Patent Publication Number: US-9430722-B2

Title: Control apparatus, control method, and storage medium to notify users of sheet holding units

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 14/452,409, filed on Aug. 5, 2014, which claims priority from Japanese Patent Application No. 2013-165349, filed Aug. 8, 2013, all of which are hereby incorporated by reference herein in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a control apparatus that can store a print job and execute the stored print job. Further, the present invention relates to a related control method and a storage medium. 
     2. Description of the Related Art 
     As discussed in Japanese Patent Application Laid-Open No. 2010-284919, it is conventionally known that a printing apparatus includes a plurality of sheet holding units and an operation screen can notify a user that attribute information (e.g., sheet size) about a sheet to be used in a print job is not registered to any one of the sheet holding units. 
     Further, as discussed in Japanese Patent Application Laid-Open No. 2010-49167, it is conventionally known that an operation screen can display a list of print job status information, so that a user can know that the size of a sheet to be used in a print job is not registered to any one of a plurality of sheet holding units or that the remaining amount of sheets to be used in a print job is zero. 
     If attribute information about a sheet to be used in a print job is not registered to any one of a plurality of sheet holding units, the execution of the print job will be stopped. In such a case, to prevent the execution of the print job from being stopped, it is required for a user to change sheet attribute information registered to any one of the sheet holding units to the attribute information about the sheet to be used in the print job. In this case, attribute information about a sheet holding unit to be used in another print job may be changed unintentionally and accordingly the execution of another print job may stop. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, a printing apparatus includes a job holding unit configured to hold jobs, wherein each of the jobs is configured to perform printing an image on a sheet which is conveyed from at least one of sheet holding units, a selecting unit configured to select a job from among the jobs held by the job holding unit, a receiving unit configured to receive, from a user, an execution instruction to execute the job selected by the selecting unit, a performing unit configured to perform the job for which the execution instruction is received by the receiving unit, a displaying unit configured to display a screen for selecting at least one of the sheet holding units for which attribute information of a sheet, to be used in a first job selected by the selecting unit, is to be stored, and a notification unit configured to notify, on the screen in a distinguishable manner, a user of at least one of the sheet holding units which is used in printing of a second job and at least one of the sheet holding units which is not used in printing of the second job. 
     When attribute information about a sheet to be used in a target print job is registered to none of sheet holding units provided in a printing apparatus, it is necessary to change sheet attribute information registered to any one of the sheet holding units to the attribute information about the sheet to be used in the target print job. A control apparatus performs control in such a way as to prevent attribute information about a sheet to be used in a first job from being stored for a sheet holding unit in which attribute information about a sheet to be used in a second job selected at earlier timing than the first job corresponds to sheet attribute information stored in a storage unit. Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a digital printing system according to a first exemplary embodiment of the present invention. 
         FIG. 2  is a functional block diagram illustrating a functional configuration of a digital printing machine according to the first exemplary embodiment. 
         FIG. 3  is a block diagram illustrating a hardware configuration of a computer (PC) according to the first exemplary embodiment. 
         FIG. 4  is a plan view illustrating an operation unit of the digital printing machine according to the first exemplary embodiment. 
         FIG. 5A  illustrates a data content of an entry according to the first exemplary embodiment,  FIG. 5B  illustrates an entry related print queue buffer content of an entry according to the first exemplary embodiment, and  FIG. 5C  illustrates a data content of an entry related hold queue buffer according to the first exemplary embodiment. 
         FIG. 6  is a flowchart illustrating sequential processing relating to media mismatch determination, which can be performed by the digital printing machine according to the first exemplary embodiment. 
         FIG. 7  is a flowchart illustrating media mismatch determination processing (see step S 700 ) illustrated in  FIG. 6 , which can be performed by the digital printing machine according to the first exemplary embodiment. 
         FIG. 8  is a flowchart illustrating media mismatch determination processing (see step S 800 ) illustrated in  FIG. 7 , which can be performed by the digital printing machine according to the first exemplary embodiment when the target print job is a sheet type designated job. 
         FIG. 9  is a flowchart illustrating media mismatch determination processing (see step S 900 ) illustrated in  FIG. 7 , which can be performed by the digital printing machine according to the first exemplary embodiment when the target print job is a sheet holding unit designated job. 
         FIG. 10  is a flowchart illustrating media mismatch determination result notification processing (see step S 1000 ) illustrated in  FIG. 6 , which can be performed by the digital printing machine according to the first exemplary embodiment. 
         FIG. 11  is a flowchart illustrating sheet setting processing (see step S 1100 ) illustrated in  FIG. 6 , which can be performed by the digital printing machine according to the first exemplary embodiment. 
         FIG. 12  is a flowchart illustrating sheet holding unit selection screen display processing (see step S 1200 ) illustrated in  FIG. 11 , which can be performed by the digital printing machine according to the first exemplary embodiment. 
         FIG. 13  is a flowchart illustrating sheet holding unit attribute information setting processing (see step S 1300 ) illustrated in  FIG. 11 , which can be performed by the digital printing machine according to the first exemplary embodiment. 
         FIG. 14A  illustrates an example of a job hold function operation screen that can be displayed on the operation unit of the digital printing machine according to the first exemplary embodiment,  FIG. 14B  illustrates another example of the job hold function operation screen that can be displayed on the operation unit of the digital printing machine according to the first exemplary embodiment, and  FIG. 14C  illustrates another example of the job hold function operation screen that can be displayed on the operation unit of the digital printing machine according to the first exemplary embodiment. 
         FIG. 15A  illustrates an example of a sheet setting screen (mismatch sheet list screen) that can be displayed on the operation unit of the digital printing machine according to the first exemplary embodiment, and  FIG. 15B  illustrates an example of a sheet setting screen (sheet holding unit selection screen) that can be displayed on the operation unit of the digital printing machine according to the first exemplary embodiment, and  FIG. 15C  illustrates an example of a sheet setting screen (sheet details information screen) that can be displayed on the operation unit of the digital printing machine according to the first exemplary embodiment. 
         FIG. 16A  illustrates an example of a warning screen that can be displayed on the operation unit of the digital printing machine according to the first exemplary embodiment, and  FIG. 16B  illustrates an example of a notification screen that can be displayed on the operation unit of the digital printing machine according to the first exemplary embodiment. 
         FIG. 17A  illustrates an example of a sheet management table that can be used to manage the information about a sheet stored in each sheet holding unit of the digital printing machine according to the first exemplary embodiment, and  FIG. 17B  illustrates an example of information about sheets to be used in a plurality of jobs in the digital printing machine according to the first exemplary embodiment. 
         FIG. 18  illustrates a sheet holding unit related determination result, which can be obtained by the digital printing machine according to the first exemplary embodiment. 
         FIG. 19  is a flowchart illustrating sheet holding unit selection screen display processing (see step S 1200 ) illustrated in  FIG. 11 , which can be performed by the digital printing machine according to a second exemplary embodiment. 
         FIG. 20  illustrates a sheet holding unit related determination result, which can be obtained by the digital printing machine according to the second exemplary embodiment. 
         FIG. 21  illustrates an example of a sheet holding unit selection screen that can be displayed on the operation unit of the digital printing machine according to the second exemplary embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to attached drawings. The following description of the exemplary embodiments does not intend to limit the scope of the present invention. Further, although the following exemplary embodiments include various characteristic features, it should be construed that all of the described features and their combinations are not always necessary to constitute the essential features of the present invention. 
     A digital printing system according to a first exemplary embodiment of the present invention is described in detail blow with reference to  FIG. 1 . The printing system illustrated in  FIG. 1  includes a digital printing machine (i.e., a printing apparatus)  102  and a computer  101 , which are connected to each other via a network  100 . 
     The digital printing machine  102  includes a plurality of apparatuses having unique roles, which are mutually connected and constituted in such a way as to perform complicated sheet processing. 
     The digital printing machine  102  can be roughly divided into three sections, one of which is a printer unit  1000 . As illustrated in  FIG. 1 , there is a plurality of sheet holding apparatuses disposed on the right side of the printer unit  1000 . The main role of each sheet holding apparatus is successively supplying sheets stored therein to the printer unit  1000  at appropriate timing. Further, each sheet holding apparatus is equipped with a sensor (not illustrated) that can detect the remaining amount of sheets stored therein. The printer unit  1000  includes a sheet holding unit  231 , which is functionally operable as a built-in sheet holding apparatus. In the following description, the sheet holding unit of the printer unit  1000  is referred to as the sheet holding apparatus. Each constituent component of the digital printing machine  102  is described in detail below. 
     The printer unit  1000  can form (or print) a toner image on a recording medium (e.g., a sheet), which can be supplied from the sheet holding unit, based on image data. The printer unit  1000  has the following configuration and can operate in the following manner. 
     The printer unit  1000  irradiates a photosensitive drum with scanning light, such as a laser beam, which has been modulated based on the image data and reflected by a rotary polygon mirror. The printer unit  1000  develops an electrostatic latent image with toner particles after the latent image is formed on the photosensitive drum, and transfers a developed toner image onto a sheet pressed against a transfer drum. The printer unit  1000  sequentially performs the above-mentioned sequential image forming processes using yellow (Y), magenta (M), cyan (C), and black (K) toners to form a full-color image on the sheet. Further, the toner colors to be used by the printer unit  1000  are not limited to the above-mentioned four colors. For example, the toner colors that the printer unit  1000  can use include special colors in addition to the above-mentioned four colors. Further, the printer unit  1000  can be configured to transfer transparent toners. The printer unit  1000  conveys the printed sheet, after the above-mentioned full-color image has been formed thereon, from the transfer drum to a fixing device. The fixing device includes rollers and belts. The fixing device includes a heat source (e.g., a halogen heater) incorporated in the roller and can apply heat and pressure to melt and fix the image on the sheet after the image has been transferred on the sheet. The printer unit  1000  is not limited to an electrophotographic type and can be any other printer, such as an inkjet printer or a thermal transfer printer. 
     The printer unit  1000  of the digital printing machine  102  according to the first exemplary embodiment includes a scanner (not illustrated) and an operation unit  204  (see  FIG. 4 ) that are disposed on an upper surface of the printer unit  1000 . The operation unit  204  is not illustrated in  FIG. 1  because the operation unit  204  is disposed on the upper surface of the printer unit  1000 . The operation unit  204  provides various interfaces that allow a user to perform various settings and operations for the printer unit  1000  according to the first exemplary embodiment. The printer unit  1000  further includes a document feeder  224  that is provided on a main body thereof together with the scanner. 
     Further, the digital printing machine  102  is configured to have various attachable optional apparatuses in addition to the printer unit  1000 . 
     Each of mass-storage sheet holding apparatuses  221 ,  222 , and  223  is an example of the sheet holding apparatus that is directly or indirectly attachable to and detachable from the printer unit  1000 . These sheet holding apparatuses include a plurality of sheet holding units  233  to  241 . Each of a plurality of sheet holding units  233  to  241  is equipped with a sensor that can detect the remaining amount of sheets stored therein. The printer unit  1000  having the above-mentioned configuration can perform print processing on massively stored sheets. Although the printing system illustrated in  FIG. 1  includes only three mass-storage sheet holding apparatuses  221 ,  222 , and  223  that are sequentially connected, the number of the sheet holding apparatuses is not limited to the illustrated example. The printing system can be configured to include only one mass-storage sheet holding apparatus  221 . Further, each of the plurality of sheet holding units can be a paper feed tray or a manual feed tray. For example, at least one manual feed tray can be combined with two or more paper feed trays. 
