Step 1: Arrange the data in ascending order

Sort the given data set from smallest to largest: 12, 21, 23, 34, 44, 45, 56, 67, 89.

$12, 21, 23, 34, 44, 45, 56, 67, 89$

Step 2: Count the total number of observations

Count the total number of terms in the dataset, which gives $n = 9$. Since 9 is an odd number, we use the median position formula for odd $n$.

$n = 9$

Step 3: Apply the median position formula

Substitute $n = 9$ into the formula to find the position of the median term: $\frac{9 + 1}{2} = 5\text{-th term}$.

$5\text{-th term}$

Step 4: Identify the median value

Locate the 5th term in the sorted sequence, which is $44$.

$\text{Median} = 44$