Expression Engine Overview

The Expression Engine provides the capability for PcVue to calculate a value, using variables, functions and operators, without the need to use one of the programming languages. For example:

EXP(LOG(INLET.PRESSURE)/2)

Expressions can be used in the following contexts.

• To compute the value of a variable based on a combination of constant values and the value of other variables. Known as Expression On Variable.
• To compute a value for display in a mimic. Either by entering an expression directly in the variable field of an animation, or by creating an Expression Template.
• In the Application Architect for the purpose of differentiation by computing property values at generation time.
• In an add-on developed using the SvMgr toolkit. For example, the MQTT add-on makes extensive use of the Json function for message payload deserialization and mapping to variable properties (VTQ).
• In Data Export for computing Folder, Workbook, Template and Sheet names.
• In the mapping of Sql variables to define how variable properties and fields returned by Sql requests are linked together.

For ease of use, an Expression Editor is provided when configuring Expression On Variable, Expression Templates, in the Application Architect, in the Sql variables mapping and in the Data Export. The Expression Editor includes features such as keyword auto-completion. The available variables, functions and operators depend on the context in which the Expression Editor is used. See Using the expression editor for more information. Show picture