     Each of mass-storage stackers  225  and  226  is an apparatus that can stock printed sheets. The system including the above-mentioned mass-storage sheet holding apparatuses generates massive print products. This is the reason why the system requires the above-mentioned mass-storage stackers. However, the number of the mass-storage stackers and the number of the mass-storage sheet holding apparatuses are not limited to the configuration illustrated in  FIG. 1 . Although the printing system illustrated in  FIG. 1  includes only two mass-storage stackers  225  and  226  that are sequentially connected, the number of the stackers is not limited to the illustrated example. For example, the printing system illustrated in  FIG. 1  can be configured to include only one mass-storage stacker  225 . 
     Each of the mass-storage stackers  225  and  226  includes a door that can be opened to take stacked sheets out of an internal stacking tray in response to a user&#39;s instruction operation. Further, the door of each mass-storage stacker can be automatically opened in response to an instruction from the printer unit  1000 . Before the printing system performs the above-mentioned door opening operation, the printing system stops the processing to stack printed sheets to respective mass-storage stackers  225  and  226 . 
     Further, when respective mass-storage stackers  225  and  226  stack printed sheets, the mass-storage stackers  225  and  226  can shift the stacking position of an arbitrary sheet. This function is referred to as a shift paper output function. A predetermined amount of massively stacked sheets can be sorted to form a single bundle. 
     A folding apparatus  232  is an apparatus that can perform various folding processing (e.g., center folding, Z folding, three-part folding, and four-part folding) on each sheet. 
     A saddle stitch bookbinding machine  227  includes various units that can perform staple processing, saddle stitch or saddle folding processing (required to output bookbinding products), punch processing, and shift paper output processing, on sheets printed by the printer unit  1000 . When the saddle stitch bookbinding machine  227  generates a saddle stitch binding output product, the digital printing machine  102  described in the first exemplary embodiment forms the output product by combining a saddle folding function and a saddle stitch function of the saddle stitch bookbinding machine  227 , without using a folding function of the folding apparatus  232 . 
     A sheet cutting apparatus  230  is an apparatus that can convey a bookbinding output product, after the output product is stitched by the saddle stitch bookbinding machine  227 , and can cut a predetermined edge region corresponding to the front edge portion to finish the front edge to have a flat surface. 
     An inserter  228  can hold an arbitrary sheet and insert the held sheet into a plurality of sheets supplied from the printer unit  1000  at appropriate timing, based on settings. For example, the inserter  228  can insert a sheet that does not require any printing into printed sheets. The inserter  228  includes a plurality of mass-storage sheet holding portions, which are similar to the mass-storage sheet holding apparatuses  221 ,  222 , and  223 , so that the digital printing machine  102  can realize mass-storage print processing. 
     A case bookbinding machine  229  is an apparatus that can perform front page pasting processing on a sheet bundle printed by the printer unit  1000  or output from the inserter  228  to form a case bookbinding output product. Further, the case bookbinding machine  229  can perform top paste bookbinding processing, which corresponds to working process to perform pasting and bookbinding without using a front page. 
     The folding apparatus  232 , the saddle stitch bookbinding machine  227 , the sheet cutting apparatus  230 , the inserter  228 , and the case bookbinding machine  229  can be configured to be incorporated in or independent of the digital printing machine  102 . 
     On the other hand, in  FIG. 1 , the mass-storage stackers  225  and  226  (i.e., the devices that stack sheets) and other devices disposed on the left side of the printer unit  1000  are referred to as sheet working apparatuses. The sheet working apparatus may also be referred to as a sheet processing apparatus or a post-processing apparatus. The sheet working apparatus can also apply various working processes to sheets that have been subjected to the print processing. The above-mentioned sheet holding apparatuses and the sheet working apparatuses are collectively referred to as a sheet processing apparatus  200 . 
     Next, a circuit configuration of the digital printing machine  102  according to the first exemplary embodiment is described in detail below with reference to a functional block diagram illustrated in  FIG. 2 . The configuration illustrated in  FIG. 2  can be applied to the above-mentioned sheet processing apparatus, such as the sheet holding apparatuses and the sheet processing apparatuses. 
     The digital printing machine  102  includes a built-in nonvolatile memory (i.e., a storing unit), such as a hard disk drive  209  (hereinafter, referred to as “HDD”), which can store a plurality of jobs (i.e., processing targets). However, the built-in memory of the digital printing machine  102 , which has been employed in the first exemplary embodiment, is not limited to the hard disk drive. For example, the HDD  209  can be replaced by a similar mass-storage and nonvolatile storage apparatus. The HDD  209  can be replaced by a solid state drive (SSD) or a similar nonvolatile memory. 
     Further, the digital printing machine  102  can receive data from the scanner and store the received data in the HDD  209 . Then, the digital printing machine  102  can cause a printer unit  203  to perform printing based on the data read out of the HDD  209 . In other words, the digital printing machine  102  can execute a copy job. Further, the digital printing machine  102  can receive a job from an external apparatus via an external I/F  202  (i.e., an example of a communication unit) and store the received job in the HDD  209 . Then, the digital printing machine  102  can cause the printer unit  203  to perform printing based on the data read out of the HDD  209 . The function of the digital printing machine  102  in this case is referred to as a print function. The digital printing machine  102  is a multi-function peripheral (MFP) having the above-mentioned plurality of functions, which may be referred to as an image forming apparatus. The digital printing machine  102  can perform color print processing or can perform monochrome print processing. 
     The scanner can read an image of a document to be processed and perform image processing on the read image data to output a processed image. The external I/F  202  can transmit and receive image data to and from an external apparatus. For example, the external apparatus is a facsimile, a network connection device, or an external dedicated device. Further, the HDD  209  stores various kinds of management information, which the digital printing machine  102  can permanently store, change, and manage. Further, the digital printing machine  102  includes the printer unit  203  that performs print processing for a print target job stored in the HDD  209 . The operation unit  204  of the digital printing machine  102  includes a display unit, which corresponds to an example of a user interface unit. A controller unit (i.e., a control unit)  205  of the digital printing machine  102  includes a CPU  212 , which can integrally control processing and operations to be performed by various units provided in the digital printing machine  102 . Further, the controller unit (i.e. the control unit) includes a read only memory (ROM)  207  and a random access memory (RAM)  208 , which can be operated as the storing unit. The ROM  207  and the RAM  208  store various control programs, which can be executed by the CPU  212  to execute various processing of flowcharts described in detail below. Further, the ROM  207  stores a display control program, which can be executed by the CPU  212  to display various UI screens on the display unit of the operation unit  204 . 
     The CPU  212  of the controller unit  205  executes programs read out of the ROM  207  to cause the digital printing machine  102  to perform various operations according to the first exemplary embodiment. Further, the CPU  212  interprets page description language (hereinafter, referred to as “PDL”) data when the PDL data is received from an external apparatus via the external I/F  202 . The CPU  212  performs an operation to develop the PDL data into raster image data (bitmap image data). The program that causes the CPU  212  to perform the above-mentioned operations is stored in the ROM  207 . Similarly, a program that causes the CPU  212  to interpret and process a print job received from an external apparatus via the external I/F  202  is stored in the ROM  207 . The above-mentioned operations can be processed by software programs. The ROM  207  is a read only memory that stores a boot sequence program and a font information program beforehand. Various programs stored in the ROM  207  are described in detail below. The RAM  208  is a readable and writable memory, which can store image data received from the scanner and the external I/F  202 , various programs, and setting information. 
     Further, the HDD  209  preliminarily stores various programs described below. Image data compressed by a compression/expansion unit  210  can be also stored in the HDD  209 . The HDD  209  is constituted to store a plurality of pieces of data, including print data of a processing target job. The controller unit  205  can store processing target jobs input via various input units (e.g., the scanner and the external I/F  202 ) in the HDD  209 . The controller unit  205  can read a processing target job from the HDD  209  and output the target job to the printer unit  203  to cause the printer unit  203  to perform printing. Further, the controller unit  205  can read a job from the HDD  209  and can transmit the job to an external apparatus via the external I/F  202 . As mentioned above, the controller unit  205  can execute various output processing for the processing target jobs stored in the HDD  209 . In the present exemplary embodiment, the HDD  209  is a mere example and can be replaced by a volatile RAM. The compression/expansion unit  210  can compress and expand image data stored in the RAM  208  and the HDD  209  using an appropriate compression method (e.g., JBIG or JPEG). 
     A disk controller (DKC)  215  of the controller unit  205  can control every access to the HDD  209 . 
     Further, the controller unit  205  can control various operations to be performed by the sheet processing apparatus  200 . The sheet processing apparatus  200  corresponds to the sheet holding apparatuses and the sheet processing apparatuses illustrated in  FIG. 1 . A media management unit  211  is a module that can manage information about the type of each sheet that can be processed by the digital printing machine  102 . The information about the type of each sheet that can be processed by the digital printing machine  102  is stored in the HDD  209 . 
     The computer  101  is a general computer, which is connected to the digital printing machine  102  via the network  100 . The computer  101  can execute various application programs and can transmit print jobs to the digital printing machine  102 . 
     A configuration of the computer (PC)  101  illustrated in  FIG. 1  according to the first exemplary embodiment is described in detail below with reference to a hardware block diagram illustrated in  FIG. 3 . In  FIG. 3 , a CPU  301  can execute various programs, including an operating system (OS), general applications, and bookbinding applications, which are stored in a program ROM of a ROM  303  or loaded into a RAM  302  from a HDD  311 . The ROM  303  further includes a font ROM and a data ROM. The RAM  302  is functionally operable as a main memory or a work area for the CPU  301 . A keyboard controller (KBC)  305  can control various instructions and information input via the keyboard  309  and a pointing device (not illustrated). A display controller  306  can control a display to be performed by a display unit  310 . A disk controller (DKC)  307  can control every access to the HDD  311  that stores a boot program, various applications, font data, and user files. A network controller (NC)  312  is connected to the network  100  to perform control processing to communicate with other devices connected to the network  100 . A bus  304  connects the CPU  301 , the RAM  302 , the ROM  303 , and various controllers to convey data signals and control signals. 
     The operation unit  204  of the digital printing machine  102  according to the first exemplary embodiment is described in detail below with reference to a plan view illustrated in  FIG. 4 . The operation unit  204  includes a key input unit  402  that can receive user operations entered via hard keys. A touch panel unit  401  is a display unit that can receive user operations entered via software keys (displayed keys). The touch panel unit  401  can display an operation screen. The controller unit  205  controls the operation unit  204 . A display unit of the touch panel unit  401  illustrated in  FIG. 4  can display an operation screen under the control of the controller unit  205 . Items to be displayed on the display unit or items that can be operated via the display unit are changeable according to a user operation performed on the above-mentioned screen, or a momentary state of the digital printing machine  102 . For example, if a user operates the touch panel unit  401 , a UI function program described in detail below identifies the operational content input via the touch panel unit  401  and executes processing according to the identified content. 
     Although the operation unit  204  is constituted by the key input unit  402  and the touch panel unit  401 , the configuration of the operation unit  204  can be modified appropriately. For example, the operation unit  204  can be entirely constituted by the touch panel unit  401 . 
     Various programs that can be executed by the digital printing machine  102  are described below. 
     The programs to be executed by the digital printing machine  102  are stored in the HDD  209  and can be read and executed by the CPU  212  of the controller unit  205  provided in the digital printing machine  102 . 
     A Job Definition Format (JDF) function program is a program that causes the controller unit  205  to realize the print function according to an instruction of the external I/F  202 , when the digital printing machine  102  receives a JDF job via the external I/F  202 . 
     A Page Description Language (PDL) function program is a program that causes the controller unit  205  to realize the print function, when the digital printing machine  102  receives PDL data via the external I/F  202 . 
     A User Interface (UI) function program is a control program dedicated to the operation unit  204 . The UI function program can identify the content of an instruction input by a user of the digital printing machine  102  via the operation unit  204 . The UI function program can perform appropriate screen change processing and can instruct the controller unit  205  to perform requested processing. 
