Setting Stream and Session Parameters
Parameters can be defined for use in CLEM expressions and in scripting. They are, in effect, user-defined variables that are saved and persisted with the current stream, session, or SuperNode and can be accessed from the user interface as well as through scripting. If you save a stream, for example, any parameters set for that stream are also saved. (This distinguishes them from local script variables, which can be used only in the script in which they are declared.) Parameters are often used in scripting to control the behavior of the script, by providing information about fields and values that do not need to be hard coded in the script.
The scope of a parameter depends on where it is set:
- Stream parameters can be set in a stream script or in the stream properties dialog box, and they are available to all nodes in the stream. They are displayed on the Parameters list in the Expression Builder.
- Session parameters can be set in a stand-alone script or in the session parameters dialog box. They are available to all streams used in the current session (all streams listed on the Streams tab in the managers pane).
Parameters can also be set for SuperNodes, in which case they are visible only to nodes encapsulated within that SuperNode.
To Set Stream and Session Parameters through the User Interface
- To set stream parameters, on the main menu, click:
- To set session parameters, click Set Session Parameters on the Tools menu.
Prompt?. Check this box if you want the user to be prompted at runtime to enter a value for this parameter.
Name. Parameter names are listed here. You can create a new parameter by entering a name in this field. For example, to create a parameter for the minimum temperature, you could type minvalue. Do not include the $P- prefix that denotes a parameter in CLEM expressions. This name is also used for display in the CLEM Expression Builder.
Long name. Lists the descriptive name for each parameter created.
Storage. Select a storage type from the list. Storage indicates how the data values are stored in the parameter. For example, when working with values containing leading zeros that you want to preserve (such as 008), you should select String as the storage type. Otherwise, the zeros will be stripped from the value. Available storage types are string, integer, real, time, date, and timestamp. For date parameters, note that values must be specified using ISO standard notation as shown in the next paragraph.
Value. Lists the current value for each parameter. Adjust the parameter as required. Note that for date parameters, values must be specified in ISO standard notation (that is, YYYY-MM-DD). Dates specified in other formats are not accepted.
Type (optional). If you plan to deploy the stream to an external application, select a measurement level from the list. Otherwise, it is advisable to leave the Type column as is. If you want to specify value constraints for the parameter, such as upper and lower bounds for a numeric range, select Specify from the list.
Note that long name, storage, and type options can be set for parameters through the user interface only. These options cannot be set using scripts.
Click the arrows at the right to move the selected parameter further up or down the list of available parameters. Use the delete button (marked with an X) to remove the selected parameter.