In a conference, five participants are seated in a row: Alan, Bob, Chris, David and Edward. Alan is not next to Chris. Bob is seated between Alan and David. Alan sits on one end. David is not next to Edward. Who is seated in the middle?

Let's construct the arrangement coordinates from 1 to 5:
1. Alan sits on an end. Let's position Alan at index 1.
2. Bob sits between Alan and David $⟹$ Position 2 = Bob, Position 3 = David. This yields:

$$\text{Alan}\to \text{Bob}\to \text{David}$$

3. "David is not next to Edward" means Edward cannot be placed at Position 4. Therefore, Edward must take Position 5.
4. The remaining Position 4 goes to Chris.

The final sequence is:

$$\text{Alan (1)}-\text{Bob (2)}-\text{David (3)}-\text{Chris (4)}-\text{Edward (5)}$$

David sits at the middle position (3).