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Finally, we allow the user to trade for midnights on their watch list from the watch list page because that is why the watch list page exists.
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Implementation
Describe the internals of your implementation, but keep the discussion on a high level. Discuss There were a few important design decisions you we made in on the implementation . Also discuss how implementation problems may have affected the usability of your interfacelevel.
Design Decision I: Store All Bid/Asks, But Display Only the Best
We mentioned this earlier. Our original design showed all the bids, along with the usernames of the people who posted them. Now, we chose to display only the best. This made our design easier to implement and better from a usability standpoint. The constant content size allowed for the reuse of the table interface that we'd use for the schedule page. Furthermore, the 'click-to-offer' pop-up interface was much simplified by having a fixed-length table. The usability aspect was discussed earlier; the only extra point we'll make is that anonymity is important on a fair market.
Design Decision II: Display Prices in Tables Similar to How Midnights are Displayed
Although we changed the way MidnightExchange ran (mentioned above) to more accurately reflect a stock exchange, we chose to display the information in a more user-friendly manner than the stock exchange (i.e. in the same way the schedule page displayed assigned midnights). Again, this was easier to implement and had positive usability repercussions. For the majority of users, the display bears more resemblance to the real world, and is thus easier to learn.
Design Decision III: No Ajax
We couldn't figure out how to use Ajax in time, so we didn't. Thus, while the page refreshes when the user himself puts a bid on the market, it doesn't refresh when other users put bids on the market. This is a potentially catastrophic usability issue, since using old market data can very easily lead to inconsistent pricing and misinformed decisions. Clearly, there was no incentive for us to avoid Ajax except that we couldn't figure it out.
Design Decision III: Yes, PHP and mySQL
We could figure out how to use PHP and mySQL in time, so we did. This meant that we could maintain user data on-line. This is obviously very important if the interface is actually used in real life, since a midnight exchange whose transactions are ephemeral is useless.
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Evaluation
We conducted a user test on Sunday, May 8th, 2011 at the MIT Student Center.
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