KR20040049566A - Data processor apparatus and method for digital data broadcasting - Google Patents

Abstract

PURPOSE: A data processing device for digital data broadcasting is provided to efficiently transmit data in consideration of a limited transmission bandwidth and a receiver memory, thereby increasing a reacting speed of data in a receiver. CONSTITUTION: A data server(17) comprises as follows. A data server controller(21) controls generation of a data message according to contents layer information. A control message generator(22) generates a data control message according to a control signal of the data server controller(21). A data message generator(23) generates the data message according to the control signal of the data server controller(21). A multiplexer(24) multiplexes the data control message and the data message according to the control signal, and outputs the multiplexed messages.

Description

Data processor apparatus and method for digital data broadcasting TECHNICAL FIELD

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data processing apparatus for digital data broadcasting, and a method and a computer readable recording medium recording a program for realizing the method. In particular, the present invention efficiently transmits data in consideration of a limited transmission bandwidth and a receiver memory. And a computer readable recording medium having recorded thereon a program for realizing the method.

The viewer feels great inconvenience in using the receiver when there is no immediate response when selecting specific data among the data provided by the digital data broadcast. This may cause the user to avoid using data broadcasting. Without considering the receiver's data processing capability, the transmitting side allocates high transmission bandwidth to maximize the response speed of the data selected by the user, or the transmitted side transmits the data immediately so that the receiving side can process the data selected by the user. The data can be stored in memory in advance. However, since the transmission bandwidth used for broadcasting and the memory capacity of the receiver are limited, there is a limit to increasing the response speed. As such, a method for efficiently transmitting and receiving data has been studied in order to maximize the response speed of the data under the limited data transmission bandwidth and the receiver memory capacity. As a representative study, the transmitting side allocates and transmits higher bandwidth for data with a higher probability of user access in a limited transmission bandwidth, and the receiving side gives higher priority to data with a higher number of user accesses and lower transmission bandwidth. Has been proposed to import into the receiver and store in memory [Acharya].

However, the transmission method is difficult to apply to the actual digital data broadcast because a specific access criteria for determining the access probability of the data is not presented.

Also, due to the contental relationship among the data, it is possible to know what data is next accessible according to the data selected by the current user. The receiving method does not take this into consideration and determines the receiving priority only by the number of past user accesses. There is an inefficiency in speeding up the response of data.

In order to solve the problems of the conventional method, an access criterion applicable to actual broadcasting and a transmission technique implemented accordingly are required.

In addition, according to the transmission method, a technique for calculating a reception priority for determining which data to store first in a limited memory of the receiver is required.

The present invention has been proposed to meet the above-mentioned requirements. In the digital data broadcasting service, data processing for digital data broadcasting for efficiently transmitting data in consideration of a limited transmission bandwidth and a receiver memory is provided. An object of the present invention is to provide an apparatus, a method thereof, and a computer-readable recording medium having recorded thereon a program for realizing the method.

1 is an exemplary configuration diagram of a data broadcast transmission system to which the present invention is applied.

2 is a block diagram of an embodiment of a data processing apparatus for digital data broadcasting according to the present invention;

3 is a flowchart illustrating an embodiment of a data processing method for digital data broadcasting according to the present invention;

4 is a detailed flowchart illustrating an embodiment of a process of generating a DSM-CC control message and a data message in a data processing method for digital data broadcasting according to the present invention;

5 is a flow diagram of one embodiment of a method for receiving data transmitted efficiently in accordance with the present invention.

6A to 6C are exemplary diagrams illustrating a hierarchical structure of data and a two-layer structure of a data carousel and a transmission frequency of a group according to the present invention.

7 is an exemplary view of a reception priority of data according to the present invention when the hierarchical structure of data is set according to FIG. 6;

* Explanation of symbols for the main parts of the drawings

21: data server control unit 22: control message generation unit

23: data message generator 24: multiplexer

According to an aspect of the present invention, there is provided a transmission data processing apparatus for digital data broadcasting, comprising: data server control means for controlling generation of a data message according to content layer information input from the outside; Control message generating means for generating a data control message according to a control signal of said data server control means; Data message generating means for generating a data message according to a control signal of said data server control means; And multiplexing means for multiplexing and outputting the data control message and the data message according to the control signal of the data server control means.

