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As per my knowledge:
Backward Chaining mode executes when the target property is referenced. Backward chaining is supported only for declare expressions.
A single declarative expression can monitor trigger events no matter where that expression is used in the application.
Declarative processing rules do not depend upon other rules, such as data transforms, activities, or user interface (UI) rules, to perform updates.
Backward chaining executes declare expression rules when a value is needed for a property, as opposed to when inputs change. For example, a value may be needed because a property’s value is referenced in an HTML stream for display.
Backward chaining applies to declare expressions rules with the Calculate Value field set to one of the following:
When used if no value present
When used, if property is missing
Procedural processing depends upon rules, such as data transforms, activities, or user interface (UI) rules, to instruct the application when to look for a trigger event.
For instance, to trigger updates to the order total, you add a data transform to a flow action. When a user enters values, nothing changes until the user submits the form.
The updates are not automatic.
The submit process triggers the data transform to perform the update.
In order to make the changes visible to users as they enter values, you must configure sections to use the data transform to refresh the fields.
Also, kindly check the below PDN link for more details about declarative expression and backward chaining.
Thank you so much for explaining this. Although I've few more doubts.
Below is an excerpt from the PDN, please can you explain the line in bold and underlined?
"Backward chaining in a declare expression means that a target property value is not automatically updated when other declare expressions in a network update their target values. An expression using backward chaining only updates its target property when the application references the property by name. A form, a decision table, or a data transform can reference the property. When the property is referenced, the expression goes back in the network to reference the source property or properties the expression needs to update its target."