Sara,
Here is some guidance on one way you can look at how to define your portfolio. This view aligns your portfolios to lines of business or business services in order to get visibility into "Total Cost of Ownership" and how that compares to the revenue of your line of business, product, or service.
Good portfolio management should help executives answer whether a line of business, product, or service, is profitable and where to invest and divest. This will align to the company's mission and goals. Budgets will then be allocated based on this answer to fund programs and projects within a portfolio. Sometimes an entire portfolio goes way if it is not profitable enough
Unfortunately PMI does not go far enough....
Below is an updated view that takes into consideration operational assets and other non project investments.
Hope that helps. I facilitate guidance/advisory workshops in the PPM space to help companies define their PPM practices.
