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Hi Folks,
Here is the next issue that I would like to take up on XML Schema
Best Practices.
Issue: Public versus Private Schemas - When should a schema be made
publicly accessible versus when should it be kept private? Are
there guidelines on what should be in a public schema?
I would like to kick off this discussion with some thoughts
that I have on this topic: I think that as a quick and dirty
general rule types (complexTypes and simpleTypes) should go in
public schemas and global element declarations should go in private
schemas.
Example. Consider these schema components:
<complexType name="PublicationType" abstract="true">
<sequence>
<element name="Title" type="string"/>
<element name="Author" type="string" maxOccurs="unbounded"/>
<element name="Date" type="year"/>
</sequence>
</complexType>
<complexType name="BookType">
<complexContent>
<extension base="c:PublicationType" >
<sequence>
<element name="ISBN" type="string"/>
<element name="Publisher" type="string"/>
</sequence>
</extension>
</complexContent>
</complexType>
<complexType name="MagazineType">
<complexContent>
<restriction base="c:PublicationType">
<sequence>
<element name="Title" type="string"/>
<element name="Author" type="string"
minOccurs="0" maxOccurs="0"/>
<element name="Date" type="year"/>
</sequence>
</restriction>
</complexContent>
</complexType>
<element name="Catalogue">
<complexType>
<sequence>
<element name="Publication" type="c:PublicationType"
minOccurs="0" maxOccurs="unbounded"/>
</sequence>
</complexType>
</element>
There are 3 type definitions - Publication, BookType, and MagazineType.
There is one global element declaration - Catalogue.
As a first pass, I would put the 3 type definitions into a schema and
make that schema publicly accessible. I would put the global element
declaration into a second, private schema.
Here's my reasoning for this method of partitioning schema components
into public versus private schemas:
- Types are by definition reusable components. So, immediately I
think "public".
- Element declarations get instantiated in instance documents. They
are domain specific components, i.e., not general purpose. So,
immediately I think "private".
Okay, those are some of my quick, probably-not-well-thought-out
thoughts on this topic. What are your thoughts? Can you think of a
more refined methodology for partitioning components among public
versus private schemas? What is your decision process for deciding
if a component should be made publicly accessible? What is your
definition of a "Public Schema"? What is your definition of a
"Private Schema"?
My hope is that we can have broader participation in discussing this
issue. These Best Practices are to be a "collective effort", so now
is your chance to voice your thoughts. /Roger
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