Operating system abstraction has several benefits. What are the most significant ones?

Shouldn't this part be devoted to describing the two characteristics of an operating system that are considered to be the most important?

Using the output shown in Figure P7.12 as your guide, generate a list of customer purchases, including the subtotals for each of the invoice line numbers. The subtotal is a derived attribute calculated by multiplying LINE_UNITS by LINE_PRICE. Sort the output by customer code, invoice number, and product description. Be certain to use the column aliases as shown in the figure.  In the SQL Query do the following  Select clause: CUS_CODE, INV_NUMBER, P_DESCRIPT, LINE_UNITS AS “Units  Bought”, LINE_PRICE as “Unit Price”, derived attribute Subtotal using the formula  stated above  From: Join conditions between these tables INVOICE, LINE, PRODUCT  Where clause: You can put join conditions here as well if you do not want to put them in the from clause. There are many ways to write the query.  Order by clause: use the columns as stated in the problem description.

In this section, we summarize the two most crucial aspects of an operating system's overall design.