The present invention also provides a transmission data processing method applied to a data processing apparatus for digital data broadcasting, comprising: a first step of receiving data analysis information from an external multiplexing manager or a user; Classifying data into groups according to the analyzed data layer information; Generating a digital storage media command and control (DSM) section including data layer information and connection information according to the classified group; And a fourth step of generating the MPEG-2 transport stream from the generated DSM-CC section and assigning and outputting a transmission frequency of a group according to transmission priority.

In addition, the present invention, in the received data processing method applied to the data processing apparatus for digital data broadcasting, analyzing the Download Server Initiate (DSI) control message from the data transmitted to the Digital Storage Media-Command and Control (DSM-CC) section A first step of extracting a transmission frequency of the data; A second step of extracting connection information between data by analyzing a DownloadInfoIndication (DII) control message from data transmitted to the DSM-CC section, and restoring layer information of the data; A third step of calculating a distance from the data selected in the current terminal to each data from the data layer information; A fourth step of calculating a reception cost of each data based on the transmission frequency and the distance of the data; And a fifth step of determining a reception priority according to the reception cost.

The present invention also provides a data processing method applied to a data processing apparatus for digital data broadcasting, comprising: a first step of receiving and analyzing data layer information from an external multiplexing manager or a user; Classifying data into groups according to the analyzed data layer information; Generating a digital storage media command and control (DSM) section including data layer information and connection information according to the classified group; Generating a MPEG-2 transport stream from the generated DSM-CC section and assigning and outputting a transmission frequency of a group according to a transmission priority; DSI (DSI) from data transmitted to the DSM-CC section; A fifth step of analyzing a DownloadServerInitiate) control message and extracting a transmission frequency of data; A sixth step of extracting connection information between data by analyzing a DownloadInfoIndication (DII) control message from the data transmitted to the DSM-CC section, and restoring hierarchical information of the data; A seventh step of calculating a distance from the data selected in the current terminal to each data from the data layer information; An eighth step of calculating a reception cost of each data based on the transmission frequency and the distance of the data; And a ninth step of determining a reception priority according to the reception cost.

The present invention also provides a data processing apparatus having a processor, comprising: a first function of receiving data layer information from an external multiplexing manager or a user and analyzing the data layer information; A second function of classifying data into groups according to the analyzed data layer information; A third function of generating a digital storage media command and control (DSM) section including data layer information and connection information according to the classified group; And a program for realizing a fourth function of generating the MPEG-2 transport stream from the generated DSM-CC section and assigning and outputting the transmission frequency of the group according to the transmission priority. Provide a record carrier.

The present invention also provides a data processing apparatus having a processor, which analyzes a Download Server Initiate (DSI) control message from data transmitted to a Digital Storage Media-Command and Control (DSM-CC) section and extracts a data transmission frequency. 1 function; A second function of extracting connection information between data by analyzing a DownloadInfoIndication (DII) control message from data transmitted to the DSM-CC section, and restoring layer information of the data; A third function of calculating a distance from the data selected in the current terminal to each data from the data layer information; A fourth function of calculating a reception cost of each data through the transmission frequency and the distance of the data; And a computer readable recording medium having recorded thereon a program for realizing a fifth function of determining a reception priority according to the reception cost.

The present invention also provides a data processing apparatus having a processor, comprising: a first function of receiving data layer information from an external multiplexing manager or a user and analyzing the data layer information; A second function of classifying data into groups according to the analyzed data layer information; A third function of generating a digital storage media command and control (DSM) section including data layer information and connection information according to the classified group; A fourth function of generating an MPEG-2 transport stream from the generated DSM-CC section and assigning and outputting a transmission frequency of a group according to transmission priority; A fifth function of extracting a transmission frequency of data by analyzing a DownloadServerInitiate (DSI) control message from the data transmitted to the DSM-CC section; A sixth function of extracting connection information between data by analyzing a DownloadInfoIndication (DII) control message from the data transmitted to the DSM-CC section, and restoring layer information of the data; A seventh function of calculating a distance from the data selected in the current terminal to each data from the data layer information; An eighth function of calculating a reception cost of each data based on a transmission frequency and a distance of the data; And a computer readable recording medium having recorded thereon a program for realizing a ninth function of determining a reception priority according to the reception cost.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is an exemplary configuration diagram of a data broadcast transmission system to which the present invention is applied.

