Abstract:
A data processing system for implementing transaction management of auction-based trading is disclosed. The disclosed data processing system provides a structured trading protocol implemented through a sequence of trading paradigms. The system employs a distributed computer processing network linking together a matching engine and a plurality of workstations. The protocol and its programmed controlling logic enhances trading efficiency, rewards market makers, and fairly distributes market opportunity to system users. In some preferred embodiments, the structured trading protocol permits traders to enter hidden bids or offers during a clearing period that may be converted to transactable bids and offers when the clearing period terminates. In addition, in some preferred embodiments, the structured protocol permits traders to enter orders that specify an initial price and a better, hidden price. The system is programmed to improve the price of a trader&#39;s order within the cap established by the hidden price in particular circumstances in order to permit the trader to maintain priority in the order book when a better-priced order enters the market.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation of application Ser. No. 11/431,293, filed May 9, 2006, which is hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     In many markets, buy and sell orders at the same price are automatically matched. Thus, for example, a first order to buy an item at a price of 100 and a second order to sell the same item at a price of 100 will, in such markets, result in a transaction in which some quantity of the item is sold at the specified price. 
     But in some markets, most notably the secondary market for U.S. government treasuries, orders of equal price are not automatically matched. Rather, certain types of buy and sell orders, called “passive” orders, may co-exist at the same price without triggering a transaction. These passive orders do not trade unless “aggressed” against by a trader submitting a second type of order, called an “aggressive” order. Historically, a passive order to buy has been referred to as a “bid,” while a passive order to sell has been referred to as an “offer.” By contrast, an aggressive order to sell has been referred to as a “hit,” while an aggressive order to buy has been referred to as a “take” or “lift.” 
     This distinction between passive and aggressive orders is one of several characteristics of the secondary market in U.S. government treasuries that developed to encourage market liquidity. In particular, since it is impossible to generate liquidity in a market without having someone first make a price, brokers historically sought to encourage traders to submit bids and offers by not charging them a commission if their orders resulted in a trade. Thus, passive bids and offers could not be matched even at the same price since neither the buyer nor the seller would pay commission. 
     In addition to commission-free trades, brokers in the secondary market for U.S. government treasuries also rewarded passive buyers and sellers by developing a number of trading protocols or conventions which granted passive buyers and sellers certain trading options or “rights.” One such convention is commonly referred to as “workup.” In general terms, this convention permits buyers and sellers to “work up” the size of a trade from the quantity traded as a result of an initial “hit” or “lift.” Typically, certain traders, including the first aggressive-side and passive-side traders, are granted an option or right to increase their size, and to trade that additional size ahead of other traders in the queue. 
     Another popular convention in the secondary market for U.S. government securities is commonly referred to as “clearing time.” In the clearing time convention, when a passive bid or offer is received in the market that is better in terms of price than the best existing passive order on that side of the market, the trader with the best pending passive order on the opposite side of the market is given priority to aggress against the new order before other traders. If this trader chooses not to aggress against the new passive order within a period of time, other traders with pending passive orders may be given that privilege in certain circumstances depending on the particular version of the clearing time convention implemented. If no trader with clearing time privileges aggresses against the new price-improving order, the new order “clears” and can be hit or lifted by any trader. 
     Before the advent of electronic trading, voice brokers implemented the clearing time convention by calling those traders with pending passive orders when the brokers received a new, price-improving passive order on the opposite side of the market, and asking them whether they wished to aggress against the new passive order. This practice was colloquially referred to as “clearing to the offer” in the case of a new, price-improving bid, and “clearing to the bid” in the case of a new, price-improving offer. Only after those traders with clearing privileges failed to respond or declined to aggress against the new passive order were other participants permitted to hit or take the new bid or offer. 
     As electronic trading has become more popular, some electronic platforms have been programmed to provide automated versions of the clearing time convention. In these electronic implementations, the convention is typically implemented by designating the order as “uncleared” and starting a clearing timer for a specified period of time. During the timer&#39;s duration, only the aggressive orders of traders with clearing privileges will be executed. Once the timer expires, the order “clears” and may be traded by anyone. 
