JPH0784849A - Data access control method - Google Patents

Abstract

PURPOSE:To perform control so that plural users can obtain the latest data at all times when accessing a database. CONSTITUTION:If one user retrieves data at the time of access to the database of a host 101 from terminals 102-104 the terminals request update data of the host at specific intervals of time. The update data are data which are recorded each time the database is updated so that the update contents of the host 101 can be known. The terminals update data corresponding to the update data among data held at hand on the basis of the update data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data access method in a database system or a file system for accumulating data and updating / searching the accumulated data.

[0002]

2. Description of the Related Art In a conventional database system, when a plurality of users use a database,
A method is known in which, when data referenced by a certain user is updated by another user, the updated data is first notified when the data is referenced again. Also, when a user tries to update data, if the same data is updated by another user between the time when the data is read and the time when the data is updated, the update by the user who started the update first will be completely lost. It can be meaningless. In order to prevent this, exclusive control is performed when updating data.

[0003]

However, in the above method, since there is a large time difference between the time when the update occurs and the time when the user who refers to the data confirms the communication content, the user refers to it now. There was no guarantee that the existing data was the latest data. In addition, when exclusive control is performed, during communication of certain data, even if another user tries to update the data, the user must wait for the previous update to end, and multiple users can search or update the same data. There was a problem that it took time when such access occurred. In view of the above-mentioned conventional example, it is an object of the present invention to provide a data access control method that guarantees that the data to be referred to is always the latest and that the same data can be updated simultaneously by a plurality of users.

[0004]

In order to achieve the above object, the data access control method of the present invention has the following configuration. A data access control method for controlling access to data by a plurality of users, comprising a recording step of recording a data update history, a data reading step of reading desired data, and a read of the update history recorded by the recording step. An update history reading step and an updating step of updating the data read by the data reading step based on the update history read by the history reading step.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A database system according to an embodiment of the present invention will be described below with reference to the accompanying drawings. <Structure> FIG. 1 is a diagram showing the structure of the database system of this embodiment. In the figure, a host 101 is a host computer that functions as a database server, and three terminal devices 102 to 102 are connected by a communication cable 105.
It is connected to 104. The user retrieves or updates common or personal data from each terminal.

FIG. 2 is a block diagram of the host 101. In the figure, a CPU 201 controls the entire apparatus by executing a program stored in a memory 202 and realizes a database system. The memory 202 is used to store programs and other necessary data. Required data includes dictated update files. The disk memory 203 stores data forming a database. Communication interface 20
Reference numeral 4 is connected to the communication cable 105 and controls communication with the terminal. These blocks are connected by a bus 205.

FIG. 3 is a diagram showing the configuration of each of the terminal devices 102 to 104. In the figure, a CPU 301 controls the entire apparatus by executing a program stored in a memory 302. In the memory 302, an area for holding the data read from the database other than the program and other work areas are secured. The keyboard 303 is an input unit for an operator to input data and the like. The display 304 displays data read from the database,
Information to inform the operator is displayed. The communication interface 305 is an interface for communicating with the host 101. These blocks are connected by a bus 306. <Access to database> Operator is terminal 102
~ 104 to access the database. When referring to data, search conditions are input and sent as a search request to the host 101. The host 101 searches for data that meets the conditions and returns the obtained data to the terminal.

When updating the data, when the operator specifies the data to be updated, the terminal sends a search request to the host 101 together with the specification. This search request is only for reading data, and it is not necessary to lock the data to be updated. This point will be described later. The host 101 returns the data designated by the terminal to the terminal. The terminal performs the desired operation on the obtained data and sends an update request to the host to write it again in the database. The host 101 updates the database according to the update request.

When updating data, the host 101 saves the updated data in a dedicated memory area called an update file for recording a history of updates. Terminal 102
In ~ 104, while accessing the database,
This update file is read out periodically, and if the data in the update file is retained as the internal data of the terminal, the internal data of the terminal is updated by the contents of the update file only for the necessary part (this is the difference calculation Called). The above is the outline of the process when the operator accesses the database, which will be described in more detail with reference to FIGS. 4 to 6. <Processing by Terminal> FIG. 4 is a flowchart showing the procedure of database searching or updating processing by the terminal. This procedure is realized by the CPU 301 executing the program stored in the memory 302.

