What are Trends

Getting trends is storing values of selected variables with a time stamp into memory and on disk of the computer (this is done by the PmTrend object). These values can be consequentially displayed in a graphic or table form as time flows of these variables (this is done by the TrendsView graphic ActiveX item) or kept for the next analyses.

The PmTrend object serves for both historical (on disk) and memory trends (only in computer memory). The trend server is the PROMOTIC application in which one or more PmTrend objects are used. Each PmTrend object represents a group on the trend server that is unambiguously identified by the Group ID identifier string.

For the detailed description of creating trends, see PROMOTIC Coursebook - chapter Trends. For the examples see Example of creating client/server trends.

- Client/server architecture.
- Server stores data on disk in the following formats: dBase, Access, PROMOTIC binary, MS SQL, MySQL, FireBird, Oracle.
- Backup system of storing on disk or into a recurrent file. The size (specified by time or number of lines) of one backup file and the number of these backup files is defined at the backup system. The oldest backup is deleted after the number of backups is reached and a new backup is created.
- "Caching" into memory on the server. Defined data sector is stored into memory in parallel in the process of storing on disk (historical trends). When processing current queries by the server, it needn't query data on disk. It is the substantial acceleration of data query transactions.
- Server can be a Web component and it can provide data into the Intranet/Internet in the XML and HTML format.
- Server can be asked (independently on a viewer) for a data set. At a data query it is possible to enter filter conditions that limit the asked data set. See for example the PmTrend.GetData method. This method also allows to statistically evaluate the data (average, minimum, maximum, sum, count).
- The server data can be exported (browser independently) into a text file saved on the computers hard disk, using for example the *.csv format. See method: PmTrend.SaveToFile.
- The trend server supports the change-optimalized data storage, i.e. the values can be stored only after defined changes occured. See: Enable saving of variables on change.
- Data stored by the server can be consequently edited backwards and error values can be corrected by the PmTrend.SetValueByTime method.
- Server (any PmTrend object) can read and evaluate data from databases created by the 3rd party in the "Read only (new records cannot be written)" mode by setting the Read only (new records cannot be written) option.
- It is possible to configure and set parameter prints on the server and the client by HTML pages. Pre-configured printer HTML pages are supplied with PROMOTIC and they can be arbitrary modified. It is possible to print, for example, by means of the TrendsView.SaveToHtm method either in a graphic or in table form.
- The trend server (PmTrend object) can change the data archive location dynamicaly on the na disc or connect to existing data archive using the PmTrend.Open, PmTrend.Close methods.
- Client (viewer) is the graphic ActiveX TrendsView object. It displays data in the graph or table form. The viewer can be located either in a panel of the PROMOTIC system or in the Internet Explorer. The viewer views data continuously and independently on how the backup files were created. Any 3rd party application (for example HTML pages) can be the client that will process data provided by the server for example into the Internet by Web services. The way of the view - the graphic view in the form of 2D or 3D view with a potential for multi-level color diversity of marginal values or the table view with a potential for color diversity of marginal values. See: TrendsView.ViewMode.
- Interactive viewing the variable flows by the mouse - scrolling and zooming by dragging the mouse.
- Viewer can serve as a stand-alone viewer of 2-dimensional function y=f(x) without the necessity to add the viewer to some data source - the trend server. Thus the independent variable needn't be only the time. The flow of this function is defined in a script form by the tvPoints object. See: Example of displaying mathematical functions by a trends viewer.
- Dynamic configuration of the viewer. Add, delete the variable flow, change the graphic appearance, etc. by pre-configured HTML pages on the runtime. See: TrendsView.DlgTrends and tvTrend.DlgProperties.
- In the viewer it is possible to create configuration files (XML format) where it is possible to store the current settings of the viewer. It goes first of all about saving the list of viewed variables and their configuration but it is possible even to save the graphic appearance of the viewer. By creating several such groups it is then possible very easy to switch the viewer between these groups and so to view flows of logically joint variables. See: Configuration trend files, TrendsView.SaveCfg and TrendsView.LoadCfg.
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