     In another aspect of the clearing time convention, when a trader without the current right to aggress against an uncleared bid or offer submits a “hit” or “take” order, this action preserves for the trader the right to do the trade once the bid or offer clears. This has historically been referred to as “hit when” in the case of an aggressive order to sell submitted by a seller without priority, and as a “take when” in the case of an aggressive order to buy a security submitted by a trader without priority. But although the clearing time protocol provides a mechanism by which traders without priority may enter aggressive orders, it does not provide a mechanism by which traders without priority may enter passive orders at prices better than that established by an uncleared bid or offer. Rather, during the clearing time period, other traders wishing to submit such passive bids or offers are blocked from doing so. 
     BRIEF SUMMARY OF THE INVENTION 
     A data processing system for implementing transaction management of auction-based trading is disclosed. The disclosed data processing system provides a structured trading protocol implemented through a sequence of trading paradigms. The system employs a distributed computer processing network linking together a matching engine and a plurality of workstations. The protocol and its programmed controlling logic enhances trading efficiency, rewards market makers, and fairly distributes market opportunity to system users. 
     In some preferred embodiments, the structured trading protocol permits traders to enter hidden bids or offers during a clearing period that may be converted to transactable bids and offers when the clearing period terminates. In addition, in some preferred embodiments, the structured protocol permits traders to enter orders that specify an initial price and a better, hidden price. The system is programmed to improve the price of a trader&#39;s order within the cap established by the hidden price in particular circumstances in order to permit the trader to maintain priority in the order book when a better-priced order enters the market. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a block diagram depicting aspects of a preferred embodiment of the present system; 
         FIGS. 2A-E  are flow diagrams illustrating aspects of system operation in processing a received order in a preferred embodiment; 
         FIGS. 3A-D  are flow diagrams illustrating aspects of system operation in processing termination of a clearing period in one preferred embodiment; 
         FIGS. 4A-D  are flow diagrams illustrating aspects of system operation in processing termination of a clearing period in another preferred embodiment; 
         FIGS. 5A-B  is a flow diagram illustrating aspects of system operation in processing orders specifying hidden prices in a preferred embodiment; and 
         FIGS. 6A-G  depict an illustrative example of system operation in the preferred embodiment of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , there is shown a system  100  comprising a matching engine  102  and a plurality of customer terminals  104  connected via appropriate communication links  106 . Matching engine  102  is preferably adapted to receive orders to buy and sell securities from terminals  104 , to process trading orders in accordance with specified protocols, and to communicate market information concerning trading activity to terminals  104 , as described in more detail below. 
     Matching engine  102  preferably comprises one or more server computers and associated components programmed to implement the trading activity described below. As further shown in  FIG. 1 , matching engine  102  preferably maintains an order book  108  that stores orders received by matching engine  102  from terminals  104 , as described in more detail below. 
     Each terminal  104  may preferably be a computer workstation comprising a CPU, memory, a display, and input devices, such as a mouse, keyboard, or specialized trading keypad. Terminals  104  may be provided to customers for direct entry of buy and sell orders on their own behalf, or to brokers for entry of such orders on behalf of others. Communication links  106  may comprise any appropriate arrangement of wired or wireless communication lines or networks, such as the Internet or dedicated communication lines. 
     One preferred embodiment for processing trade orders in accordance with the present invention will now be described in connection with  FIGS. 2A-E . For ease of description, it will be assumed in the following discussion that the received order is a buy order unless otherwise indicated. It will be recognized, however, that the principles described below may be equally applied where the received order is a sell order. 
     Turning to  FIGS. 2A-E , at step  202 , matching engine  102  receives an order to buy securities from a customer or broker entered via a terminal  104 . At step  204 , matching engine  102  determines whether the order is a passive order (i.e., a bid) or an aggressive order (i.e., a take). If the order is a bid (step  204 , Passive), processing proceeds to step  206  where matching engine  102  determines whether there exists an uncleared offer on the opposite (i.e., sell) side of the market. 
