Why was TotalPopulation2001 automatically created as a parameter for the custom transformer while NeighborhoodArea was not?

Why was TotalPopulation2001 automatically created as a parameter for the custom transformer while NeighborhoodArea was not?

• A. Custom transformers can only have one input parameter.
• B. TotalPopulation2001 is an attribute used within the custom transformer from the input data, while NeighborhoodArea is calculated within the custom transformer.
• C. TotalPopulation2001 is an integer and NeighborhoodArea is a floating point number.
• D. We manually chose to expose only TotalPopulation2001 as a parameter when creating the custom transformer by setting the Attribute References parameter to Fix Manually (Advanced).

Answer: (B)

The thing being tested is how FME treats data that comes from the input versus data that is created inside a custom transformer. Attributes that exist on the incoming features and are used inside the transformer are exposed as parameters because they define what the transformer takes from the outside world. TotalPopulation2001 fits this: it’s an input attribute used by the transformer’s logic, so FME automatically creates a parameter for it at the transformer level so you can feed in or map that attribute when reusing the transformer. NeighborhoodArea, on the other hand, is produced entirely within the transformer as a derived value; it isn’t something that comes from the input data and needs to be supplied from outside. Therefore it isn’t automatically exposed as a parameter.

The thing being tested is how FME treats data that comes from the input versus data that is created inside a custom transformer. Attributes that exist on the incoming features and are used inside the transformer are exposed as parameters because they define what the transformer takes from the outside world. TotalPopulation2001 fits this: it’s an input attribute used by the transformer’s logic, so FME automatically creates a parameter for it at the transformer level so you can feed in or map that attribute when reusing the transformer. NeighborhoodArea, on the other hand, is produced entirely within the transformer as a derived value; it isn’t something that comes from the input data and needs to be supplied from outside. Therefore it isn’t automatically exposed as a parameter.