As shown in FIG. 1, an ATSC (Advanced Television Systems Committee) based data broadcasting transmission system includes a video / audio encoder (11, 12), a program multiplexer (13), and a program multiplexer (13). , A data server (data processing unit) 17, a PSIP (Program and System Information Protocol for Terrestrial Broadcast and Cable) server 14, an emission multiplexer 15, and a multiplexer manager (18) is provided.

The operation of the ATSC-based data broadcasting transmission system having the above structure will be described in detail as follows.

The video / audio encoders 11 and 12 are video encoders 11 which generate a video stream compressed and encoded according to the MPEG-2 video standard, and audio streams which are compression coded according to the AC (Audio Coding) -3 standard. The audio encoder 12 is configured to output a compression-enriched video / audio stream to the program multiplexer 13.

The program multiplexer 13 compresses the encoded video / audio elementary stream through the video / audio encoders 11 and 12 into a packetized elementary stream (PES), MPEG-2 transport stream according to the MPEG-2 system standard. After packetizing a transport stream, the general function of multiplexing them to create one MPEG-2 transport stream, the additional data MPEG-2 transport stream packet input from the data server 17, and the video / audio transport MPEG- It has an additional function of outputting to the transmission multiplexer 15 one MPEG-2 transport stream multiplexed with two transport stream packets.

The data server 17 functions as a digital storage media command and control (DSM-CC) section defined in A / 90, which is an ATSC data broadcasting standard document, to encapsulate additional data and output the same to the transmission multiplexer 15.

The PSIP server 14 includes a PSIP table, a program association table (PAT) and a program map table (PMT) and a data service table (DST) and a network resource (NRT) for transmission of program information. Table) and the like and output to the transmission multiplexer 15.

The delivery multiplexer 15 functions to multiplex each transport stream for the PSIP table, video / audio and additional data to generate and transmit one MPEG-2 transport stream.

The multiplexing manager 18 controls the PSIP server 14 to transmit broadcast program formation information, and also controls the program multiplexer 13 and data server 17 to transmit additional data.

2 is a block diagram of an embodiment of a data processing apparatus for digital data broadcasting according to the present invention.

As shown in FIG. 2, the data server (data processing apparatus) 17 according to the present invention includes a data server controller 21 for controlling data message generation according to content layer information input from the outside, and a data server. The control message generator 22 for generating the data control message according to the control signal of the controller 21 and the data message generator 23 for generating the data message according to the control signal of the data server controller 21. And a multiplexer 24 for multiplexing and outputting a data control message and a data message according to a control signal of the data server controller 21.

The operation of the data processing apparatus for digital data broadcasting according to the present invention having the above structure will be described in detail as follows.

The data server controller 21 controls a control message generator 22 that generates a data control message and data that generates a data message according to hierarchical information of data received from an external multiplexing manager 18 or a user. A function of controlling the message generator 23 and a function of controlling the multiplexer 24 for multiplexing and outputting messages input from the control message generator 22 and the data message generator 23 are performed.

The control message generator 22 generates a Download Server Initiate (DSI) control message and a DownloadInfoIndication (DII) control message of the DSM-CC section defined in A / 90 and outputs the generated control message to the multiplexer 24. In addition, the DSI control message into which the level information of the data is inserted and the DII control message into which the connection information of the data is inserted are generated and output to the multiplexer 24.

The data message generator 23 generates data as a DDB (DownloadDataBlock) data message of the DSM-CC section defined in A / 90 and outputs the data to the multiplexer 24.

The multiplexer 24 transmits the multiplexer 15 according to the transmission frequency assigned to the message received from the control message generator 22 and the data message generator 23 according to the control signal of the data server controller 21. )

Next, an operation process of the data processing apparatus for digital data broadcasting according to the present invention having the structure as described above will be described in more detail with reference to FIGS. 3 to 4.

3 is a flowchart illustrating a data processing method for digital data broadcasting according to the present invention.

As shown in FIG. 3, the data server (data processing apparatus) 17 according to the present invention analyzes hierarchical information of data received from an external multiplexing manager 18 or a user (301).