     If there is an uncleared offer (step  206 , Yes), matching engine  102  determines whether the new passive order is at a price that is equal to, better than, or worse than the current best bid (step  208 ). If the price of the new order is equal to the current best price (step  208 , Equal), the new passive order is preferably rejected since passive orders at the best price are typically entitled to clearing privileges vis a vis uncleared passive orders on the other side of the market, and a trader should not be able to obtain such privileges once an uncleared order is displayed to the market (step  210 ). Notably, however, in systems where only the first passive order in the queue is entitled to clearing privileges, subsequent passive orders submitted during a clearing period need not be rejected and may instead be queued on a price-time priority basis. Furthermore, in a system where more than one passive trader in the queue is or may be granted clearing privileges, the system may be programmed to store the new passive order in the order book but not to grant clearing privileges to the trader that submitted it. In addition, where the system operator is not concerned with granting clearing privileges to the new passive bidder or offeror, the new passive bidder or offeror may be permitted to join the order with clearing privileges. For the avoidance of doubt, to queue orders on a price-time priority basis in the context of the present system and method means to queue received orders first on the basis of their price, and then, in the case of tie in price, on the basis of time received. 
     If the price of the new passive order is below the best price in the market (step  208 , Worse), the new order is queued in order book  108  on a price-time priority basis (step  212 ). Alternatively, where the market is one for which no market depth is maintained, orders submitted at worse than the current best price may be rejected. 
     Otherwise, if the new passive order is above the best price in the market (step  208 , Better), the order is stored by matching engine  102  but preferably not entered in order book  108  and not displayed to the market (step  214 ). Passive orders processed according to step  214  will be referred to herein as “bid-when” orders (in the case of passive orders to buy) and “offer-when” orders (in the case of passive orders to sell). 
     In a preferred embodiment, bid-when and offer-when orders may be canceled by the traders that submitted them at any time during the clearing period. Where a plurality of bid-when or offer-when orders are entered, these are preferably stored based on price-time priority. A bid-when or offer-when indicator may be provided, but is preferably displayed only to the traders that have entered bid-when or offer-when orders. Additional aspects of the processing of bid-when and offer-when orders are described below in connection with other portions of  FIGS. 2A-E  and in connection with  FIGS. 3A-D  and  FIG. 4 . 
     Returning to decision step  206 , if there is no uncleared order on the sell side of the market (step  206 , No), matching engine  102  determines whether the new bid is at a better price than the best current bid in the market (Step  216 ). If so (step  216 , Better), the new order is designated uncleared and a clearing timer is started (step  218 ). At step  220 , the received order is entered in order book  108  on a price-time priority basis. As noted above, where the market is one for which no market depth is maintained, orders identified at step  216  as being at worse than the current best price may be rejected. In addition, where the market is one for which only one bid or offer may be submitted at a given price, orders identified at step  216  as being at the current best price may be rejected. 
     Returning next to decision step  204 , if the received order is an aggressive order (step  204 , Aggressive), matching engine  102  determines whether the order seeks to aggress against an uncleared offer (step  222 ). More specifically, in a preferred embodiment, matching engine  102  determines whether an unexpired clearing timer for the sell side of the market has been set and is running. 
     If the passive offer to be matched is cleared (step  222 , Cleared), the aggressive order and the pending passive order are matched (step  224 ). Processing proceeds to step  226  where the trade may be worked up in accordance with any desired workup protocol implemented by the system. 
     Otherwise, if the order against which the aggressor seeks to aggress is uncleared (step  222 , Uncleared), processing proceeds to step  228  where matching engine  102  determines whether the aggressor has priority to aggress against the uncleared order, i.e., whether the aggressor is the trader that submitted the best pending passive order on the opposite side of the market (or, in systems that grant clearing privileges to multiple passive parties, whether all passive traders with clearing privileges ahead of the aggressor have given up or otherwise lost those rights. 
