ProSoft Technology ProSoft i-View - Manual (Page 46)

Data Source Files ProSoft i-View ♦ Mobile Process Monitoring and Control Application
User Manual Version 2.0.2
Page 46 of 106 ProSoft Technology, Inc.
September 29, 2011
3.1.15 Expressions
Expressions are allowed on several attributes and provide an advanced way to customize
various aspects of the interface and behavior of ProSoft i-View projects.
Expressions allow for combining tags with operators to produce custom results. Tags are
referenced in expressions by using their names as entered in Column A. There are also
several system variables that can be used for special uses.
Event Driven Architecture
Expressions in ProSoft i-View are stored in a compiled form and are executed by an
event-driven engine. The execution engine keeps expression reference information in a
way that value changes trigger expression evaluation. The engine is not endlessly
executing 'for' loops but only change events.
Expressions keep references to referring expressions to create a tree like network where
all expressions have links to other expressions. When a PLC tag changes, or an user
interacts on a control, a change event is triggered. This event, that occurs at some point
in the expressions network, is propagated through the relevant links to reach only the
expressions that need to know about it, generally only a few.
The result is that expressions execution time is basically independent of project sizes or
the total number of expressions defined in projects. The Event Driven Architecture is
specially suitable for running ProSoft i-View in the constrained environment of a mobile
device and still be able to support a very large number of tags with no noticeable
performance penalties.