     A sheet management program is a program that can realize a management function relating to sheets that can be used by the digital printing machine  102 . The sheet related information that can be managed by the sheet management program is stored in the HDD  209 . In the present exemplary embodiment, the sheet related information managed by the sheet management program is individual data (e.g., sheet size, media type, and remaining amount of sheets) stored for each sheet holding unit. However, the sheet management information is not limited to the above-mentioned examples. For example, the sheet related information managed by the sheet management program can include another data, such as sheet name and sheet grammage. 
     A job hold function program is a program that can be executed by the controller unit  205  when a user of the digital printing machine  102  instructs executing a job hold function via the operation unit  204 . The job hold function can store print target data in the HDD  209  of the digital printing machine  102  until a print instruction is received from the user. Subsequently, the user selects data to be printed. In response to the print instruction, the digital printing machine  102  prints the instructed data. According to the job hold function, the controller unit  205  sequentially instructs each device to perform a predetermined operation according to an appropriate order in such a way as to realize job hold print processing, based on the processing order and processing conditions described by the job hold function program. The devices that can be controlled by the controller unit  205  in this case according to the job hold function include, for example, the printer unit  203 , the sheet processing apparatus  200 , the HDD  209 , the compression/expansion unit  210 , and the RAM  208 . It is feasible to change settings of each stored job and execute the job according to the changed settings. 
     When the computer  101  (i.e., an external device) stores a print job in the digital printing machine  102  that has the above-mentioned job hold function, the computer  101  performs the following processing. Specifically, the computer  101  instructs storing the print job according to the job hold function instead of using a PDL function program or a JDF function program to perform job print processing. A printing application that operates on the computer  101  (i.e., a job entry source) designates whether to instruct print processing using the PDL function program or the JDF function program or instruct print job storing processing using the job hold function. The above-mentioned designation is reflected to a setting attribute of a target job to be processed by the PDL function program or the JDF function program. The PDL function program or the JDF function program switches the processing based on the setting attribute. 
     A media mismatch determination function program is a function that causes the controller unit  205  to perform the following determination processing when a user of the digital printing machine  102  instructs executing the media mismatch determination function via the operation unit  204 . The media mismatch determination is determination whether attribute information about a sheet to be used in a print job is not registered to any one of the sheet holding units and whether the remaining amount of the sheets to be used in a print job is zero. The controller unit  205  reads attribute information about a sheet that can be used in the digital printing machine  102 , which is stored in the HDD  209  of the digital printing machine  102  by the sheet management program. Then, it is determined whether the attribute information about the sheet to be used in the print job is not registered to any one of the sheet holding units by comparing the read attribute information with attribute information about a sheet to be used in the job held by the job hold function program. Further, the controller unit  205  detects the remaining amount of sheets based on a signal received from the sensor equipped in the sheet holding unit. The controller unit  205  determines whether the remaining amount of the sheets to be used in the print job is zero. A flag that indicates a result of the media mismatch determination performed by the above-mentioned media mismatch determination function program is stored in the RAM  208 . 
     The attribute information about the sheet to be used in the print job includes at least one of a sheet size, a sheet grammage, a sheet surface property, a sheet shape, and a sheet color. 
     Although the function programs have been partly described in detail, it is unnecessary for the system configuration to have all of the functions. A configuration that includes a part of the function programs or other function programs is employable. 
     The data structure of a job, print queue data, and hold queue data of the digital printing machine  102  according to the first exemplary embodiment is described in detail below with reference to  FIGS. 5A to 5C . 
     First, the data structure of a job is described in detail below with reference to  FIG. 5A . The job, when it is entered in the digital printing machine  102 , has the structure of an entry  511  illustrated in  FIG. 5A . The number of entries  511  is equal to the number of jobs that are input and processed by the digital printing machine  102 . The entry  511  is constituted by a job ID  511   a , a print attribute  511   b , and print data  511   c . The job ID  511   a  included in the entry  511  is a unique ID, which can be used to identify and specify each job in the digital printing machine  102 . The print attribute  511   b  in the entry  511  stores print attribute information defined for the job. For example, the print attribute includes a job entry user name, a sheet size, a media type, and a number of pages. Further, the print data  511   c  included in the entry  511  stores print data that describes an image to be drawn on a printing paper. 
     Next, the data structure of print queue data is described in detail below with reference to  FIG. 5B . When a job is input to the print queue, a print queue buffer  521  manages the input job. If a new job is input in a state where no job is present in the print queue, the input job is registered to a queue  1  of the print queue buffer  521 . The next job, if it is input, is registered to a queue  2 . The job stacking operation is performed in this manner. The job stacked in the queue  1  is first subjected to print processing and the jobs stacked in the following queues are sequentially subjected to the print processing. If the print processing of a target job completes, the processed job is deleted from the print queue buffer  521 . Therefore, the order of each job remaining in the print queue buffer  521  is renumbered. Then, the job being currently stacked in the queue  1  is subjected to the print processing. Although  FIG. 5B  illustrates only five queues, the number of queues to be provided in the print queue buffer  521  can be set to an appropriate number considering the capability (e.g., memory capacity and print processing speed) of the digital printing machine  102 . 
     A print queue job attribute table is usable to manage the job attribute to be registered to each print queue. For example, as illustrated in  FIG. 5B , a print queue job attribute table  522  corresponding to one job is registered to the queue  1  and a print queue job attribute table  523  corresponding to another job is registered to the queue  5 . The number of the print queue job attribute tables is equal to the number of queues actually provided in the print queue buffer  521 . Hereinafter, the print queue job attribute table  522  is described in detail below. 
     The print queue job attribute table  522  includes job ID  522   a  as ID information that can identify each job, flag  522   b  that can identify a media mismatch determination result, and flag  522   c  that can identify a suspended processing target. 
     The media mismatch determination is described in detail below with reference to  FIG. 7 . The job substance is not present in the above-mentioned print queue job attribute table  522 . The following description of the present exemplary embodiment is based on the premise that the job substance is not present in the print queue job attribute table  522 . However, the substance of a copied job can be present in the print queue job attribute table  522 . The printing system searches a plurality of entries  511  with reference to a value of the above-mentioned job ID  522   a  to find a job that has the same job ID  522   a . Then, the printing system acquires the print attribute  511   b  and the print data  511   c  from the corresponding entry  511 . 
     Next, the data structure of hold queue data is described in detail below with reference to  FIG. 5C . If a print execution instruction is given for print data managed by a hold queue buffer  531 , the print data moves to the print queue buffer  521 . If a job is input to a hold queue, the job is managed by the hold queue buffer  531 . The hold queue buffer  531  is a storage area of a storage job that can be managed by the job hold function program. The hold queue buffer  531  stores the storage target job, if it is received from an external apparatus, together with print settings. A structure of the hold queue buffer  531  is similar to that of the print queue buffer  521 . Therefore, redundant description thereof will be avoided. 
     A hold queue job attribute table is usable to manage job attribute to be registered to each hold queue. As illustrated in  FIG. 5C , a hold queue job attribute table  532  corresponding to one job is registered to the queue  1  and a hold queue job attribute table  533  corresponding to another job is registered to the queue  5 . The number of the hold queue job attribute tables is equal to the number of queues actually provided in the hold queue buffer  531 . Hereinafter, the hold queue job attribute table  532  is described in detail below. 
     The hold queue job attribute table  532  includes a job ID  532   a  as ID information that can identify each job and a flag  532   b  that can identify a media mismatch determination result. The job substance is not present in the above-mentioned hold queue job attribute table  532 . The following description of the present exemplary embodiment is based on the premise that the job substance is not present in the hold queue job attribute table  532 . However, the substance of a copied job can be present in the hold queue job attribute table  532 . The printing system searches a plurality of entries  511  with reference to a value of the above-mentioned job ID  532   a  to find a job that has the same job ID  532   a . Then, the printing system acquires the print attribute  511   b  and the print data  511   c  from the corresponding entry  511 . 
     The printing system performs the following processing to stack a job in the print queue buffer  521  or the hold queue buffer  531  in response to an entry of the job. To attain the above-mentioned processing, the CPU  212  of the controller unit  205  executes the job hold function program that is read out of the ROM  207  or the HDD  209  and loaded into the RAM  208 . 
     First, a user inputs a job to cause the digital printing machine  102  to perform print processing. Then, a queue designation value indicating the storing destination of the job, which is the print queue buffer  521  or the hold queue buffer  531 , is registered as job attribute. After the job entered by the user is received, the printing system generates a unique ID and allocates the generated unique ID to the input job. Then, the printing system generates one entry  511  for each job. The printing system inputs the generated job ID to the job ID  511   a  field of the entry  511 . The printing system inputs the print attribute of the received job to the print attribute  511   b  field of the entry  511 . The printing system inputs the received print data to the print data  511   c  field of the entry  511 . 
     Next, the above-mentioned queue designation value is read. If the queue designation value is a print queue, the input job is stacked in a queue of the print queue buffer  521 . On the other hand, if the queue designation value is a hold queue, the input job is stacked in a queue of the hold queue buffer  531 . 
     When the input job is stacked in a queue of the print queue buffer  521 , the printing system generates one print queue job attribute table  522  (see  FIG. 5B ) for the input job. Then, the printing system registers the job ID to the job ID  522   a  field of the print queue job attribute table  522 . 
     On the other hand, when the input job is stacked in a queue of the hold queue buffer  531 , the printing system generates one hold queue job attribute table  532  (see  FIG. 5C ) for the input job. Then, the printing system registers the job ID to the job ID  532   a  field of the hold queue job attribute table  532 . 
     An operation that can be performed by the printing system having the above-mentioned configuration according to the present exemplary embodiment is described below. 
     The printing system starts media mismatch determination processing in a state where a screen illustrated in  FIG. 14A  is displayed on a display unit of the operation unit  204 . 
     An example of the job hold function operation screen that can be displayed on the operation unit  204  of the digital printing machine  102  according to the first exemplary embodiment is described in detail below with reference to  FIG. 14A . The job hold function operation screen includes a plurality of display areas and a plurality of operation buttons. Hereinafter, important features in describing the first exemplary embodiment are described in detail below. The job hold function is a function of storing print target data in the HDD  209  of the digital printing machine  102  until a user inputs a print instruction, and subsequently of performing printing based on data corresponding to the print instruction received from the user. The job hold function enables the digital printing machine  102  to store a plurality of print job data in the HDD  209 . As mentioned above, the job hold function allows each user to select an intended print job from a plurality of print jobs stored in the HDD  209  and to designate the execution order. Therefore, it is feasible to perform printing regardless of the order stored in the HDD  209 . 
     A hold job list  1402  is an area provided to display a list of print jobs stored in the above-mentioned hold queue buffer  531 , in the digital printing machine  102 . According to the example illustrated in  FIG. 14A , six print jobs are displayed. However, the digital printing machine  102  can store many print jobs in the HDD  209  although the number of print jobs that can be simultaneously displayed on the hold job list  1402  is limited. For example, when the number of print jobs stored in the HDD  209  is seven or more, a user can touch or press a scroll button  1408  or  1409  to sequentially display all of the stored print jobs on the hold job list  1402 . The hold job list  1402  includes a plurality of fields of job name  1404 , user name  1405 , and date/time  1406  to express each print job. The information stored in the date/time  1406  field indicates storage date and time of the print job stored in the digital printing machine  102 . 
     A user who operates the above-mentioned job hold screen can identify a user&#39;s own job by checking the user name (i.e., operator name)  1405  and can select a target print job. 
     If a user presses or touches the hold job list  1402  with a finger to point a print job portion displayed thereon, the pointed print job turns into selected state. More specifically, the pointed print job is designated as a print target. 