     If the aggressor is not currently entitled to execute the transaction (step  228 , No), a “take when” situation is created (step  230 ). As known in the art, in a “take when” situation, the aggressive take order is not executed but is instead held pending expiration of the clearing rights of all traders ahead of the aggressor. If none of those traders elect to aggress against the uncleared order and their clearing rights expire, then the pending aggressive take-when order will be executed, as discussed in more detail in connection with  FIGS. 3 and 4  below. 
     Otherwise, if the aggressor is entitled to hit the pending uncleared bid (step  228 , Yes), the transaction is executed at step  232 . At step  234 , all pending bid-when and offer-when orders are canceled. At step  236 , if any of these canceled orders were on the opposite side of the market from the aggressor (i.e., if they were offer-when orders in the present example), matching engine  102  preferably adds the traders who submitted those orders to the list of buyers or sellers on the passive side of the market at the execution price based on the price-time priority of their bid-when or offer-when orders. For example, if the passive side of the market included two offers that were taken by the aggressor (ranked first and second on the basis of price-time priority), and there were also stored in the system two pending offer-when orders (ranked first and second on the basis of price-time priority), the system preferably establishes the list of sellers as: (1) the trader that submitted offer #1; (2) the trader that submitted offer #2; (3) the trader that submitted offer-when order #1; and (4) the trader that submitted offer-when order #2. Processing then proceeds to step  238  where the trade may be worked up in accordance with any desired workup protocol implemented by the system. 
       FIG. 3  is a flow diagram illustrating one preferred embodiment of system processing when a clearing period terminates. For ease of description, it will be assumed in the following discussion that the passive order clearing to the market is a sell-side order (i.e., an offer) unless otherwise indicated. It will be recognized, however, that the principles described below may be equally applied to cases where the passive order clearing to the market is a bid. 
     Turning to  FIG. 3 , at step  302 , a clearing period terminates. At step  304 , the system determines whether the clearing period terminated because of: (a) expiration of a clearing timer without trading activity, or (b) as a result of an aggressive order from the uncleared side of the market, i.e., a hit in this example. If the clearing period terminated because of an aggressive order from the uncleared side of the market (step  304 , Aggressive Order), the system terminates the clearing timer (step  306 ), executes the aggressive order (step  308 ), and cancels any pending bid-when orders (step  310 ). Processing proceeds to step  312  where the trade may be worked up in accordance with any desired workup protocol implemented by the system. 
     Otherwise, if the clearing period terminated because of expiration of a clearing timer without trading activity (step  304 , Expiration), the system determines whether a take-when order is waiting to be executed (step  314 ). In a preferred embodiment, this branch of system processing is also followed where the clearing period terminates for other reasons such as where the trader with clearing privileges modifies his or her order but does not hit or take the uncleared order as to which he or she has priority, cancels his or her order, or expressly clears the uncleared order as to which he or she has priority. 
     If a take-when order is waiting to be executed (step  314 , Yes), the take-when order is executed and a transaction occurs (step  316 ). At step  318 , all pending bid-when and offer-when orders are cancelled. At step  320 , if any of these canceled orders were on the opposite side of the market from the aggressor, matching engine  102  preferably adds the traders who submitted those orders to the list of buyers or sellers on the passive side of the market based on the time-price priority of their bid-when or offer-when orders, in the manner described above. Processing proceeds to step  322  where the trade may be worked up in accordance with any desired workup protocol implemented by the system. 
     Otherwise, if there are no waiting take-when orders to be executed (step  314 , No), the system determines whether there are any pending bid-when orders that had been stored during the clearing period (step  324 ). If there are no pending bid-when orders (step  324 , No), the offer clears and an open bid-offer market results in which any trader may aggress against the newly-cleared offer (step  326 ). 