Subsequently, the data server 17 classifies the data at the same level into the same group according to the data hierarchy information (302). The data at the top level is the data that the user needs to access for the first time, which is the main menu of data. The main menu provides access to the data in that submenu. On average, the user access probability of the main menu is high, so the transmission frequency is set to the shortest.

In other words, the higher the group, the shorter the transmission frequency. The data server transmits the group level value using the DSI message to inform the receiving party of the group's transmission frequency.

Subsequently, the data server must transmit the connection information between the data modules as well as the group level in order to determine the reception priority at the receiving side. The reception priority of each data module varies depending on which data module is the currently selected data module. This is because a data module accessible by the user is currently determined in the data module selected by the user, and access to other data modules is possible only after accessing the data module by several levels. Therefore, by transmitting the connection information between the data modules to the receiving side, it is possible to restore the hierarchical information of the data so that the steps (number of branches and distance) between the data modules can be known from the data module selected by the user. In order to transmit the connection information between data modules to the receiver, module_list_descriptor is defined and inserted into the DII message.

Finally, the data server 17 generates a DSM-CC control message and a data message (303), packetizes the generated message into an MPEG-2 transport stream (TS), and outputs it in accordance with the transmission frequency (304).

A specific method for inserting the level of the group proposed by the present invention is to inform the receiver of the level of data using a Download Server Initiate (DSI) message defined in ATSC-A / 90. However, since DSI does not have fields to define them, the levels of groups are described using groupsinfoPrivateDataByte of GroupInfoIndication () structure and defined as follows.

groupsinfoPrivateDataByte () {

group_level

}

The group_level of the method is set as the transmission frequency is set higher as the level of the group in the hierarchical structure of the data, and set as lower as the level is lower.

In addition, a specific method for inserting the connection information of each data module proposed in the present invention is to inform the receiver of the connection information of the module using the DII control message defined in ATSC-A / 90. Data module connection information inserts user defined "module_list_descriptor" into "moduleDescription structure" of DII. "module_list_descriptor" is composed of "descriptor_tag", descriptor_length, "list_type" and "module_id" and is represented as follows.

module_list_descriptor () {

descriptor_tag (user private)

descriptor_length

for (i = 0; i <N; i ++) {

list_type

module_id

}

}

In the above descriptor, "list_type" is set to 0x00 when representing the upper module "module_id" and "list_type" is set to 0x01 when indicating the lower module_id.

In addition, a detailed method for calculating the reception priority of the receiver proposed by the present invention is as follows.

Information required for the reception priority calculation is the group level and the connection information of the data module.

Here, the level of the group and the connection information of the data module are values determined according to the hierarchical structure of the data, and the reception cost, which is a measure by which the receiving side determines the reception priority of the data, takes into account the transmission frequency and distance of the corresponding data module. It is calculated as in [Equation 1] below. The lower the reception cost, the higher the reception priority.

Receive Cost = Distance + Transmission Frequency

Distance = the number of branches required to reach that module from the module currently selected

Transmission frequency = (1-level of the module / total group)

FIG. 4 is a detailed flowchart illustrating a DSM-CC control message and a data message generating process 33 in a data processing method for digital data broadcasting according to the present invention.

As shown in FIG. 4, in order to generate the DSM-CC control message and the data message, the level information of each group allocated to the data is inserted into the DSI, the connection information of each data module is inserted into the DSI, and the respective data are inserted into the DDB. To create.

That is, the type of the DSM-CC section is determined (401). If the DSM-CC section is a DSI control message, the level information of the group is inserted (402) and encoded into the DSI section (403). In this DII control message, the connection information between the modules is inserted according to the layer information (404) and encoded into the DII section (405). If the DSM-CC section is a DDB data message, the data is divided into blocks (406) and encoded into the DDB section. (407).

Subsequently, the DSI control message, the DII control message, and the DDB data message of the DSM-CC section are packetized into an MPEG-2 transport stream through the data server, and each of them is output according to the transmission frequency (408).

5 is a flowchart of an embodiment of a method for receiving data transmitted efficiently according to the present invention.

As shown in FIG. 5, DSI is analyzed in the transmitted stream to extract level information for each group, and DII is analyzed to extract connection information between data modules. The reception cost for each data module is calculated using the extracted level information and the connection information of the data module selected at the current receiver, and the low cost data module is stored in the receiver memory.