     A screen illustrated in  FIG. 14B  is an example that can be displayed immediately after an operator A operates the job hold function operation screen displayed on the operation unit  204  to select a print job. According to the example illustrated in  FIG. 14B , the operator A successively selects Job A, Job D, and Job E and therefore each of three jobs is in selected state. More specifically, each of selection marks ( 1421 ,  1422 , and  1423 ) indicates the selected state of a corresponding job if it is displayed on the left side of the job name field. Further, a numerical value indicating the selection order is suffixed to each selection mark. Further, a lastly selected Job E  1424  is displayed reversely to indicate that the Job E is currently selected on the hold job list  1402 . 
     A print job list  1403  is an area provided to display print jobs that the digital printing machine  102  has already started their print processing or print jobs that are in a standby state before the digital printing machine  102  starts their print processing. Further, the print job list  1403  is an area provided to display a list of print jobs stored in the above-mentioned print queue buffer  521 . A waiting time  1414  indicates an approximate waiting time required to start the print processing for a print job stored in the print queue buffer  521 . 
     According to the example illustrated in  FIG. 14B , a print job being currently in print processing state is a Job X (status: printing). On the other hand, a print job being in print processing standby state is a Job Y (status: waiting). 
     A details button  1411  is a button that is operable to display a screen that enables a user to confirm details about a print job being in selected state on the hold job list  1402 . According to the example illustrated in  FIG. 14B , if the details button  1411  is pressed in a state where the Job E is lastly selected, detailed information about the Job E can be confirmed. 
     A print start button  1412  is a button that is operable to instruct to start print processing of a print job selected on the hold job list  1402 . If the print start button  1412  is pressed in a state where a target print job is selected from a plurality of print jobs displayed on the hold job list  1402 , the selected print job is displayed on the print job list  1403  and brought into print processing standby state. A stop button  1413  is a button that is operable to stop the execution of the print job being in the state where the print processing has been started by the print start button  1412 . 
     A media mismatch determination button  1407  is a button that is operable to perform media mismatch determination processing on a print job selected from the hold job list  1402 . The media mismatch determination button  1407  can be brought into a gray-out state (i.e., a non-selectable state) if there is not any print job selected on the hold job list  1402 . According to the example illustrated in  FIG. 14B , the printing system performs the media mismatch determination processing for each job being selected state (i.e., Job A, Job D, and Job E). 
     Hereinafter, sequential processing relating to the media mismatch determination according to the first exemplary embodiment, which can be performed for a job stacked in the hold queue buffer  531 , is described in detail below with reference to a flowchart illustrated in  FIG. 6 . To attain the above-mentioned processing, the CPU  212  of the controller unit  205  executes the UI function program that is read out of the ROM  207  or the HDD  209  and loaded into the RAM  208 . The CPU  212  starts the processing of the flowchart illustrated in  FIG. 6  in a state where the hold job list  1402  is displayed on the operation unit  204  and a target job is already selected from jobs stacked in the hold queue buffer  531 . 
     In step S 601 , the CPU  212  waits for an operation that may be performed by a user on the screen illustrated in  FIG. 14A , which can be displayed on the operation unit  204 . The CPU  212  repeats the processing in step S 601  until any operation is performed by the user. If a user operation on the operation unit  204  is detected (YES in step S 601 ), the operation proceeds to step S 602 . 
     In step S 602 , the CPU  212  determines whether the user has pressed the media mismatch determination button  1407 . If it is determined that the media mismatch determination button  1407  has been pressed (YES in step S 602 ), the operation proceeds to step S 700 . In this case, it is useful to bring the media mismatch determination button  1407  into a gray-out state if no print job is selected, so that the user cannot press the media mismatch determination button  1407 . Further, in a case where the CPU  212  performs the media mismatch determination processing only for the selected print job, it is useful that the operation does not proceed to step S 700  even when the media mismatch determination button  1407  is pressed if there is not any selected print job. On the other hand, it is useful that the CPU  212  performs the media mismatch determination processing for all jobs stacked in the hold queue buffer  531  in response to the pressing of the media mismatch determination button  1407 . 
     In step S 700 , the CPU  212  performs media mismatch determination processing. The media mismatch determination processing to be performed in step S 700  is described in detail below with reference to  FIG. 7 . 
     After the CPU  212  completes the media mismatch determination processing in step S 700 , the operation proceeds to step S 1000 . In step S 1000 , the CPU  212  performs media mismatch determination result notification processing. The media mismatch determination result notification processing to be performed in step S 1000  is described in detail below with reference to  FIG. 10 . 
     If the CPU  212  completes the execution of the media mismatch determination result notification processing in step S 1000 , the operation returns to step S 601 . 
     On the other hand, if it is determined that the media mismatch determination button  1407  has not been pressed (NO in step S 602 ), the operation proceeds to step S 603 . 
     In step S 603 , the CPU  212  determines whether the user has pressed a sheet setting button  1410  illustrated in  FIG. 14B . In a state where no job is selected, the sheet setting button  1410  is brought into a gray-out state and therefore the user cannot press the sheet setting button  1410 . Further, in a case where no media mismatch (sheet type inconsistency) occurs in a job, it is useful that the sheet setting button  1410  is brought into a gray-out state even if there is a selected job, to prevent the sheet setting button  1410  from being pressed. More specifically, if the sheet type inconsistent state does not occur even when the remaining amount zero state occurs in the job, it is useful that the sheet setting button  1410  is brought into a gray-out state to prevent the sheet setting button  1410  from being pressed. 
     If it is determined that the sheet setting button  1410  has been pressed (YES in step S 603 ), the operation proceeds to step S 1100 . In this case, it is useful that the operation does not proceed to step S 1100  even when the sheet setting button  1410  is pressed if there is not any selected print job. 
     In step S 1100 , the CPU  212  performs processing relating to settings of a sheet to be used in the selected job. The sheet setting processing to be performed in step S 1100  is described in detail below with reference to  FIG. 11 . If the CPU  212  completes the execution of the sheet setting processing in step S 1100 , the operation returns to step S 601 . Alternatively, it is useful that the operation proceeds to step S 700  after the CPU  212  completes the sheet setting processing in step S 1100 , instead of returning to step S 601 , in such a way as to perform the media mismatch determination processing by replacing the sheet to be used in the job by the sheet having been set in step S 1100 . 
     On the other hand, If it is determined that the sheet setting button  1410  has not been pressed (NO in step S 603 ), the operation proceeds to step S 604 . In step S 604 , the CPU  212  determines whether the user has pressed the print start button  1412 . 
     If it is determined that the print start button  1412  has been pressed (YES in step S 604 ), the operation proceeds to step S 605 . In a state where no job is selected, the print start button  1412  is brought into a gray-out state and therefore the user cannot press the print start button  1412 . 
     In step S 605 , the CPU  212  registers the job selected from the hold job list  1402  illustrated in  FIG. 14B  and instructed to perform print processing, to the print queue buffer  521 . In this case, the job registered to the print queue buffer  521  can be displayed on the print job list  1403  illustrated in  FIG. 14B  and brought into print processing standby state. After the CPU  212  completes the job registration to the print queue buffer  521  (i.e., the processing in step S 605 ), the operation returns to step S 601 . 
     On the other hand, If it is determined that the print start button  1412  has not been pressed (NO in step S 604 ), the operation proceeds to step S 606 . In step S 606 , the CPU  212  performs processing other than the media mismatch determination processing, if it is instructed by a user operation. For example, the processing to be performed in step S 606  includes selecting a job that has been once subjected to the media mismatch determination processing and pressing the details button  1411  illustrated in  FIG. 14B  to display a screen that calls details of a job being in selected state. 
       FIG. 7  is a flowchart illustrating details of the media mismatch determination processing to be performed in step S 700  (see  FIG. 6 ) according to the first exemplary embodiment. To attain the processing illustrated in  FIG. 7 , the CPU  212  of the controller unit  205  executes the media mismatch determination function program that is read out of the ROM  207  or the HDD  209  and loaded into the RAM  208 . The media mismatch determination processing to be performed in step S 700  according to the first exemplary embodiment can be started when the media mismatch determination button  1407  is pressed. Further, if the media mismatch determination button  1407  is pressed again, the CPU  212  performs the media mismatch determination processing again. The determination result can be updated. 
     In the first exemplary embodiment, the CPU  212  performs the following processing for a target print job that the user has selected from the print jobs displayed on the hold job list  1402 . The target print job is not limited to the one having been selected by the user. The target in the above-mentioned processing can be each of the print jobs stacked in the hold queue buffer  531 . 
     First, in step S 701 , the CPU  212  determines whether the number of target print jobs to be subjected to the media mismatch determination processing is equal to or greater than 1. If the determination result in step S 701  indicates that the number of target print jobs to be subjected to the media mismatch determination is equal to or greater than 1 (YES in step S 701 ), the operation proceeds to step S 702 . On the other hand, if the determination result in step S 701  indicates that the number of target print jobs to be subjected to the media mismatch determination is smaller than 1 (NO in step S 701 ), the CPU  212  terminates the media mismatch determination related processing (i.e., the processing in step S 700 ) illustrated in  FIG. 7 . The operation proceeds to step S 1000  illustrated in  FIG. 6 . 
     Then, in step S 702 , the CPU  212  determines whether the media mismatch determination processing has been completed for all print jobs to be subjected to the media mismatch determination processing. If it is determined that the media mismatch determination processing is not yet completed for all target print jobs to be subjected to the media mismatch determination processing (NO in step S 702 ), the operation proceeds to step S 703 . On the other hand, if it is determined that the media mismatch determination processing has been completed for all target print jobs to be subjected to the media mismatch determination processing (YES in step S 702 ), the CPU  212  terminates the media mismatch determination related processing (i.e., the processing in step S 700 ). The operation proceeds to step S 1000  illustrated in  FIG. 6 . 
     In step S 703 , the CPU  212  designates one target print job to be subjected to the media mismatch determination processing. Then, the operation proceeds to step S 704 . In step S 704 , the CPU  212  acquires information indicating a determination method (i.e., sheet type designation or sheet holding unit designation) for determining a sheet holding unit to be used in the print job that has been determined as a target to be subjected to the media mismatch determination processing in step S 703 . Then, the operation proceeds to step S 705 . 
     In step S 705 , the CPU  212  determines whether the method for determining the sheet holding unit to be used in the print job is “sheet type designation” or “sheet holding unit designation”. If the print job is a sheet type designation (YES in step S 705 ), the CPU  212  instructs the media management unit  211  to refer to a sheet management table illustrated in  FIG. 17A . 
     An example of the sheet management table that manages information about sheets stored in each sheet holding unit of the digital printing machine  102  is described in detail below with reference to  FIG. 17A . The sheet management table is stored in the HDD  209  and can be referred to by the CPU  212 . The example of the sheet management table illustrated in  FIG. 17A  includes sheet holding unit ID  1711  that serves as a key to manage information about size  1712 , media type  1713 , and remaining amount  1714  for each of ten sheet holding units provided in the digital printing machine  102 . The remaining amount of sheets can be detected by the sensor equipped in each sheet holding unit. 
     For example, a record  1701  indicates that the sheet stored in a sheet holding unit (ID=1) is A4 in the sheet size, plain paper 1 in the media type, and 3 in the remaining amount. Numerical values indicated by the above-mentioned remaining amount  1714  have the following meanings with respect to the remaining amount; 3: full (100%), 2: small (25%), 1: extremely small (less than 5%), 0: zero (0%), respectively. The accuracy in the above-mentioned sheet remaining amount detection can be increased by improving the performance of the remaining amount sensor. However, the digital printing machine  102  according to the first exemplary embodiment performs the remaining amount detection with reference to the numerical values indicated by the above-mentioned remaining amount. For example, if the storage capacity of a sheet holding unit is 3000 sheets, the remaining amount=full (100%) means that the number of sheets remaining in the sheet holding unit is 3000. The remaining amount=small (25%) means that 750 sheets remain in the sheet holding unit having the storage capacity of 3000 sheets. The remaining amount=extremely small (less than 5%) means that the number of sheets remaining in the sheet holding unit having the storage capacity of 3000 sheets is less than 150. The remaining amount zero (0%) means that there is not any sheet remaining in the sheet holding unit having the storage capacity of 3000 sheets. As mentioned above, it is feasible to detect the remaining amount of sheets stored in each sheet holding unit, at three stages, using the sensor provided in each sheet holding unit. 