Data reference / update is started by a request from the terminal. First, in step S701, the operator is prompted to input the conditions for the data to be searched.
Then, the condition is sent to the host 101 as a search request, and the response is waited for. The search condition input at this time is stored in a predetermined area in the memory 302. Step S
In 703, the search result is tested, and if the search is unsuccessful, that is, if some data is not found, it is determined that the data to be searched / updated does not exist in the database, and the processing ends.

If the search is successful, step S704.
Then, the data returned from the host 101 is stored in the internal data area of the memory 302. When the terminal processes the data obtained from the database, the data stored in this internal data area is used. If the data can be obtained, the timer built in the CPU 301 is set to a predetermined time and activated in step S705. This timer will CP it when the set time has elapsed.
Notify U301.

Thereafter, in step S706, it is determined whether the process currently performed by the operator is data reference or update, and the process branches depending on the result. If it is reference processing, the obtained data is used to perform step S707.
After that, desired processing is performed. If it is an update process, in step S708, the internal data is rewritten as desired by the user, and in step S709, the host 101 is requested to update the database with the rewritten data, and the process waits until it ends. The update here is not only rewriting the data to a new value, but also broadly including adding and deleting the data.

The data reference / update processing is performed by the above procedure. FIG. 5 shows that the time set in the timer started in step S705 of FIG.
It is a flowchart which shows the procedure of a process when 01 is notified of it. First, in step S801, to read the update file stored in the host 101,
It issues a request to the host 101 and waits for a response. When the response from the host is received, its contents are tested in step S802 to check whether the received update file includes the data read by the terminal as internal data. This collation is performed using an identifier for uniquely identifying each data in the database. In this embodiment,
A unique number is given to each data record as an ID number to identify the data.

As a result of the collation, if there is no corresponding data in the update file, the value of the process is set again in the timer in step S804 and the process is started, and the process before the expiration of the timer is continued. On the other hand, if there is applicable data as a result of the collation in step S802, in step S803,
Update the internal data with the data in the update file.
This update has a procedure as shown in FIG. 6, for example. First, in step S601, the top update data of the read update file is read. Next, in step S602, it is tested whether the update data of the update file has ended.
This can be determined from the size of the received update file.

In step S603, step S601
Test whether the update data read by is stored in the internal data of the terminal as a result of retrieval. If not stored, the process proceeds to step S604, the next update data is read, and the process returns to step S602. If update data exists in the internal data, it is tested in step S605 whether the update data is data for an add operation. If it is an addition operation, it should be read out by the search, so in step S606, the update data is added to the internal data.

Next, in step S607, it is tested whether or not the update data is data for a delete operation, and if so, the data that is deleted and cannot be read is the data in the figure. Therefore, in step S609, the update data is internally written. Delete from data. On the other hand, if it is neither added nor deleted,
It is determined that this is a replacement operation of existing data, and in step S608, the updated data is updated in step S of FIG.
It is tested whether or not the search conditions set and stored in 701 are met. If they match, the updated data is also the target to be read out by the search, so step S6
At 10, the internal data is replaced with the updated data.

If they do not match, the updated data is the data that should not be read by the search, so the updated data is deleted from the internal data in step S609. The data read in the terminal is updated by the above procedure. After this step S803, in order to maintain consistency of the processing performed using the read data in response to the new data, step S803 is performed.
The process proceeds to step 705 and the process is performed again. However, with respect to the processing that does not impair the consistency due to the update, such as sorting, the necessary processing may be performed only for the data that is newly replaced / added. For example, in the case of sorting, new data is inserted in the already sorted data in the correct order.

It is desirable that the internal data be sorted using the ID as a key in order to facilitate the collation of the update file and the internal data and to facilitate the reference by the terminal. <Processing by Host> On the other hand, the host 101 performs processing according to various requests from the terminal. FIG. 7 shows the host 101
Is an update process for an update request from the terminal. Upon receiving the update request from the terminal, first, in step S701, the database is updated. Update here includes each operation of addition, deletion, and replacement. After this,
An operation ID number indicating the type of operation is added to the update data, and the update data is added to the update file in step S703. The operation ID number is as shown in FIG.
This is the data added to determine the type of update data in step S605 or S607. For example,
It is a unique value for each operation such as "A" for addition, "B" for deletion, and "C" for replacement.