Looking at this in more detail, it extracts the transmission period of the group through the DSI analysis (501), and restores the layer information through the DII analysis (502).

Subsequently, the selected data module is examined at the current terminal (503), the reception cost of each module for the selected data module is calculated (504), and the module having a small reception cost value is stored in the memory (505).

Thereafter, the method determines whether or not to change the data selection (506) and if there is a data selection change, the process proceeds to step 503 of checking the data module selected in the current terminal.

6A to 6C are exemplary diagrams illustrating a hierarchical structure of data according to the present invention, a two-layer structure of data carousel, and a transmission frequency of a group.

As shown in Figs. 6A to 6C, the data in the data hierarchy has a hierarchy of level 3, and the level 1 data should be selected when the user first accesses the data as the top main menu (Main 1). As a data module, the user is likely to choose on average. Level 2 data modules Sub 11 and Sub 12 represent data accessible from the main menu Main 1. In addition, the level 3 data modules Sub 111, Sub 112, Sub 121, and Sub 122 are data accessible from the level 2 data modules Sub 11 and Sub 12, and the user is most likely to select on average. Data modules with the same level are organized into a group so that the higher the level, the shorter the transmission frequency.

7 is a diagram illustrating a reception priority of data according to the present invention when the hierarchical structure of data is set according to FIG. 6.

As shown in FIG. 7, the current user selected data is Sub 11. In Sub 11, the data accessible to the user are Main1, Sub111, and Sub112, so the reception priority of this data is higher than that of other data. However, since Main1 has a higher transmission frequency than Sub111 and Sub112, in order to increase the average access success rate of data, Sub1 1 and Sub112 data are first received. If the reception priority is the same, the data with the larger size is received first. The distance, transmission frequency, reception cost, and reception priority of each module in Sub 11 are shown in Table 1 below.

The method of the present invention as described above may be implemented as a program and stored in a computer-readable recording medium (CD-ROM, RAM, ROM, floppy disk, hard disk, magneto-optical disk, etc.).

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes are possible in the art without departing from the technical spirit of the present invention. It will be clear to those of ordinary knowledge.

As described above, the present invention can be utilized to increase the response speed of data in a receiver having a limited transmission bandwidth and a limited memory for a data broadcasting service.

Claims (13)

