Deploying SharePoint 2007 Custom Content Types using Inheritance with a SharePoint Feature

I had the following question sent to me this morning regarding the creation of custom content types:

"I need to create custom content types in MOSS 2007 and want to know the best way to do it. I want to achive the inheritance such as: My Core Content Type --- > Generic Content Type -- > News Content Type"

You will find that Microsoft themselves use a feature as the mechanism to deploy all of the out of the box (OOB) content types. You can see this file at:
"C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\12\TEMPLATE\FEATURES\ctypes\ctypeswss.xml".

In fact, the feature.xml file that Microsoft uses is in the same directory. This uses a standard schema, which can be found on MSDN here http://msdn.microsoft.com/en-us/library/ms463449.aspx

Which brings me to the content type inheritance part of the question.

The critical part to understand when creating the feature is that inheritance in content types is defined by the Ctype ID. If you go to the Content Type Gallery (for your site/site collection) and create a new content type, you can see this ctype in the URL when you hover over the name of your new content type in the gallery list. For example, when I click on the content type I just created, the link was to this location:
http://servername/_layouts/ManageContentType.aspx?ctype=0x0100E00AAE6F9A33274BBC67EACB89D61FFA&Source=%2F%5Flayouts%2Fmngctype%2Easpx

When I create a new content type that inherits from the other content type, then I just append a 01 to it and it inherits from the parent type. i.e. the Content Type Id is
ctype=0x0100E00AAE6F9A33274BBC67EACB89D61FFA01
A "grandchild" of the parent type would be
ctype=0x0100E00AAE6F9A33274BBC67EACB89D61FFA0101
and so on.

In summary, to answer the question:

1. Create a feature to deploy your content types (using WSPBuilder or your preferred tool).
2. In the elements file, specify your content type id (ctype) and fields which should be displayed.
3. Give the wsp file to SharePoint administrators to Deploy the file.
4. Done!

Additional Notes/References

1. Another option which allows more control and full programmatic flexibility would be to create a feature receiver which then allows you to run code against the SharePoint object model to perform additional checks in the OnFeatureActivated/OnFeatureInstalled event
2. As a best practice, Content types should not be modified by a feature once they have been installed - as manual changes to the content type may be overwritten.
3. One of the most illuminating articles on this topic can be found here:
   http://blogs.msdn.com/eigilm/archive/2007/09/04/inherit-content-types.aspx