     For example, when the print job uses an A4 colored paper (red), the CPU  212  determines whether the A4 colored paper (red) is registered to any one of the sheet holding units, with reference to the sheet management table illustrated in  FIG. 17A . Then, based on a determination result that the sheet size stored in a sheet holding unit (ID=2) is A4 and the media type is colored paper (red), the CPU  212  determines that the sheet holding destination is the sheet holding unit (ID=2). On the other hand, when the print job designates a sheet holding unit (ID=3), the sheet management table illustrated in  FIG. 17A  is referred to and the “A3 plain paper 1” stored in the sheet holding unit (ID=3) is supplied. 
     If the determination result in step S 705  indicates that the target print job is a sheet type designated job (YES in step S 705 ), the operation proceeds to step S 800 . On the other hand, if it is determined that the target print job is a sheet holding unit designated job (NO in step S 705 ), the operation proceeds to step S 900 . The processing to be performed in step S 800  and the processing to be performed in step S 900  are described in detail below with reference to  FIGS. 8 and 9 . If the CPU  212  completes the processing in step S 800  or step S 900 , the operation returns to step S 702 . 
       FIG. 8  is a flowchart illustrating the media mismatch determination processing to be performed in step S 800  illustrated in  FIG. 7  when the target print job to be subjected to the media mismatch determination processing is a sheet type designated job. To attain the processing illustrated in  FIG. 8 , the CPU  212  of the controller unit  205  executes the media mismatch determination function program that can be read out of the ROM  207  or the HDD  209  and loaded into the RAM  208 . 
     In step S 801 , the CPU  212  acquires information about the sheet type and the remaining amount of sheets set in each sheet holding unit provided in the digital printing machine  102 . The CPU  212  instructs the media management unit  211  to perform the processing in step S 801 , for example, with reference to the above-mentioned sheet management table illustrated in  FIG. 17A . Then, the operation proceeds to step S 802 . In step S 802 , the CPU  212  reads a print job stored in the hold queue buffer  531 , with reference to the target print job to be subjected to the media mismatch determination processing. Then, the CPU  212  acquires the number of sheet types being sheet type designated, of sheet types to be used in the print jobs illustrated in  FIG. 17B . 
       FIG. 17B  illustrates information about sheets to be used in Job A, Job D, and Job E illustrated in  FIG. 14B . The information illustrated in  FIG. 17B  can be stored when the job hold function program stores a print job in the hold queue buffer  531  because print settings can be simultaneously stored. The print settings include sheet information about each print job.  FIG. 17B  indicates that the Job A uses two types of sheets, in which one sheet is A4 in the sheet size and “plain paper 1” in the media type and the other sheet is A4 in the sheet size and “two-sided coated paper 1” in the media type. Further,  FIG. 17B  indicates that the Job D uses two types of sheets, in which one sheet is LTR in the sheet size and “plain paper 1” in the media type and the other sheet is 11×17 in the sheet size and “plain paper 1” in the media type. Similarly,  FIG. 17B  indicates that the Job E uses three types of sheets, in which the first sheet is A4 in the sheet size and “plain paper 1” in the media type, the second sheet is A4 in the sheet size and “colored paper (red)” in the media type, and the third sheet is A3 in the sheet size and “two-sided coated paper 2” in the media type. Each combination of the sheet size and the media type defines a sheet type. 
     Next, the operation proceeds to step S 803 . The CPU  212  sets two types of flags (i.e., Flag A and Flag B) each holding a result in the media mismatch determination processing, for each sheet type acquired in step S 802 , and performs initialization processing for respective flags. In this case, the Flag A is a flag that holds a determination result as to whether attribute information about a sheet to be used in the print job is not registered to any one of the sheet holding units. The Flag A is stored in the RAM  208 . On the other hand, the Flag B is a flag that holds a determination result as to whether the remaining amount of sheets to be used in the print job is zero. The Flag B is stored in the RAM  208 . The Flag A having a “true” value indicates a media mismatch (i.e., sheet type inconsistent) state. More specifically, when the Flag A is “true”, it means that a sheet type designated by the print job is not set in any one of the sheet holding units. On the other hand, the Flag B having a “true” value indicates a media mismatch (sheet remaining amount zero) state. More specifically, when the Flag B is “true”, it means that the remaining amount of sheets having a sheet type to be used in a print job is zero. In the initialization processing, the Flag A is initialized to have a value of true (mismatch) and the Flag B is initialized to have a value of true (remaining amount zero). 
     Next, the operation proceeds to step S 804 . The CPU  212  determines whether the above-mentioned media mismatch determination processing has been completed for all sheet types of the target print job to be subjected to the media mismatch determination processing. If the media mismatch determination processing is not yet completed for all sheet types (NO in step S 804 ), the operation proceeds to step S 805 . In step S 805 , the CPU  212  selects one target sheet type to be subjected to the media mismatch determination processing in the print job. Then, the operation proceeds to step S 806 . 
     In step S 806 , the CPU  212  determines whether the media mismatch determination processing has been completed for all sheet holding units provided in the digital printing machine  102 . If it is determined that there is at least one sheet holding unit that is not yet subjected to the media mismatch determination processing (NO in step S 806 ), the operation proceeds to step S 807 . In step S 807 , the CPU  212  designates a target sheet holding unit to be next subjected to the media mismatch determination. Then, the operation proceeds to step S 808 . 
     In step S 808 , the CPU  212  determines whether the target sheet type to be subjected to the media mismatch determination processing determined in step S 805  coincides with a sheet type being set and registered to the target sheet holding unit to be subjected to the media mismatch determination processing determined in step S 807 . If it is determined that the compared sheet types coincide with each other (YES in step S 808 ), the operation proceeds to step S 809 . On the other hand, if it is determined that the compared sheet types does not coincide with each other (NO in step S 808 ), the operation returns to step S 806  to repeat the processing in step S 806  and subsequent steps. 
     In step S 809 , the CPU  212  stores the value of Flag A as being “false (match)” indicating that the print job designates the sheet type registered to the sheet holding unit, in association with the print job. Then, the operation proceeds to step S 810 . The CPU  212  determines whether the remaining amount of sheets in the target sheet holding unit to be subjected to the media mismatch determination processing determined in step S 807  is not zero. If it is determined that the remaining amount of sheets is not zero (YES in step S 810 ), the operation proceeds to step S 811 . In step S 811 , the CPU  212  stores the value of Flag B as being “false (remaining amount is not zero)” indicating that the remaining amount of sheets having the sheet type to be used in the print job is not zero, in association with the print job. Then, the operation returns to step S 806  to repeat the processing in step S 806  and subsequent steps. On the other hand, if t it is determined that the remaining amount of sheets is zero (NO in step S 810 ), the operation returns to step S 806  to repeat the processing in step S 806  and subsequent steps. 
     If the determination result in step S 806  indicates that the media mismatch determination processing has been completed for all sheet holding units (YES in step S 806 ), the operation returns to step S 804  to repeat the processing in step S 804  and subsequent steps. Further, if the determination result in step S 804  indicates that the media mismatch determination has been completed for all sheet types of the target print job to be subjected to the media mismatch determination processing, the CPU  212  terminates the media mismatch determination processing (i.e., the processing to be performed in step S 800  when the target print job is a sheet type designated job). Subsequently, the operation returns to step S 702  illustrated in  FIG. 7 . As mentioned above, the CPU  212  performs the media mismatch determination processing in step S 800  illustrated in  FIG. 7  if the target print job is a sheet type designated job. 
     On the other hand, if the determination result in step S 705  illustrated in  FIG. 7  indicates that the target print job is a sheet holding unit designated job (NO in step S 705 ), the operation proceeds to step S 900 .  FIG. 9  is a flowchart illustrating the media mismatch determination processing that can be performed by the CPU  212  in step S 900  illustrated in  FIG. 7  when the target print job to be subjected to the media mismatch determination processing is the sheet holding unit designated job. To attain the processing illustrated in  FIG. 9 , the CPU  212  of the controller unit  205  executes the media mismatch determination function program that is read out of the ROM  207  or the HDD  209  and loaded into the RAM  208 . 
     In step S 901 , the CPU  212  acquires the number of sheet types whose sheet holding units are designated and used in the print job, as information about sheets used in the print jobs illustrated in  FIG. 17B , with respect to the target print job to be subjected to the media mismatch determination processing. Next, the operation proceeds to step S 902 . The CPU  212  sets a flag (Flag) that holds a result of the media mismatch determination (i.e., sheet remaining amount determination) processing for each sheet type acquired in step S 901  and performs initialization processing for the flag being set. 
     The Flag being set in step S 902  is a flag that holds a determination result as to whether the remaining amount of sheets to be used in the print job is not zero. The value of Flag is stored in the RAM  208 . The Flag having a value “true (remaining amount is zero)” indicates a media mismatch state. More specifically, when the Flag is “true (remaining amount is zero)”, it means that the remaining amount of sheets having a sheet type to be used in the print job is zero. In the initialization processing, the Flag is initialized to have the value “true (remaining amount is zero)”. However, when the target print job is a sheet holding unit designated job, the CPU  212  does not determine whether a sheet to be used in the job is registered to a sheet holding unit designated by the job. Therefore, a sheet type inconsistency determination flag is not used. 
     Next, the operation proceeds to step S 903 . The CPU  212  determines whether the above-mentioned media mismatch determination (i.e., sheet remaining amount determination) processing has been completed for all sheet types of a target print job to be subjected to the media mismatch determination (i.e., sheet remaining amount determination) processing. If it is determined that the media mismatch determination processing is not yet completed for all sheet types (NO in step S 903 ), the operation proceeds to step S 904 . In step S 904 , the CPU  212  selects one target sheet type to be subjected to the media mismatch determination (sheet remaining amount determination) in the print job. Then, the operation proceeds to step S 905 . In step S 905 , the CPU  212  acquires information about the remaining amount of sheets in the sheet holding unit designated by the target sheet type to be subjected to the sheet remaining amount determination processing, which has been determined in step S 904 , and used in the print job. The CPU  212  instructs the media management unit  211  to perform the above-mentioned processing in step S 905 , for example, with reference to the sheet management table illustrated in  FIG. 17A . 
     The operation proceeds to step S 906 . The CPU  212  determines whether the remaining amount of sheets in the sheet holding unit acquired in step S 905  is zero. If it is determined that the remaining amount of sheets is not zero (NO in step S 906 ), the operation proceeds to step S 907 . In step S 907 , the CPU  212  stores the value of Flag as being “false (remaining amount is not zero)” indicating that the remaining amount of sheets to be used in the print job is not zero, in association with the print job. Then, the operation returns to step S 903  to repeat the processing in step S 903  and subsequent steps. 
     On the other hand, if it is determined that the remaining amount of sheets is zero (YES in step S 906 ), the operation returns to step S 903  to repeat the processing in step S 903  and subsequent steps. 
     Further, if the determination result in step S 903  indicates that the media mismatch determination has been completed for all sheet types of the target print job to be subjected to the media mismatch determination processing (YES in step S 903 ), the CPU  212  terminates the media mismatch determination processing (i.e., the processing to be performed in step S 900  when the target print job is a sheet holding unit designated job). Subsequently, the operation returns to step S 702  illustrated in  FIG. 7 . 
     As mentioned above, the CPU  212  performs the media mismatch determination processing in step S 900  illustrated in  FIG. 7  if the target print job is a sheet holding unit designated job. 
