What are best practices for designing XML schemas? [closed]

Question

As an amateur software developer (I'm still in academia) I've written a few schemas for XML documents. I routinely run into design flubs that cause ugly-looking XML documents because I'm not entirely certain what the semantics of XML exactly are.

My assumptions:

<property> value </property> 

property = value

<property attribute="attval"> value </property> 

A property with a special descriptor, the attribute.

<parent>   <child> value </child> </parent> 

The parent has a characteristic "child" which has the value "value."

<tag /> 

"Tag" is a flag or it directly translates to text. I'm not sure on this one.

<parent>   <child /> </parent> 

"child" describes "parent." "child" is a flag or boolean. I'm not sure on this one, either.

Ambiguity arises if you want to do something like representing cartesian coordinates:

<coordinate x="0" y="1" />  <coordinate> 0,1 </coordinate>  <coordinate> <x> 0 </x> <y> 1 </y> </coordinate> 

Which one of these options is most correct? I would lean towards the third based upon my current conception of XML schema design, but I really don't know.

What are some resources that succinctly describe how to effectively design xml schemas?

Answer 1

One general (but important!) recommendation is never to store multiple logical pieces of data in a single node (be it a text node or an attribute node). Otherwise, you end up needing your own parsing logic on top of the XML parsing logic you normally get for free from your framework.

So in your coordinate example, <coordinate x="0" y="1" /> and <coordinate> <x>0</x> <y>1</y> </coordinate> are both reasonable to me.

But <coordinate> 0,1 </coordinate> isn’t very good, because it’s storing two logical pieces of data (the X-coordinate and the Y-coordinate) in a single XML node—forcing the consumer to parse the data outside of their XML parser. And while splitting a string by a comma is pretty simple, there are still some ambiguities like what happens if there's an extra comma at the end.

Answer 2

See the tutorial:

• "XML Schemas: Best Practices" by Roger Costello.

I also recommend:

• Priscilla Walmsley's book "Definitive XML Schema".

• Jeni Tennison's XML Schema pages