An enterprise-level application does not require a case type ruleset.

An enterprise application's access group's work pool can be set to "PegaSample".

its actually mentioned in the architecture course.. Not sure why..

There's not much detail about what exactly they meant by enterprise case type ruleset.. 

in page no 120 in LSA guide its given as below:

"This is a different ruleset from the enterprise application’s case type ruleset."

There are two ways to create an enterprise application:, the first being using the New Application Wizard. Four rulesets will be added to the application, two org-level and two application-level.

The second is saving an existing application to a new ruleset, removing the application-level / work pool / integration rulesets from that application, removing the org-level rulesets from the original application, making the original application built on the new org-level application.

Using the second approach you need to specify a work pool to be able to use the App Explorer in Dev Studio. The PegaSample class would suffice but not as useful as having a Org-specific set of examples.

Since the Org class extends Work-Cover you could modify its Class rule to say that it "is a class group" then define a corresponding Data-Admin-DB-ClassGroup record mirroring what the PegaSample class does.

It would be better, though, to use an OrgSample class for examples, those examples defined in a ruleset other than the Org ruleset. This brings you back to the first approach. Start there creating an OrgSample application then use the second approach to place the Org-level rulesets in a separate Org-level application on which other applications are built.