下图由 9 个完全相同的正方形组成。图中未阴影部分占整个图形的几分之几？

1. Determine the total area of the figure in terms of small squares.

The figure is a $3 \times 3$ grid, so the total area is $9$ squares.

2. Calculate the unshaded area in the top and middle rows.

Top row: The top-left and top-middle squares each have half unshaded ($0.5 + 0.5 = 1$ square). The top-right square is completely unshaded ($1$ square). Total for top row = $2$ squares.
Middle row: The middle-left square has half unshaded ($0.5$ square). The middle-middle square is completely unshaded ($1$ square). The middle-right square is completely shaded ($0$ squares). Total for middle row = $1.5$ squares.

3. Calculate the unshaded area in the bottom row.

Bottom row: The unshaded triangle across the bottom-left and bottom-middle squares has a base of $2$ squares and a height of $1$ square. Its area is $\frac{1}{2} \times 2 \times 1 = 1$ square. The bottom-right square has half unshaded ($0.5$ square). Total for bottom row = $1.5$ squares.

4. Find the total unshaded area and the required fraction.

Total unshaded area = $2 + 1.5 + 1.5 = 5$ squares.
Fraction of the figure not shaded = $\frac{5}{9}$.