       FIG. 10  is a flowchart illustrating the processing to be performed in step S 1000  (i.e., the processing to notify a media mismatch determination result to the hold job list  1402 ). To attain the processing illustrated in  FIG. 10 , the CPU  212  of the controller unit  205  executes the UI function program that is read out of the ROM  207  or the HDD  209  and loaded into the RAM  208 . 
     In step S 1001 , the CPU  212  determines whether the print job having been subjected to the media mismatch determination processing is currently displayed on the hold job list  1402 . If it is determined that the print job having been subjected to the media mismatch determination processing is currently displayed on the hold job list  1402  (YES in step S 1001 ), the operation proceeds to step S 1002 . 
     In step S 1002 , the CPU  212  reads the value of Flag A, which is the sheet type inconsistency flag that holds a determination result as to whether attribute information about sheets to be used in the print job having been subjected to the media mismatch determination processing is not registered to any one of the sheet holding units, from the RAM  208 . Then, the CPU  212  determines whether the value of Flag A is “false (match)”. 
     If it is determined that the value of Flag A is true (mismatch) in at least one sheet type, it indicates a media mismatch (sheet type inconsistent) state. More specifically, when the Flag A is true (mismatch), it means that a sheet type designated by the print job is not set in any one of the sheet holding units. Accordingly, in this case (NO in step S 1002 ), the operation proceeds to step S 1003 . For example, as illustrated in  FIG. 14C , the CPU  212  displays an inconsistency mark  1431  indicating the media mismatch state in the entry of a print job on the hold job list  1402  in association with the print job. The inconsistency mark  1431  indicates that the sheet having the sheet type (e.g., size and media type) to be used in the print job is not set in any one of the sheet holding units. Then, the CPU  212  terminates the sequential media mismatch determination result notification processing (i.e., the processing in step S 1000 ). Then, the operation returns to step S 601  illustrated in  FIG. 6 . 
     On the other hand, if it is determined that the value of Flag A is false in all types of jobs having been subjected to media mismatch determination processing (YES in step S 1002 ), the operation proceeds to step S 1004 . In step S 1004 , the CPU  212  reads the value of Flag B from the RAM  208  and determines whether the value of Flag B is “false (remaining amount is not zero)”. The Flag B is a flag that holds a sheet remaining amount determination result as to whether the remaining amount of sheets to be used in the print job having been subjected to the media mismatch determination processing is zero. 
     If the determination result in step S 1004  indicates that the value of Flag B is “true (remaining amount is zero)” in at least one sheet type, it indicates the media mismatch (i.e. remaining amount is zero) state. More specifically, the CPU  212  determines that the remaining amount of sheets having the sheet type to be used in the print job is zero. Accordingly, in this case (No in step S 1005 ), the operation proceeds to step S 1005 . For example, as illustrated in  FIG. 14C , the CPU  212  displays a remaining amount zero mark  1432  indicating the media mismatch state in the entry of a print job on the hold job list  1402  in association with the print job. The remaining amount zero mark  1432  indicates that the remaining amount of the sheet to be used in the print job is zero although the sheet is set to the sheet holding unit. Then, the CPU  212  terminates the sequential media mismatch determination result notification processing (i.e., the processing in step S 1000 ). Then, the operation returns to step S 601  illustrated in  FIG. 6 . 
     On the other hand, if it is determined that the value of Flag B is false in all types of jobs having been subjected to media mismatch determination processing (YES in step S 1004 ), it means that the remaining amount of sheets is not zero in all sheet types to be used in the print job. Therefore, the CPU  212  terminates the sequential media mismatch determination result notification processing (i.e., the processing in step S 1000 ). Then, the operation returns to step S 601  illustrated in  FIG. 6 . 
     When the result of the media mismatch determination processing indicates that the sheet type inconsistency occurs in a target job, the printing system displays the inconsistency mark in association with the job to notify the result of the media mismatch determination processing (see step S 1003 ). Further, when the “sheet remaining amount zero” state occurs in a target job, the printing system displays the remaining amount zero mark in association with the job to notify the “sheet remaining amount zero” state (see step S 1005 ). However, the present exemplary embodiment can be modified in the following manner. For example, any other mark (or sound or light) is usable if it can be recognized by a user to confirm the above-mentioned situation that the sheet type inconsistency occurs or the remaining amount of sheets is zero in the currently processed job, before instructing the execution of the job. 
     Subsequently, an example of the operation screen that can be displayed by the digital printing machine  102  according to the first exemplary embodiment, after the media mismatch determination result is notified on the hold job list  1402 , is described with reference to  FIG. 14C . On the other hand, the operation screen illustrated in  FIG. 14B  is an example that can be displayed immediately after the operator A operates the job hold function operation screen displayed on the operation unit  204  to select a print job. Each portion illustrated in  FIG. 14C , if it is similar to that illustrated in  FIG. 14B , is denoted by the same symbol. Similar to  FIG. 14B , according to the example illustrated in  FIG. 14C , the operator A successively selects Job A, Job D, and Job E and therefore each of three jobs is in selected state. 
     In  FIG. 14C , the media mismatch determination is performed for each of the selected three jobs (i.e., Job A, Job D, and Job E) having been selected by the user, to check whether a sheet to be used in each print job matches with the sheet having been set to the sheet holding unit of the digital printing machine  102 . 
     For example, the sheets to be used in the print job “Job A” are set to the sheet holding units as illustrated in  FIGS. 17A and 17B  and the remaining amount of sheets is not zero in each sheet holding unit. Accordingly, none of the inconsistency mark  1431  and the remaining amount zero mark  1432  is displayed for the Job A. In this case, before instructing the start of printing, the user can know that the possibility of causing a media mismatch is extremely low if the user presses the print start button  1412 . 
     Further, the sheets to be used in the print job “Job D” are set to the sheet holding units as illustrated in  FIGS. 17A and 17B . However, the remaining amount of sheets is zero in at least one of the sheet holding units. More specifically, the remaining amount of sheets having the size “11×17” and the media type “plain paper 1” is 0 although the sheets are set to a “sheet holding unit  9 ”. Accordingly, if the user presses the print start button  1412  in the above-mentioned state, the media mismatch (i.e., the sheet remaining amount zero state) occurs at the sheet supply timing of the above-mentioned sheet being “11×17” sized and therefore the print processing stops. Accordingly, a display of the remaining amount zero mark  1432  appears on the right side in the display field of Job D. When the user recognizes the remaining amount zero mark  1432  displayed on the list, the user can perform an appropriate preparatory operation. More specifically, the user can replenish the sheet holding unit  9  with a sufficient amount of sheets having the size “11×17” and the media type “plain paper 1”. 
     Further, at least one of the sheets to be used in the print job “Job E” is not set in any one of the sheet holding units as illustrated in  FIGS. 17A and 17B . More specifically, the sheet being “A3” in the size and “two-sided coated paper 2” in the media type is not set in any one of the sheet holding units. Accordingly, a display of the inconsistency mark  1431  appears on the right side in the display field of Job E. If the user presses the details button  1411  in the state illustrated in  FIG. 14C , the size and media type information ( 1728 ,  1729 , and  1730 ) about the sheets to be used in the selected Job E can be displayed. In this case, the medial information (A3 and two-sided coated paper) that is not set to any one of the sheet holding units is, for example, reversely displayed to notify the user of each sheet being not set in any one of the sheet holding units. Accordingly, before instructing the start of printing, the user can know that the media mismatch (i.e., sheet type inconsistent) state may occur at the sheet feeding timing and the print job may stop if the user presses the print start button  1412  in the above-mentioned state. When the user confirms the inconsistency mark  1431  displayed on the list, the user can perform an appropriate preparatory operation. More specifically, the user can designate another sheet holding unit (preferably, a sheet holding unit that is not determined to use in the print job) and change the settings of the designated sheet holding unit to include A3 in the sheet size and “two-sided coated paper 2” in the media type. More specifically, the user can press the sheet setting button  1410  to designate the sheet holding unit that is not determined to use in the print job and change the sheet settings of the designated sheet holding unit. Further, the user can replenish the designated sheet holding unit with the corresponding sheet. In this case, if there is any sheet remaining in the sheet holding unit, the user can remove all of the remaining sheets. 
     In the present exemplary embodiment, as illustrated in  FIG. 14C , the shape of the inconsistency mark  1431  and the shape of the remaining amount zero mark  1432  are differentiated from each other. Therefore, the user can discriminate and recognize whether the sheet to be used in the job is not set in any one of the sheet holding units or whether the remaining amount is zero although the sheet to be used in the job is set in any one of the sheet holding units. When the media mismatch determination is performed as mentioned above, it becomes possible for the user to prevent the print job from being stopped because the warning mark  1431  or  1432  is displayed in association with the print job that may cause a media mismatch. 
     Further, if the user selects the Job D and presses the details button  1411  in the state illustrated in  FIG. 14C , information about the size and the media type ( 1726  and  1727 ) of sheets to be used in the Job D can be displayed. In this case, the CPU  212  blinks sheet information if the remaining amount of sheets is zero. Further, the CPU  212  blinks a display of the sheet holding unit to which the corresponding sheet is set. Thus, the user can identify the information about sheet size and media type of each sheet to be used in the Job D, if the remaining amount is zero, together with the sheet holding unit that stores the identified sheet. As mentioned above, even in a case where the sheet size and the media type are displayed, the CPU  212  differentiates the way of displaying sheet information when the sheet is not set in any one of the sheet holding units from the way of displaying sheet information when the remaining amount of sheets is zero. Accordingly, the user can discriminate and confirm whether the sheet having the displayed size and type is not set in any one of the sheet holding units or whether the remaining amount of sheets is zero. In this case, the printing system reversely displays the medial information that is not set in any one of the sheet holding units and blinks the displayed information about each sheet if the remaining amount is zero. However, the screen display is not limited to the above-mentioned example. For example, it is feasible to display the sheet information in association with the inconsistency mark  1431  or the remaining amount zero mark  1432 . 
       FIG. 11  is a flowchart illustrating the processing to be performed in step S 1100  illustrated  FIG. 6 , to perform settings for the sheet to be used in the selected print job. To attain the processing illustrated in  FIG. 11 , the CPU  212  of the controller unit  205  executes the UI function program that is read out of the ROM  207  or the HDD  209  and loaded into the RAM  208 . The CPU  212  starts the processing of the flowchart illustrated in  FIG. 1 n    a state where a mismatch sheet list screen  1501  illustrated in  FIG. 15A  is displayed on the operation unit  204  and a mismatch sheet is selected from a sheet list  1502 . 
     The mismatch sheet list screen  1501  is a screen that allows a user to perform mismatch sheet settings for a job in which the media mismatch has occurred. The sheet list  1502  can be created by adding up mismatch sheets of media mismatch (sheet type inconsistency) jobs, of the sheets to be used for respective jobs being in selected state in the hold job list  1402 . According to the example illustrated in  FIG. 15A , the sheet list  1502  displays only the mismatch sheets. However, the sheet list  1502  can be configured to display all sheets to be used in the job being in selected state on the hold job list  1402 . Determining the mismatch sheet of each media mismatch (sheet type inconsistency) job is feasible by referring to the value of the above-mentioned flag (Flag A) that holds the media mismatch determination result being set for each sheet type to be used in the job. 
     According to the example illustrated in  FIG. 15A , information about an “A4 Paper1” sheet and an “A3 thick paper” sheet is displayed on the sheet list  1502 . The user can know that the “A3 thick paper” sheet is in a selected state and the “A4 Paper1” sheet is not in a selected state. Further, the user can know that the “A4 Paper1” sheet is the paper to be used in the job secondly selected on the hold job list  1402  and the “A3 thick paper” sheet is the paper to be used in the job fourthly selected on the hold job list  1402 . 
