Datahub transformation logic

I have few question relating to datahub and going to st new project with a customer.

I am trying to gain common concepts about datahub.

1. I saw the following config in default saperpproduct-raw-datahub-extension.xml. In the config i see 2 transformation logic defined. How are these 2 transformation calculated. Is the value calculated from first transformation inserted to second transformation and if this is not the case what is the logic behind 2 transformation ?

                    <transformations>
                        <transformation>
                            <rawSource>RawCLSMAS</rawSource>
                            <expression>E1KLAHM-CLASS</expression>
                        </transformation>
                        <transformation>
                            <rawSource>RawCLFMAS</rawSource>
                            <expression spel="true">#root.getField('E1OCLFM-MAFID')
                                        == 'K' ? #root.getField('E1OCLFM-OBJEK') : null</expression>
                        </transformation>
                    </transformations>
   
   

2. In the same xml file i see transformation defined as input from 2 different raw types : RawCHRMAS and RawCLSMAS. These 2 raw types might be loading from 2 different idocs. Hows does datahub calculates from which 2 RawCHRMAS and RawCLSMAS to pick up data from ?

                      <transformations>
                        <transformation>
                            <rawSource>RawCHRMAS</rawSource>
                            <expression>E1CABNM-ATNAM</expression>
                        </transformation>
                        <transformation>
                            <rawSource>RawCLSMAS</rawSource>
                            <expression>E1KLAHM-E1KSMLM-ATNAM</expression>
                        </transformation>
                    </transformations>
   
   
   

Thank you in advance.