Creation of the scheme of data

It is obvious, that those actions which have been in detail described for the table of the Paper, it is necessary to do and for other information files: Agents, Portfolios, Applications. As a result we shall receive system of tables of database TfadeTest. We shall emphasize, system as data being them closely and are substantially connected among themselves. Really, the data who are being a floor the Code of the agent of the table Portfolios, should be coordinated as and to the size with the data who are being the same floor of the table of the Paper. Moreover, the logic of a considered problem demands, that, working with the information concerning a portfolio, we could address simultaneously to the data describing the current agent, etc.
The mechanism of the description of logic communications between tables in Access is realized in the form of the object named by the Scheme of data. To pass to its creation it is possible from the panel of tools a Database, accessible of the main window. The alternative variant of a call of the given mode is accessible through the menu Service> the Scheme of data. The kind which will be had with the scheme of data for the tables constructed on the previous steps, is presented on fig.

It would be desirable to pay attention once again of the reader that the choice of type of a paper is carried out from in advance predetermined list.

The interface of the task of communications between fields in the scheme is based on "dragging" (moving at the pressed left button of the mouse) the chosen field and its "imposing" on that field with which communication should be established. For linkage at once their several fields it is necessary to move at pressed key Ctrl. Allocate some types of communications between tables in the scheme. " One to one " (1:1) - in one table corresponds to one value of a field only one value of a field in another. " One to many " (1:много) - in one table corresponds to one value of a field some values in another.

The major problem which the scheme) allows to solve, maintenance of logic integrity of data in base is. So, in database TradeTest infringement of integrity can arise in case of removal from the table of the Paper of records on those papers about which there are records in tables Portfolios or Applications therefore in their structure there will be references to the "lost" codes. It is obvious, that it can be prevented if in cascade to remove both records from the table of the Paper, and record of the tables connected by it. Such effect in Access can be reached(achieved) due to the task of the certain properties for communication. That it to make, it is necessary to click the button of the mouse, being on a line of the scheme designating communication. After that there is the dialogue window intended for change of properties of communication. Apparently from fig., within the limits of a mode of maintenance of integrity of data it is possible to set on the chosen communication(connection) as cascade updating of values for the connected fields, and cascade removal of the connected records.

The author:Y.N.Antonov Is added: 18.06.2008