The project's session is expanded tree of the project for direct it execution, which includes an individual task of hierarchical the widget's procedures execution. For each project can be opened many sessions. The end-user visual interface forming performs by the visualizers from data of the project's session, after the session creation by the request.

Between widgets at the different levels of hierarchy complex inheritance relations are arranged, which are defined by the possibility of using some widgets by other ones, beginning with the library widget, and finishing with the widget to the session. To clarify these features of the interaction in Figure comprehensive map of "uses" inheritance is shown.



At the session level widget contains a object of values of calculation procedure. This object is initiated and used in the case of presence of the calculation procedure. At the time of the initialization the list of parameters of the procedure is created and a compilation of procedure is performed with these parameters in the module, implementing the selected programming language and encoded with the full name of the widget. A compiled function is connected to the object of values of the calculation procedure. Further the calculation is performed with the frequency of the session.

Calculation and processing of the widget on the whole runs in the following sequence:

• the events, which are available at the time of computation, are selected from the attribute "event" of the widget;
• events are loaded into the parameter "event" of the object of computation;
• values of the input connections are loaded into the object of calculation;
• values of special variables are loaded into the computation object (f_frq, f_start and f_stop);
• values of selected parameters of the widget are loaded into the object of computation;
• computation;
• uploading of the computation object's values to the selected parameters of the widget;
• uploading of the event from the parameter "event" of the computation object;
• processing the events and transfer the unprocessed events at the level above.

The objects of the session of the project inherit from an abstract object "Widget" and use the appropriate objects of the project. Thus, the session ("Session") uses the project ("Project") and forms expand tree on its basis. Project page "Page" is directly used by the session page "SessPage". The remaining objects ("SessWdg") are deployed in accordance with the hierarchy of page elements (Fig.3.1.2).

In addition to the standard properties of an abstract widget ("Widget") elements of the pages of session themselves get the following properties: storage of the object of values of computational procedure, calculation of the procedures and mechanism for processing of the events. Pages of the session, in addition, contain a container of the following by the hierarchy pages. The session generally is computed with the frequency and in the consistency:

• "Page of the top level" -> "Page of the lower level"
• "Widget of the lower level" -> "Widget of the top level"

This policy allows you to circumvention the pages in accordance with the hierarchy, and to rise on the top during the one iteration for the widget events.

Sessions at the level of the control interface of OpenSCADA supports multi-language depended from values of the generic attributes "lang" and next "user" and which visualizer can set in proper way of self language. This function enabled for dynamic messages translation of OpenSCADA.