Opening Bid: One Diamond - 11-16 HCP
This particular bid is probably the most frequent of all when you play a forcing club system; it is also the weak point of the bidding structure, because it gives the responder almost no information other than the fact that her partner has an opening hand. It can be as short as a singleton. The point count is 11-16 HCP and should be alerted as, "May be short."
Four Diamonds and Five Clubs
The opening bid is 1 when opener has both a 4-card diamond suit and also a 5-card club suit. There's a bridge term that describes the auction where the second suit is longer than the first... It's a Canapé bid. All Big Club systems use this treatment.
Five Card Diamond Suit
Because an opening call of 2 shows a hand with a 5-card diamond suit and no 4-card major, the 1 bid denies that holding. If the opening bid is 1 and opener later rebids the suit, she must also have an unspecified 4-card major that prevented her from opening 2. (Responder will not usually know about the 4-card major until opener's second call.)
Treat your partner's 1 as semi-forcing. You can pass with a weak hand, but only if you have at least four diamonds. If you don't have that many, even with zero points, find a bid. It's not going to be much fun for your partner to play in a 2-2 fit when she is looking at a zero-point dummy.
In general, if you have at least 7 points or more, the bidding will go rather normally. Bid the way you have always responded to a minor suit opening by naming a biddable major. What we need to discuss, though, are those very weak hands that are short in diamonds.
Consider this hand... (And hope you never see it at the table.)
At first glance, after learning that you should not pass with this garbage, you probably are thinking, "Okay, I guess I will bid 1." Nope. Don't even consider it! Your response is 1 which your partner will alert and then tell the opponents that you might have a 3-card heart suit.
If your partner has a 4-card spade suit she will bid it and you can pass with a sigh of relief. Hey, you are only at the one level. The worst that will happen is that she might raise you to two hearts, but the 4-3 fit in hearts will probably be a better contract than diamonds. Another thing... you should not play support doubles for hearts, but it's okay for spades.
One Notrump Response
And, if the hand above did not have that 4-card spade suit, you should not consider bidding 1NT, either. Weak hands are better played in a suit. Make the agreement with your partner that a 1NT response to her opening bid of 1 shows 9-11 HCP.
Responder's Jump Shift
Most players today play that a Jump Shift by responder is a weak bid, but many expert level players are giving up on this treatment, and many are now using Soloway Jump Shifts showing a hand with at least 16 points. Unfortunately, we don't get that sort of hand as often as we get 6-card suits with 8-10 points.
A Jump Raise, but only in the diamond suit, shows at least a 6-card suit and 8-10 points
Because the 1 opening bid does not convey much information about the length of the diamond suit, we use a jump raise in diamonds, but only with diamonds, the same way we use a jump shift... It's a 6-8-10 hand with diamonds.
This agreement is used over an opening bid of a major also, and is "on" over interference as well. If you want to give this agreement a name, think of it as the 6-8-10 rule.
Responder's Double Jump Shift in a Major
The 6-8-10 call uses a single jump to describe the holding, but a double jump in either major shows 5-5 in both majors - 3 is only invitational while the jump to 3 is forcing to game.
Opener's 2 Rebid
Okay, partner opens 1 and rebids 2... Opener has precisely four diamonds and five or more clubs. (With a 5-5 hand opener would have opened 3NT.)