@SantoshCLSA

Use Data Transforms when

• Setting properties
• Iterating over page lists / page groups
• Synchronously referencing Data Pages
• Calling Functions
• Calling Data Transforms

Use Activities when...

• Calling other Activities
• Iterating over value lists / value groups
• Asynchronously referencing Data Pages
• Implementing Services
• Implementing Background processing
• Implementing Declare Trigger rules
• Implementing Declare OnChange rules
• Implementing Data Page post-load processing
• General orchestration of procedural processing

An Activity is something different where of course you can call Property-Set method or call DataTransform as well but you do many other things. Like showing harnesses, calling service rules etc.  Activity also provides a way to execute Java code directly, that DT does not.  Activities are harder to maintain and not as easy to construct as other rules in Pega. We should not use an activity for calculations or property validations that we can implement as constraints rules or Declare Expression rules. Use of a declarative rule (rather than an activity) eliminates the need to control how and when an activity executes. A best practice is to use declarative processing rather than activities when feasible.

A data transform rule provides a purpose-built rule for easily transforming and mapping clipboard data without using activities. In general, the data transform defines how target data (properties, pages, etc) is mapped from and transformed by source data (properties, pages, etc). I would say the DataTransform is a bit like a Property-Set method in an Activity. Mainly used to set values on clipboard pages for example. For data manipulations, we can use a Data Transform instead of an activity.

While they share much helper code, e.g. for the generation of property sets and When conditionals, the two assemblers have very different implementations.  This difference was primarily necessitated by Data Transform's "dual step page" model.

Regards,

Tashika