Usually case data is stored in the work tables in PegaData. 

If you want to store the case data in a local data source, you may create the table with all required properties and map the work class database instance to that. It would work, but i havent tried it.

You can use the data in from one case in another case by running a report. 

If you could explain the usecase you are trying to acheive, we can give more inputs. Thanks.

You can use Savable DataPage and a method Save-DataPage to save data which resides outside the case in a data type. Same data can be referred in another case by passing the key as parameter to the datapage,