     Otherwise, if there are pending bid-when orders (step  324 , Yes), the bid-when orders are converted to bids at their specified prices and queued in order book  108  based on their price-time priority (step  328 ). As will be recognized, in the preferred embodiment of the present invention, the best pending price at this stage of system processing will always represent an improvement over the best previously pending price on the same side of the market, either because (1) the trader with clearing privileges improved the price of his or her order to a price that is better than the prices of all bid-when orders, in which case that trader remains the best bid, but at a higher price that should be cleared to the opposite side of the market; or (2) the trader with clearing privileges did not improve the price of his or her order to a price that is better than the prices of all bid-when orders, in which case the new highest priority bid in the market will be the converted bid-when order with the highest price-time priority and should be cleared to the opposite side of the market. Thus, in scenario (1) above, the original best bid&#39;s new higher-priced order is preferably designated as uncleared while in scenario (2) above, the converted bid-when order with the highest price-time priority is e preferably designated as uncleared, and, in both scenarios, a new clearing timer is commenced to clear the new uncleared bid to the recently cleared offer on the opposite side of the market (step  330 ). In a preferred embodiment, if conversion of a bid-when or offer-when order to a bid or offer would create a reverse market, the bid-when or offer-when order is cancelled and not converted. 
     The preferred embodiment of  FIGS. 2 and 3  will now be further described by way of two illustrative examples. 
     EXAMPLE 1 
     1. A bids @ 4 
     2. B offers @ 7 
     3. C bids-when @ 6 
     4. D bids-when @ 5 
     5. E takes-when B&#39;s 7 offer 
     6. the clearing timer expires 
     Upon expiration of the clearing timer, Trader E&#39;s take-when order will execute, and the two bid-when orders of Trader C and Trader D are canceled. 
     EXAMPLE 2 
     1. A bids @ 4 
     2. B offers @ 7 
     3. C bids-when @ 5 
     4. D bids-when @ 6 
     5. E hits A&#39;s 4 bid 
     In this example, Trader E&#39;s hit is executed and the two bid-when orders of Trader C and Trader D are canceled. Trader D is designated second buyer and Trader C is designated third buyer. As noted above, because Trader D&#39;s bid-when order was at a better price than that of Trader C, Trader D becomes the second buyer behind Trader A. Had both Trader D and Trader C bid-when at the same price, time priority would have controlled their order in the buyer queue. 
       FIG. 4  is a flow diagram illustrating another preferred embodiment of system processing when a clearing period terminates. This preferred embodiment is designed to provide the current best bid/best offer with protection against being replaced as the best price in the market as a result of a bid-when/offer-when order. Specifically, in this preferred embodiment, a trader entering a passive order may specify a first price at which the trader wishes the order to be displayed in the first instance, and a higher hidden price, at which the trader wishes the order to be displayed if the original price is bettered in the market. As above, it will be assumed in the following discussion that the passive order clearing to the market is a sell-side order (i.e., an offer) unless otherwise indicated. It will be recognized, however, that the principles described below may be equally applied to cases where the passive order clearing to the market is a bid. 
     Turning to  FIG. 4 , at step  402 , a clearing period terminates. At step  404 , the system determines whether the clearing period terminated because of: (a) expiration of a clearing timer without trading activity, or (b) as a result of an aggressive order from the uncleared side of the market (i.e., a hit in this example). If the clearing period terminated because of an aggressive order from the uncleared side of the market (step  404 , Aggressive Order), the system terminates the clearing timer (step  406 ), executes the aggressive order (step  408 ), and cancels any pending bid-when orders (step  410 ). Processing proceeds to step  412  where the trade may be worked up in accordance with any desired workup protocol implemented by the system. 
     Otherwise, if the clearing period terminated because of expiration of a clearing timer without trading activity (step  404 , Expiration), the system determines whether a take-when order is waiting to be executed (step  414 ). In a preferred embodiment, this branch of system processing is also followed where the clearing period terminates for other reasons such as where the trader with clearing privileges modifies his or her order but does not hit or take the uncleared order as to which he or she has priority, cancels his or her order, or expressly clears the uncleared order as to which he or she has priority. 
     If a take-when order is waiting to be executed (step  414 , Yes), the take-when order is executed and a transaction occurs (step  416 ). At step  418  all pending bid-when and offer-when orders are cancelled. At step  420 , if any of these cancelled were on the opposite side of the market from the aggressor, matching engine  102  preferably adds the traders who submitted those orders to the list of buyers or sellers on the passive side of the market based on the time-price priority of their bid-when or offer-when orders, in the manner described above. Processing proceeds to step  422  where the trade may be worked up in accordance with any desired workup protocol implemented by the system. 