It should be noted that the size of the update file may be such that, when one terminal is focused on, the update data for the time interval at which the terminal refers to the update file can be recorded. Assuming that the reference time intervals of the respective terminals are the same, a time shift of half the reference time interval is expected at the timing when a plurality of terminals refer to the update file. Therefore, the size of the update file needs to be the size of the amount of data that is updated at a time that is twice the reference time interval. For example, if the update file of this size is divided into two and the two update files are alternately used for each reference time interval of the terminal, it is possible to notify the terminal of the record of all the updates.

According to the above procedure, the terminal updates the internal data by referring to the update record at predetermined time intervals while accessing the database, so that the latest data can always be used. Also, when updating, the database is updated using new data after being updated by other terminals, so even if data updates from multiple terminals collide, one of the update records will be ignored. There is no such thing. Therefore, it is not necessary to perform exclusive control on the data to be updated. <Example of Access> Next, the update process will be described using specific data.

FIG. 8 shows an example of processing for searching the database of the host 101 from the terminal 102 and displaying it. From the left of the figure, the contents of the host database, the contents of the host update file, the internal data read into the terminal, and the contents displayed on the display 304 of the terminal are shown. This is the same in FIG. 9. In FIG. 8, the operator of the terminal searches the database by giving "the mnemonic does not include" E "" as a search condition, and instructs the terminal to "display the obtained data sorted by mnemonic". Is given to. Therefore, the internal data obtained at the terminal as a result of the search is "ABC", "AB"
There are three types, "D" and "BCD", which are sorted and displayed.

Here, the database is updated from another terminal 103. The contents of communication are the data "ABD" and "CB".
As a result, each data changes as shown in Fig. 9. As the update file, the ID number "C" indicating that the replaced data is a replacement
And has been updated.

When a predetermined time has elapsed after searching the database, the terminal 102 issues a request to read the update file to the host and obtains the update file. Its data ID ”
002 "indicates that the update data is included in the internal data. Further, the update data" CBD "matches the first search condition" does not include mnemonic "E"". Therefore, the internal data "ABD" is changed to "update data C".
It is replaced with BD "and the subsequent processing is performed, that is," the obtained data is sorted by mnemonic and displayed ".

As described above, according to the data access control in the database system of the present embodiment, the data referred to by the user always coincides with the actual database, so that a plurality of users refer to the same data at the same time. In this case, it is guaranteed that the same data is referred to without any time lag regardless of whether or not the data is updated. That is, the result obtained by referring to the database at an arbitrary time point is the same as the result obtained by referring to the database at the same time. Further, since the result of sorting / selection or the like can be saved by the difference calculation regardless of the data update of another user, it is not necessary to perform sorting / selection again.

[0025]

As described above, the data access control method according to the present invention has an effect that the data to be referred to is always the latest and the same data can be updated simultaneously by a plurality of users.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a database system according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a host computer according to an embodiment of the present invention.

FIG. 3 is a block diagram illustrating a configuration of a terminal device according to an embodiment.

FIG. 4 is a flowchart showing a procedure of data reference / update by the terminal device of the embodiment.

FIG. 5 is a flowchart showing a procedure of data reference / update by the terminal device of the embodiment.

FIG. 6 is a flowchart showing a procedure of data reference / update by the terminal device of the embodiment.

FIG. 7 is a flowchart showing a procedure for updating data by the host according to the embodiment.

FIG. 8 is a diagram showing a specific example of data search by the database system of the embodiment.

FIG. 9 is a diagram showing a specific example of data search by the database system of the embodiment.

[Explanation of symbols]

 101 host 102 terminal device 103 terminal device 104 terminal device 105 communication cable

Claims (4)

[Claims] 1. A data access control method for controlling access to data by a plurality of users, comprising a recording step of recording a data update history, a data reading step of reading desired data, and a data recording step performed by the recording step. Data access control comprising: an update history reading step for reading the updated update history; and an updating step for updating the data read by the data reading step based on the update history read by the history reading step. Method. 2. The update history reading step reads the update history every predetermined time.
The described data access control method. 3. The reading step reads data that matches a desired search condition, and the updating unit updates the data based on the update history and the search condition. Data access control method. 4. The method further comprising a processing step of performing desired processing by using the data read by the data reading means as an input, and performing the processing step again by inputting the data updated by the updating step. The data access control method according to claim 1.