     Further, the user can know the occurrence of a media mismatch in each sheet type by checking the inconsistency mark  1431  displayed in association with each of the “A3 thick paper” sheet and the “A4 Paper1” sheet. 
     In step S 1101 , the CPU  212  checks if a user instruction is input via the screen illustrated in  FIG. 15A , which can be displayed on the operation unit  204 . The CPU  212  repeats the processing in step S 1101  until a user performs an input operation. If a user instruction is input via the operation unit  204  (YES in step S 101 ), the operation proceeds to step S 1102 . In a state where no sheet is selected, a sheet details button  1503  and a sheet holding unit selection button  1505  (i.e., two buttons illustrated in  FIG. 15A ) are brought into a gray-out state and therefore cannot be pressed. 
     In step S 1102 , the CPU  212  determines whether the user operation is an event to press the sheet holding unit selection button  1505 . If it is determined that the sheet holding unit selection button  1505  has been pressed (YES in step S 1102 ), the operation proceeds to step S 1200 . 
     In step S 1200 , the CPU  212  performs sheet holding unit selection screen display processing. Then, the operation proceeds to step S 1300 . The processing to be performed in step S 1200  is described in detail below with reference to  FIG. 12 . 
     In step S 1300 , the CPU  212  performs sheet holding unit attribute information setting processing. Then, the operation returns to step S 1101 . The processing to be performed in step S 1300  is described in detail below with reference to  FIG. 13 . 
     On the other hand, if it is determined that the sheet holding unit selection button  1505  has not been pressed (NO in step S 1102 ), the operation proceeds to step S 1103 . In step S 1103 , the CPU  212  determines whether the user operation is an event to press a cancel button  1504 . If it is determined that the cancel button  1504  has been pressed (YES in step S 1103 ), the CPU  212  discards the information being set on the mismatch sheet list screen  1501 . Then, the CPU  212  terminates the setting for the sheet to be used in the selected print job (i.e., the processing in step S 1100  illustrated in  FIG. 6 ). Then, the operation returns to step S 601  illustrated in  FIG. 6 . 
     On the other hand, if it is determined that the cancel button  1504  has not been pressed (NO in step S 1103 ), the operation proceeds to step S 1104 . In step S 1104 , the CPU  212  performs other processing according to a user operation (instruction). Then, the operation returns to step S 1101 . For example, the processing to be performed in step S 1104  includes changing the screen to a sheet details information screen  1521  illustrated in  FIG. 15C  in response to a pressing of the sheet details button  1503 . The user can know detailed information about sheet attribute information, such as a sheet name, size, a grammage, a surface property, a feature, a color, and an adjustment of creep (deviation) correction amount, with reference to the sheet details information screen  1521  illustrated in  FIG. 15C . 
       FIG. 12  is a flowchart illustrating the processing to be performed in step S 1200  illustrated in  FIG. 11 , which is the processing to display a screen that enables a user to select a mismatch sheet attribute information settable sheet holding unit. To attain the processing illustrated in  FIG. 12 , the CPU  212  of the controller unit  205  executes the UI function program that is read out of the ROM  207  or the HDD  209  and loaded into the RAM  208 . Each mismatch sheet being in selected state on the sheet list  1502  illustrated in  FIG. 15A  is a target mismatch sheet to be subjected to the processing in step S 1200 . 
     In step S 1201 , the CPU  212  determines whether the determination processing has been completed for all sheet holding units to determine a sheet holding unit to which the mismatch sheet attribute information is settable. If it is determined that the determination processing is not yet completed for all sheet holding units (NO in step S 1201 ), the operation proceeds to step S 1202 . 
     In step S 1202 , the CPU  212  selects a target sheet holding unit to be subjected to mismatch sheet attribute information settability determination processing. Then, the operation proceeds to step S 1203 . 
     In step S 1203 , the CPU  212  acquires attribute information about the sheet set in the target sheet holding unit. More specifically, the CPU  212  can instruct the media management unit  211  to acquire attribute information about the sheet set in the target sheet holding unit with reference to the sheet management table illustrated in  FIG. 17A . 
     Subsequently, the operation proceeds to step S 1204 . The CPU  212  determines whether the mismatch sheet attribute information is settable to the target sheet holding unit determined in step S 1202 . The determination whether specific sheet attribute information is settable to the sheet holding unit depends on the combination of media type and sheet holding unit. For example, the sheet holding unit  1  is smaller in the size of accommodatable papers, compared to other sheet holding units. Therefore, any sheet whose size is greater than A4 cannot be stored in the sheet holding unit  1 . Therefore, A3 sheets cannot be set in the sheet holding unit  1 . Further, for example, a portion that rolls a sheet is provided in a conveyance path extending from the paper feed tray. Therefore, if a sheet has a larger grammage, it is unfeasible for the sheet to pass the above-mentioned rolling portion. The sheet having a large grammage cannot be set in any one of the sheet holding units. 
     As mentioned above, feeding a specific sheet may be restricted if the sheet holding unit is inappropriate in position, sheet size, or sheet grammage. 
     If the determination result in step S 1204  indicates that the mismatch sheet attribute information is settable to the sheet holding unit determined in step S 1202  (YES in step S 1204 ), the operation proceeds to step S 1205 . On the other hand, if it is determined that the mismatch sheet attribute information is not settable to the sheet holding unit determined in step S 1202  (NO in step S 1204 ), the operation proceeds to step S 1208 . 
     In step S 1205 , the CPU  212  determines whether at least one of jobs selected from the hold job list  1402  uses the sheet stored in the target sheet holding unit determined in step S 1202 . If it is determined that there is not any selected job that uses the sheet stored in the target sheet holding unit (NO in step S 1205 ), the operation proceeds to step S 1206 . If it is determined that there is at least one selected job that uses the sheet stored in the target sheet holding unit (YES in step S 1205 ), the operation proceeds to step S 1208 . 
     In step S 1206 , the CPU  212  determines whether at least one of jobs displayed on the print job list  1403  uses the sheet stored the target sheet holding unit determined in step S 1202 . If it is determined that there is not any print queue job that uses the sheet stored in the target sheet holding unit (NO in step S 1206 ), the operation proceeds to step S 1207 . On the other hand, if it is determined that there is at least one print queue job that uses the sheet stored in the target sheet holding unit (YES in step S 1206 ), the operation proceeds to step S 1208 . 
     In step S 1207 , the CPU  212  determines that the mismatch sheet attribute information is settable to the sheet holding unit determined in step S 1202 . Then, the operation returns to step S 1201  to repeat the processing in step S 1201  and subsequent steps. 
     On the other hand, in step S 1208 , the CPU  212  determines that the mismatch sheet attribute information is not settable to the sheet holding unit determined in step S 1202 . Then, the operation returns to step S 1201  to repeat the processing in step S 1201  and subsequent steps. 
     On the other hand, if the determination result in step S 1201  indicates that the determination processing has been completed for all sheet holding units (YES in step S 1201 ), the operation proceeds to step S 1209 . In step S 1209 , the CPU  212  causes the operation unit  204  to display a sheet holding unit selection screen  1511  illustrated in  FIG. 15B  based on the determination result (step S 1207  or step S 1208 ) with respect to the mismatch sheet attribute information settable sheet holding unit. 
     After completing the processing in step S 1209 , the CPU  212  terminates the sequential processing relating to step S 1200  illustrated in  FIG. 11 . Then, the operation proceeds to step S 1300  illustrated in  FIG. 11 . 
       FIG. 18  illustrates a determination result with respect to the mismatch sheet attribute information settable sheet holding unit. According to the example illustrated in  FIG. 18 , attribute information about the sheet to be set (mismatch sheet) is “A3 thick paper”. Further, it is restricted in such a way that the A3 sheet cannot be set to the sheet holding unit  1 . Job H, Job I, Job J, and Job K are target selection jobs (hold jobs) to be sequentially subjected to the determination processing in step S 1205 . The paper to be used in the Job H is “A4 plain paper”. The paper to be used in the Job I is “A4 Paper1”. The paper to be used in the Job J is “A3 plain paper”. The paper to be used in the Job K is “A3 thick paper”. Further, the “A4 Paper1” to be used in the Job I and the “A3 thick paper” to be used in the Job K are not set to any sheet holding unit. In other words, these papers are mismatch sheets. Therefore, the inconsistency mark  1431  is displayed in association with each mismatch sheet. As illustrated in  FIG. 18 , each of the sheet holding unit  2  and the sheet holding unit  3  is determined as the sheet holding unit to which the “A3 thick paper” is settable. 
       FIG. 13  is a flowchart illustrating the processing to be performed in step S 1300  illustrated in  FIG. 11 , which is the sheet holding unit attribute information setting processing. To attain the processing illustrated in  FIG. 13 , the CPU  212  of the controller unit  205  executes the UI function program that is read out of the ROM  207  or the HDD  209  and loaded into the RAM  208 . The CPU  212  starts the processing illustrated in the flowchart in  FIG. 13  in a state where the sheet holding unit selection screen  1511  is displayed on the operation unit  204 . 
     In step S 1301 , the CPU  212  checks if a user instruction is input via the sheet holding unit selection screen  1511  illustrated in  FIG. 15B , which can be displayed on the operation unit  204 . The CPU  212  repeats the processing in step S 1301  until a user performs an input operation. If a user instruction is an input operation via the operation unit  204  (YES in step S 1301 ), the operation proceeds to step S 1302 . In a state where no sheet holding unit is selected, a sheet details button  1512  and an OK button  1514  (i.e., two buttons illustrated in  FIG. 15B ) are brought into a gray-out state and therefore cannot be pressed. Further, if the mismatch sheet attribute information is not settable, the sheet holding unit determined in step S 1200  illustrated in  FIG. 11  is brought into a gray-out state and cannot be selected. According to the example illustrated in  FIG. 15B , each of the sheet holding unit  1 , the sheet holding unit  4 , the sheet holding unit  5 , and the sheet holding unit  6  is the sheet holding unit determined as being unsettable with respect to the A3 thick paper. On the other hand, each of the sheet holding unit  2  and the sheet holding unit  3  is the sheet holding unit determined as being settable with respect to the A3 thick paper. 
     In step S 1302 , the CPU  212  determines whether the user operation is the event to select a sheet holding unit to which the mismatch sheet attribute information is settable. If it is determined that the user operation is the event to select the sheet holding unit to which the mismatch sheet attribute information is settable (YES in step S 1302 ), the operation proceeds to step S 1303 . In step S 1303 , the CPU  212  brings the selected sheet holding unit into selected state. Then, the operation returns to step S 1301 . According to the example illustrated in  FIG. 15B , the user can know that the sheet holding unit being in selected state is the sheet holding unit  2  determined as being settable with respect to the A3 thick paper. 
     On the other hand, if it is determined that the user operation is not the event to select the sheet holding unit to which the mismatch sheet attribute information is settable (NO in step S 1302 ), the operation proceeds to step S 1304 . If it is determined that the user operation is the event to select the sheet holding unit to which the mismatch sheet attribute information is settable (YES in step S 1302 ), the sheet holding unit is brought into selected state in step S 1303  and the operation returns to step S 1301 . Therefore, the CPU  212  performs the processing in step S 1304  and subsequent steps in a state where the sheet holding unit to which the mismatch sheet is settable is already selected. 
     In step S 1304 , the CPU  212  determines whether the user operation is the event to press a cancel button  1513 . If it is determined that the user operation is the event to press the cancel button  1513  (YES in step S 1304 ), the CPU  212  discards the information being set on the sheet holding unit selection screen  1511 . Then, the CPU  212  terminates the sheet holding unit attribute information setting processing (i.e., the processing in step S 1300  illustrated in  FIG. 11 ). Then, the operation returns to step S 1101  illustrated in  FIG. 11 . 