     Otherwise, if there are no waiting take-when orders to be executed (step  414 , No), the system determines whether there are any pending bid-when orders that had been stored during the clearing period (step  424 ). If there are no pending bid-when orders (step  424 , No), the offer clears and an open bid-offer market results in which any trader may aggress against the newly-cleared offer (step  426 ). 
     Otherwise, if there are pending bid-when orders (step  424 , Yes), the bid-when orders are converted to bids at their specified prices and queued in order book  108  based on their price-time priority (step  428 ). At step  430 , matching engine  102  determines whether the previous best bid in the market had specified a hidden price for its order higher than the price that was displayed to the market. If so (step  430 , Yes), matching engine  102  increases the price of that bid (step  432 ). In one preferred embodiment, the price of the bid may be increased to the lower of: (a) the highest hidden price specified by the trader; or (b) the new best price specified in a bid-when order. In a second preferred embodiment, the price of the trader&#39;s bid may be increased to the lower of: (a) the highest hidden price specified by the trader; or (b) the new best price specified in a bid-when order plus some increment. In some preferred embodiments, the price of the trader&#39;s bid may be increased only if the bid&#39;s specified hidden price is high enough such that it can return the trader&#39;s bid to first in the market. 
     As will be recognized, in the preferred embodiment of the present invention, the new best price in the market (whether that of the trader that submitted a converted bid-when order or the original high bidder whose hidden price returned its original bid to the top of the queue) will always represent an improvement over the best pending price on the same side of the market. Thus, the new highest priority bid is preferably designated as uncleared, and a new clearing timer is commenced to clear this bid to the recently cleared offer on the opposite side of the market (step  434 ). 
     The preferred embodiment of  FIGS. 2 and 4  will now be further described in connection with an illustrative example: 
     EXAMPLE 1 
     1. A bids @ 4, hidden price of 7 
     2. B offers @ 8 
     3. C bids-when @ 6 
     4. D bids-when @ 5 
     5. the clearing timer expires 
     Upon expiration of the clearing timer, the two bid-when orders of Trader C and Trader D are converted to regular bids at prices of 6 and 5, respectively. However, because Trader A bid with a maximum hidden price of 7, his bid will be re-priced to outbid that of Trader C and will be placed at the head of the queue, either at a price of 6 or at a price some specified increment above 6, depending on the preferred embodiment selected. 
     In a preferred embodiment, bid-when orders and offer-when orders may also be permitted to specify a hidden price. As will be recognized, in such a preferred embodiment, a “bidding war” may transpire when a bid-when or offer-when order is first converted to a regular bid or offer, and it may take several iterations of price increases to reach a new market steady state. 
     In other preferred embodiments of the present invention, the concept of hidden prices may be applied more generally in any two-sided market, whether or not the market implements a clearing time convention and whether or not the market distinguishes between passive and aggressive orders. A preferred embodiment for implementing hidden-price functionality in a First-In-First-Out (FIFO) market in which no clearing time or workup convention is employed, and in which all buy and sell orders are automatically matched if their prices are the same, will now be described in connection with  FIG. 5 . For ease of description, it will be assumed in the following discussion that the new order received for processing is a buy order. It will be recognized, however, that the principles described below may be equally applied to cases where the new order received for processing is a sell order. 
     Turning to  FIG. 5 , in step  502 , a new buy order is received by matching engine  102  entered by a trader or broker via a terminal  104 . In step  504 , the new buy order is queued on a price-time priority basis in order book  108 . At step  506 , matching engine  102  determines whether the new order improves on the best buy price in order book  108 : If it does (step  506 , Yes), matching engine  102  determines whether the previously best-priced buy order in order book  108  specifies a hidden price greater than the price shown to the market (step  508 ). If it does (step  508 , Yes), matching engine  102  will attempt to increase the price of the previously best-priced order to return it to first in the buy-side order queue (step  510 ). As above, matching engine  102  may be programmed to increase the price of the previously best-priced buy order (assuming the hidden-size cap permits) to: (a) equal the price of the new buy order; or (b) greater than the price of the new buy order by a specified amount. Furthermore, matching engine  102  may be programmed to increase the size of the previously best-priced order only if that increase will be adequate to return the order to first place in the buy-side order queue. 
