1. Create a new workspace. Add a schema reader and point it to your schema source.

2. Create a new Published Parameter with the name TO_KEEP and the prompt "Fields to Keep"

3. Connect the source schema feature to a ParameterFetcher. Set the Parameter Name to TO_KEEP and the Target Attribute to _to_keep.

4. Connect the ParameterFetcher to a PythonCaller. Set the Python symbol to keep_defs and add the following Python source code:

from pyfme import *

def keep_defs(feature):
    att_name_list = feature.getListAttribute('attribute{}.name')
    att_ntype_list = feature.getListAttribute('attribute{}.native_data_type')
    att_ftype_list = feature.getListAttribute('attribute{}.fme_data_type')
    keep_values = feature.getStringAttribute('_to_keep')
    keep_list = keep_values.split(',')
  
    if att_name_list != None:
        feature.removeListAttribute('attribute{}.name')
        feature.removeListAttribute('attribute{}.native_data_type')
        feature.removeListAttribute('attribute{}.fme_data_type')
        count = 0

        for i in range(len(att_name_list)):
            if (att_name_list[i] in keep_list):
                feature.setStringAttribute(('attribute{'+str(count)+'}.name'),att_name_list[i])
                feature.setStringAttribute(('attribute{'+str(count)+'}.native_data_type'),att_ntype_list[i])
                feature.setStringAttribute(('attribute{'+str(count)+'}.fme_data_type'),att_ftype_list[i])
                count = count + 1

            if (att_name_list[i] == 'fme_geometry{0}'):
                feature.setStringAttribute('fme_geometry{0}',att_ftype_list[i])
  
5. Connect the PythonCaller to an AttributeRemover and remove the attribute _to_keep.

6. Add an FFS writer and create an output feature called "schema". Connect the AttributeRemover to the schema output and save the workspace as a Custom Format with the name SCHEMASUBSET.

You can now add the format SCHEMASUBSET as a schema source in workspace resources. Only the attributes listed in the Fields to Keep parameter will be used to generate a dynamic schema.