D2000 offers the option of scripting - writing user scripts in ESL (Event Script Language) and Java.
A script can exist:
- Within a D2000 Event Handler process as an Event object whose parent is the corresponding D2000 Event Handler process.
- As part of pictures (so-called Active pictures) launched in D2000 HI or D2000 Thin Client processes. Within an active picture, the ESL script is an integral part of it (i.e. it is part of an object of type Picture).
ESL scripts can use (similar to eval tags) extensive mathematical data processing (Value Types, System Constants, Object Value Attributes, Expressions, and Functions).
In addition, ESL scripts can also contain Actions that can mediate the functionality of other processes (e.g. DBManager) and can be divided into several groups:
- assignment actions
- action for accessing a database
- actions for handling error states
- control actions
- actions for communication with the operator
- archive manipulation actions
- actions for synchronization of script actions execution
- controlling alarms
- structure manipulation actions
- data container manipulation actions
- access right manipulation actions
- actions for manipulation with a list of objects
- other actions
One of the following types is specified in the Event configuration:
- Trigger event - the script is executed when a specified condition occurs - a value changes, a process alarm occurs on the trigger object, the required value limit occurs, and others.
- Server event - the script executes its initialization part (between BEGIN and END) after starting (by default after the start of the D2000 Event Handler process, or after it is started by the OPENEVENT action, or after its transition to the active instance state in redundant systems). Subsequently, it is possible to call the RPC procedures that the event server implements (by using the CALL action). Using the ON CHANGE action, the server event can be registered to be notified of a change in the value of any object - then the specified procedure is invoked.
Note: with the OPENEVENT action, the event server can be started not only on any D2000 Event Handler process but also on the D2000 HI process. In addition, it is possible to specify the instance of the server event and thus achieve multiple openings of the Server Event within the given process. - Client and server event - has similar properties to the Server event, but if it is opened by the OPENEVENT action on the D2000 HI process, then the client part of the script is run in the D2000 HI process and the server part of the script is run in the D2000 SES process (which by default is run on the server). Splitting the script into two parts enables both performance optimization and combining access to the client computer and the server.
- Unit event - such a script is a "library" that can be inserted into another event (or into a scheme) by the UNIT declaration and its PUBLIC procedures can be called by the CALL action.