     At step  512 , matching engine  102  determines whether the improved price (whether resulting from the newly submitted order, an hidden-price improvement in the previously best-priced order, or both) causes a match with a pending order on the opposite side of the market. If so (step  512 , Yes), orders at the same price are matched to the extent their quantities match (step  514 ). 
     As will be recognized, because the trading logic of  FIG. 5  is preferably applied on both the buy and sell side of the market, a “bidding war” on both sides of the market may simultaneously occur resulting in a more rapid convergence of the market to a price at which both buyers and sellers are willing to transact or to a significantly smaller spread than might otherwise occur, thus promoting market liquidity. 
     Operation of this preferred embodiment will now be described in connection with an illustrative example shown in  FIGS. 6A-G . Beginning with  FIG. 6A , it is assumed for purposes of the present example that a Trader “A” enters a buy order for a quantity of 10 at a price of 1 with a hidden price maximum of 4. In  FIG. 6B , Trader “B” enters a sell order for a quantity of 5 at a price of 8 with a hidden price minimum of 5. For purposes of the present example, it is assumed that the market for this item is a FIFO market and no clearing of the new sell order to the existing buy order is necessary, i.e., the new sell order is immediately transactable by any trader. 
     Continuing with the example, in  FIG. 6C , Trader “C” enters a buy order for a quantity of 5 at a price of 3, but with no hidden price specified. As a result, the price of Trader A&#39;s order is increased to a price of 3 to match that of Trader C (since that is within the hidden price maximum of 4 specified for the order by Trader A), and the two orders are maintained in the order book with Trader A&#39;s order maintaining priority. As will be recognized, the present example implements the preferred embodiment described above in which the price of Trader A&#39;s order is increased only to match that of Trader C, not beyond it. 
     In  FIG. 6D , Trader “D” enters a sell order for a quantity of 15 at a price of 6 with a hidden price of 5. As a result, the price of Trader B&#39;s order is decreased to 6 (since that is within the hidden price minimum of 5 specified for the order by Trader B), and the two orders are maintained in the order book with Trader B&#39;s order maintaining priority. 
     In  FIG. 6E , Trader “E” enters a buy order for a quantity of 5 at a price of 4 with no hidden price specified. As a result, the price of Trader A&#39;s order is increased to a price of 4 to match that of Trader E (since that is within the hidden price maximum of 4 specified for the order by Trader A), and the two orders are maintained in the order book with Trader A&#39;s order maintaining priority. Trader C&#39;s order is also maintained in the order book, but at a lower priority on the basis of its lower price. 
     In  FIG. 6F , Trader “F” enters a sell order for a quantity of 25 at a price of 4 with no hidden price. This price matches the orders of Trader A and Trader E and thus triggers a transaction for Trader A&#39;s quantity of 10 and Trader E&#39;s quantity of 5. As will be recognized, the present example implements the preferred embodiment described above in which the prices of Trader B&#39;s and Trader D&#39;s orders are not decreased from 6 to 5 despite Trader F&#39;s order at a price of 4, since improving the price of those orders would not return either B or D to first position in the queue. 
     As shown in  FIG. 6G , after execution of this transaction, the only order remaining on the buy side of the market is that of Trader C at a price of 3. On the sell side, Trader F has an order at 4 for his remaining quantity of 10, and Trader B&#39;s and Trader D&#39;s orders at 6 also remain in the order book. 
     While the present invention has been described in conjunction with specific embodiments, it is evident that numerous alternatives, modifications, and variations will be apparent to those skilled in the art in view of the foregoing description.