Portfolio Plan calss category

Dear Experts,

How to design the for any business the unique class category?

1) Is it unique in nature across Installation like project number or name?

Since this is a classification, we need to maintain a list of class codes which are suitable for Our business.

If we have 4 categories applicable for our business across countries, and Portfolio plan is created one level up Organization (like HUB) than business groups, we will usually have 4 Capex spending categories.

We plan to create one Portfolio plan each year at Hub level (higher org than BG) against One Capex category (say Capital spending code) for 'Portfolio Plan1', then we can not use that 'Capital spending' anymore for next year Portfolio plan.