In the transmission data processing apparatus for digital data broadcasting, Data server control means for controlling data message generation according to content layer information input from the outside; Control message generating means for generating a data control message according to a control signal of said data server control means; Data message generating means for generating a data message according to a control signal of said data server control means; And Multiplexing means for multiplexing and outputting a data control message and a data message according to a control signal of said data server control means Transmission data processing apparatus for digital data broadcasting comprising a. The method of claim 1, The data server control means, The control message generating means and the data message generating means are controlled according to hierarchical information of data input from an external multiplexing manager or a user, and the messages inputted from the control message generating means and the data message generating means are multiplexed and output. And a transmission means for controlling the multiplexing means. The method according to claim 1 or 2, The control message generating means, Transmitting data processing for digital data broadcasting by generating a DSI (Download Server Initiate) control message in which data level information is inserted and a DII (DownloadInfoIndication) control message in which connection information of data is inserted and outputting them to the multiplexing means. Device. The method of claim 4, wherein The multiplexing means, Transmission data processing for digital data broadcasting according to the control signal of the data server control means, according to the transmission frequency allocated to the message received from the control message generating means and the data message generating means to the multiplexer; Device. In the transmission data processing method applied to a data processing device for digital data broadcasting, A first step of receiving and analyzing data layer information from an external multiplexing manager or a user; Classifying data into groups according to the analyzed data layer information; Generating a digital storage media command and control (DSM) section including data layer information and connection information according to the classified group; And A fourth step of generating an MPEG-2 transport stream from the generated DSM-CC section and assigning and outputting a transmission frequency of a group according to transmission priority; Transmission data processing method for digital data broadcasting comprising a. The method of claim 5, wherein The second step, A method of processing transmission data for digital data broadcasting, comprising describing a level of data using groupsinfoPrivateDataByte of a GroupInfoIndication () structure of a DownloadServerInitiate (DSI) control message. The method according to claim 5 or 6, The second step, A method of processing transmission data for digital data broadcasting, using the module_list_descriptor of a DownloadInfoIndication (DII) control message to describe connection information between data modules. In the received data processing method applied to a data processing apparatus for digital data broadcasting, A first step of extracting a transmission frequency of data by analyzing a DownloadServerInitiate (DSI) control message from data transmitted to a Digital Storage Media (Command & Control) section; A second step of extracting connection information between data by analyzing a DownloadInfoIndication (DII) control message from data transmitted to the DSM-CC section, and restoring layer information of the data; A third step of calculating a distance from the data selected in the current terminal to each data from the data layer information; A fourth step of calculating a reception cost of each data based on the transmission frequency and the distance of the data; And A fifth step of determining a reception priority according to the reception cost Receive data processing method for digital data broadcasting comprising a. The method of claim 8, The third step, A reception data processing method for digital data broadcasting, characterized in that the reception cost is calculated by the following [Equation] to determine the reception priority. [Equation] Receive Cost = Distance + Transmission Frequency Distance = the number of branches required to reach that module from the module currently selected Transmission frequency = (1-level of the module / total group) In the data processing method applied to a data processing apparatus for digital data broadcasting, A first step of receiving and analyzing data layer information from an external multiplexing manager or a user; Classifying data into groups according to the analyzed data layer information; Generating a digital storage media command and control (DSM) section including data layer information and connection information according to the classified group; Generating a MPEG-2 transport stream from the generated DSM-CC section and assigning and outputting a transmission frequency of a group according to transmission priority; A fifth step of extracting a transmission frequency of the data by analyzing a DownloadServerInitiate (DSI) control message from the data transmitted to the DSM-CC section; A sixth step of extracting connection information between data by analyzing a DownloadInfoIndication (DII) control message from the data transmitted to the DSM-CC section, and restoring hierarchical information of the data; A seventh step of calculating a distance from the data selected in the current terminal to each data from the data layer information; An eighth step of calculating a reception cost of each data based on the transmission frequency and the distance of the data; And A ninth step of determining a reception priority according to the reception cost Data processing method for digital data broadcasting comprising a. In a data processing apparatus having a processor, A first function of receiving and analyzing data layer information from an external multiplexing manager or a user; A second function of classifying data into groups according to the analyzed data layer information; A third function of generating a digital storage media command and control (DSM) section including data layer information and connection information according to the classified group; And A fourth function of generating an MPEG-2 transport stream from the generated DSM-CC section and assigning and outputting a transmission frequency of a group according to transmission priority A computer-readable recording medium having recorded thereon a program for realizing this. In a data processing apparatus having a processor, A first function of extracting a transmission frequency of data by analyzing a DownloadServerInitiate (DSI) control message from data transmitted to a Digital Storage Media-Command and Control (DSM-CC) section; A second function of extracting connection information between data by analyzing a DownloadInfoIndication (DII) control message from data transmitted to the DSM-CC section, and restoring layer information of the data; A third function of calculating a distance from the data selected in the current terminal to each data from the data layer information; A fourth function of calculating a reception cost of each data through the transmission frequency and the distance of the data; And A fifth function of determining a reception priority according to the reception cost A computer-readable recording medium having recorded thereon a program for realizing this. In a data processing apparatus having a processor, A first function of receiving and analyzing data layer information from an external multiplexing manager or a user; A second function of classifying data into groups according to the analyzed data layer information; A third function of generating a digital storage media command and control (DSM) section including data layer information and connection information according to the classified group; A fourth function of generating an MPEG-2 transport stream from the generated DSM-CC section and assigning and outputting a transmission frequency of a group according to transmission priority; A fifth function of extracting a transmission frequency of data by analyzing a DownloadServerInitiate (DSI) control message from the data transmitted to the DSM-CC section; A sixth function of extracting connection information between data by analyzing a DownloadInfoIndication (DII) control message from the data transmitted to the DSM-CC section, and restoring layer information of the data; A seventh function of calculating a distance from the data selected in the current terminal to each data from the data layer information; An eighth function of calculating a reception cost of each data based on a transmission frequency and a distance of the data; And A ninth function of determining a reception priority according to the reception cost A computer-readable recording medium having recorded thereon a program for realizing this.