     On the other hand, if it is determined that the user operation is not the event to press the cancel button  1513  (NO in step S 1304 ), the operation proceeds to step S 1305 . In step S 1305 , the CPU  212  determines whether the user operation is the event to press the OK button  1514 . If it is determined that the OK button  1514  has been pressed (YES in step S 1305 ), the operation proceeds to step S 1306 . 
     In step S 1306 , the CPU  212  sets mismatch sheet attribution information about the job in which the media mismatch occurs to the sheet holding unit being brought into the selected state in step S 1303 . According to the example illustrated in  FIG. 15B , the A3 thick paper is set to the sheet holding unit  2  being in selected state. Then, the CPU  212  terminates the sheet holding unit attribute information setting processing (i.e., the processing in step S 1300  illustrated in  FIG. 11 ). Then, the operation returns to step S 1100  illustrated in  FIG. 11 . 
     On the other hand, if it is determined that the OK button  1514  has not been pressed (NO in step S 1305 ), the operation proceeds to step S 1307 . In step S 1307 , the CPU  212  performs other processing if it is instructed by a user operation. Then, the operation returns to step S 1301 . For example, the processing to be performed in step S 1307  includes displaying the sheet details information screen  1521  illustrated in  FIG. 15C  in response to a pressing of the sheet details button  1512 . 
     As described above, the CPU  212  performs the sequential sheet setting processing in step S 1100  illustrated in  FIG. 6 . 
     As described above, to solve the media mismatch (sheet type inconsistent) state, the printing system according to the first exemplary embodiment prevents a sheet holding unit, if it is determined to be used in a selected hold job (or print job), from being selected when the mismatch sheet attribute information is set to the sheet holding unit. Therefore, the printing system according to the first exemplary embodiment can prevent the printing of another job from being stopped because of a new media mismatch that may occur when a user erroneously changes the setting of attribute information about the sheet holding unit to be used in the selected hold job (or print job). 
     According to the example illustrated in the sheet holding unit selection screen  1511  in  FIG. 15B , each sheet holding unit to be used in the selected hold job (or print job) is brought into a gray-out state to prevent the sheet holding unit from being selected by the user, as mentioned above. However, the screen display is not limited to the above-mentioned example. For example, it is useful to allow each user to arbitrarily select the sheet holding unit to be used in the selected hold job (or print job), instead of bringing the sheet holding unit into a gray-out state. In this case, the printing system can be configured to notify a user of a possibility that the printing of another job may stop when the above-mentioned sheet holding unit is selected by the user. 
     In the first exemplary embodiment, if it is determined that the mismatch sheet attribute information is not settable to all sheet holding units provided in the printing apparatus, as a result of the mismatch sheet attribute information settable sheet holding unit determination processing, it is useful to instruct a user to release the mismatch job from the selected state. In this case, in step S 1209  illustrated in  FIG. 12 , the CPU  212  displays a warning screen  1601  illustrated in  FIG. 16A , instead of displaying the sheet holding unit selection screen  1511  illustrated in  FIG. 15B  on the operation unit  204 . While confirming the warning screen  1601 , the user can know that the printing of a job that uses the mismatch sheet is unfeasible because the attribute information about the sheet to be used in the mismatch job cannot be set to all sheet holding units. If a user selects the mismatch sheet on the warning screen  1601  and presses a selection release button  1602 , the mismatch job can be released from the selected state. If the mismatch job is released from the selected state on the warning screen  1601  and each hold job being in selected state is brought into non-mismatch state, the printing system can cause the operation unit  204  to display a notification screen  1611  illustrated in  FIG. 16B . While confirming the notification screen  1611 , the user can know that the printing of the hold job being in selected state can be immediately started because the attribute information about the sheet to be used in the hold job being in selected state is set to all sheet holding units. 
     As mentioned above, to solve the media mismatch state, the printing system according to the first exemplary embodiment prevents a sheet holding unit, if it is determined to be used in a selected hold job (or print job), from being selected when the mismatch sheet attribute information is set to the sheet holding unit. 
     However, if it is determined that all sheet holding units provided in the printing apparatus can be used for a selected hold job (or print job), it becomes unfeasible to set the mismatch sheet attribute information to the sheet holding unit to solve the media mismatch state. 
     On the other hand, it is general that the priority of each job is taken into consideration in printing. Therefore, a user may want the printing system to start the printing of a higher-priority job at timing earlier than the printing of a lower-priority job. 
     In view of the foregoing, to solve the media mismatch (sheet type inconsistent) state, a printing system according to a second exemplary embodiment prevents a sheet holding unit, if it is determined to be used in a higher-priority job, from being selected when the mismatch sheet attribute information is set to the sheet holding unit. On the other hand, the printing system according to the second exemplary embodiment allows a user to select a sheet holding unit to be used in a lower-priority job so that the mismatch sheet attribute information can be set to the sheet holding unit, as described below. 
     The printing system according to the second exemplary embodiment has a configuration that is similar to that described in the first exemplary embodiment. The digital printing machine  102  and the computer  101  are connected via the network  100 . Further, a function block diagram illustrating a functional configuration of the digital printing machine  102  according to the second exemplary embodiment is similar to that described in the first exemplary embodiment. A hardware block diagram illustrating a system configuration of the computer (PC)  101  according to the second exemplary embodiment is similar to that described in the first exemplary embodiment. Therefore, redundant description thereof will be avoided. Sequential flowcharts illustrating processing to be performed by the digital printing machine  102  according to the second exemplary embodiment are similar to those illustrated in  FIGS. 6 to 13  described in the first exemplary embodiment. Therefore, redundant description thereof will be avoided. The second exemplary embodiment is different from the first exemplary embodiment in the content of the mismatch sheet attribute information settable sheet holding unit determination processing. 
       FIG. 19  is a flowchart illustrating the processing that can be performed by the printing system according to the second exemplary embodiment to display a screen that allows a user to select a mismatch sheet attribute information settable sheet holding unit. The processing according to the flowchart illustrated in  FIG. 19  is comparable to the processing performed in step S 1200  illustrated in  FIG. 11 . In the flowchart illustrated in  FIG. 19 , the same step number is used to denote a step if the processing to be performed in the step is similar to that described in the first exemplary embodiment with reference to  FIG. 12 . Hereinafter, differences between the processing in  FIG. 19  and the processing in  FIG. 12  are mainly described. 
     If the determination result in step S 1204  indicates that the mismatch sheet attribute information is settable to the target sheet holding unit determined in step S 1202  (YES in step S 1204 ), the operation proceeds to step S 1901 . 
     In step S 1901 , the CPU  212  determines whether there is any job selected from the hold job list  1402 , which is earlier in selection order than the mismatch job and uses the sheet stored in the target sheet holding unit determined in step S 1202 . As illustrated in  FIG. 14B , a numerical value of each selection mark ( 1421 ,  1422 , or  1423 ) displayed on the left side of the job name field indicates the selection order of the hold job. 
     If the determination result in step S 1901  indicates that there is not any hold job that is earlier in selection order and uses the sheet stored in the target sheet holding unit determined in step S 1202  (NO in step S 1901 ), the operation proceeds to step S 1206  to perform subsequent processing. On the other hand, if it is determined that there is a hold job that is earlier in selection order and uses the sheet stored in the target sheet holding unit determined in step S 1202  (YES in step S 1901 ), the operation proceeds to step S 1208  to perform the above-mentioned processing. 
     As mentioned above, the processing that can be performed by the printing system according to the second exemplary embodiment is different from that described in the first exemplary embodiment. 
       FIG. 20  illustrates a determination result with respect to the mismatch sheet attribute information settable sheet holding unit according to the second exemplary embodiment. 
     According to the example illustrated in  FIG. 20 , attribute information about the sheet to be set (mismatch sheet) is “A4 Paper1”. Further, it is restricted in such a way that the A3 sheet cannot be set to the sheet holding unit  1 . Job H, Job I, Job J, and Job K are target selection jobs (hold jobs) to be sequentially subjected to the determination processing in step S 1304 . The paper to be used in the Job H is “A4 plain paper”. The paper to be used in the Job I is “A4 Paper1”. The paper to be used in the Job J is “A3 plain paper”. The paper to be used in the Job K is “A3 thick paper”. Further, the “A4 Paper1” to be used in the Job I and the “A3 thick paper” to be used in the Job K are not set to any sheet holding unit. In other words, these papers are mismatch sheets. Therefore, the inconsistency mark  1431  is displayed in association with each mismatch sheet. For example, the media mismatch (sheet type inconsistent) state can be solved by setting the mismatch sheet (i.e., “A4 Paper1”) of the Job I to the sheet holding unit, as described below. The Job H has a priority level higher than that of the Job I, because the Job H is ranked as the first hold job in the selection order. On the other hand, the Job I is ranked as the second hold job in the selection order. Further, each print job (i.e., Job V and Job W) has a priority level higher than those of the hold jobs (i.e., Job H, Job I, Job J, and Job K). As illustrated in  FIG. 20 , each of the sheet holding unit  1 , the sheet holding unit  2 , the sheet holding unit  3 , and the sheet holding unit  6  is determined as the sheet holding unit to which the “A4 Paper1” is settable. 
     Then, in step S 1209  illustrated in  FIG. 19 , the CPU  212  causes the operation unit  204  to display a sheet holding unit selection screen  2101  on which each of the sheet holding unit  4  and the sheet holding unit  5  (i.e., the sheet holding units to which the “A4 Paper1” is not settable) is brought into a gray-out state as illustrated in  FIG. 21 . Therefore, the sheet holding unit  4  and the sheet holding unit  5  cannot be selected. 
     As described above, to solve the sheet type inconsistent state, the printing system according to the second exemplary embodiment prevents a sheet holding unit, if it is determined to be used in a hold job (or print job) having a priority level higher than that of the mismatch job, from being selected when the mismatch sheet attribute information is set to the sheet holding unit. 
     Therefore, even if a user erroneously changes the setting of the attribute information about the sheet holding unit to be used in the job being higher than the mismatch job in priority level, the printing system according to the second exemplary embodiment can prevent the printing of another higher-priority job from being stopped due to a newly induced media mismatch. 
     Further, the printing system according to the second exemplary embodiment allows a user to select a sheet holding unit to be used in a job having a priority level lower than that of the mismatch job when the mismatch sheet attribute information is set to the sheet holding unit. However, if there is a sheet holding unit that is not used in a selected hold job (or print job), the printing system according to the second exemplary embodiment can prevent a user from selecting the sheet holding unit to be used in the job being lower than the mismatch job in priority level. 
     Further, the printing system according to the second exemplary embodiment refers to the mismatch job selection order, with respect to the hold job, in discriminating a higher-priority job from a lower-priority job. However, the discrimination method is not limited to the above-mentioned example. For example, if the usage history of individual hold jobs can be stored in the HDD  209 , it is useful to refer to the usage history of each job in discriminating a higher-priority job from a lower-priority job. 
     The present invention is not limited to the above-mentioned exemplary embodiments and can be modified in various ways (including any possible combination of the above-mentioned exemplary embodiments) within the scope of the present invention. 
     For example, in the present exemplary embodiment, the CPU (i.e., the control unit) of the digital printing machine  102  is configured to perform the above-mentioned various controls. However, an external controller (serving as a printing control apparatus) can be provided separately from the digital printing machine  102  and can be configured to perform a part or the whole of the above-mentioned various controls. 
     Although the present invention has been described based on various exemplary embodiments, it is apparent to a person skilled in the art that the scope or the gist of the present invention is not limited to a specific part of the description. 
     Other Embodiments 
     Embodiments of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions recorded on a storage medium (e.g., non-transitory computer-readable storage medium) to perform the functions of one or more of the above-described embodiment(s) of the present invention, and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more of a central processing unit (CPU), micro processing unit (MPU), or other circuitry, and may include a network of separate computers or separate computer processors. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.