwrobie at mindspring.com>
 
> <xml:schema>
>   <elementType id="animalFriends">
>     <elt href="#pet" occurs="PLUS"/>
>   </elementType>
> 
>   <elementType id="pet">
>     <any/>
>     <attribute id='name'/>
>     <attribute id='owner'/>
>   </elementType>
> 
>   <elementType id="cat" extends="#pet"/>
>     <elt href='#kittens'/>
>     <attribute id='lives' type='NMTOKEN'/>
>   </elementType>
> 
>   <elementType id="dog" extends="#pet"/>
>     <elt href='#puppies'/>
>     <attribute id='breed'/>
>   </elementType>
> <xml:schema>
> 
> Now I can use this type declaration to create an animalFriends element,
> which is a list of pets:
> 
> <animalFriends>
>   <cat name="Fluffy" lives='9'/>
>   <pet name="Diego"/>
>   <dog name="Gromit" owner='Wallace' breed='mutt'/>
> </animalFriends>
> 
> So the pet hrefs can point to pets, cats, or dogs.
> 
> How would I create this schema using architectural forms?

And you do not even need architectural forms. Here is a very
simple pattern for doing everything your example does using
a single DTD and standard SGML! (The suffixes "-content"
and "-attributes" are reserved for use in patterns. The
attribute "is-a" is reserved to allow inheritence labelling.)

<!DOCTYPE animal-friends
[

<!-- Handle animal friends ================================= -->
<!ENTITY % animal-friends-content 
	" ( pet | cat | dog )+")
<!ENTITY % animal-friends-attributes
	" ">
<!ELEMENT  animal-friends
	( %animal-friends-content; )>
	<!ATTLIST animal-friends
		%animal-friends-attributes;
	>

<!-- Handle pets =========================================== -->
<!ENTITY % pet-content 
	"ANY" >
<!ENTITY % pet-attributes 
	" name ID #IMPLIED
	owner ID #IMPLIED 
	is-a CDATA #FIXED 'pet' " >  <!-- does not handle multiple inheritance! -->
<!ELEMENT pet
	( %pet-content; ) >
	<!ATTLIST pet
		%pet-attributes;
	>

<!-- Handle cats =========================================== -->
<!ENTITY % cat-contents
	( " (kittens)? " )
<!ENTITY % cat-attributes
	" lives NMTOKEN #IMPLIED ">
<!ELEMENT cat
	( %pet-content;, %cat-contents; )
 	<!ATTLIST cat
		%pet-attributes;
		%cat-attributes;
	>

<!-- Handle dogs =========================================== -->
<!ENTITY % dog-contents
	( " (puppies)? " )
<!ENTITY % dog-attributes
	" breed CDATA #IMPLIED ">
<!ELEMENT dog
	( %pet-content;, %dog-contents; )
 	<!ATTLIST dog
		%pet-attributes;
		%dog-attributes;
	>
]>

<animalFriends>
  <cat name="Fluffy" lives='9'/>
  <pet name="Diego"/>
  <dog name="Gromit" owner='Wallace' breed='mutt'/>
</animalFriends>


If you want multiple inhereitance, then you can just 
define a different suffix, and search through attributes
based on that to collect the inheritance tree. I can
provide an example if anyone is interested.

Anyone who is aware of the pattern can see this and implement
it just as easily as they could using XML-data's syntax,
but without breaking SGML compatibility, which generating
new element types outside declarations does.

Rick Jelliffe

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