When a new Service Request is created, the multi-level drop down list for Service Request subject is available.

Where do the value for those drop down list come from?

Here below is what I found via debugging:

1. get allowed category type from table CRMC_PROC_CATTYP based on transaction type:
   
   Two entries found in CRMC_PROC_CATTYP:
   
   These two entries are inserted here:
   

Then check for the given combination of Transaction type plus Catalog category, whether there is existing schema defined. The check is done by API CL_CRM_ML_CATEGORY_UTIL=>GET_ASPECT. I wrote a small report to check whether a schema is available for corresponding category: ```abap REPORT zdetermine_schema.

PARAMETERS: guid TYPE crmt_object_guid OBLIGATORY DEFAULT ‘6C0B84B75FAB1ED7BC85AA545271F98C’,
cat TYPE crmt_catalogtype OBLIGATORY DEFAULT ‘C’.

DATA: lv_guid TYPE crmt_object_guid.

lv_guid = guid.

DATA: lr_aspect TYPE REF TO if_crm_erms_catego_aspect,
ls_detail TYPE crmt_erms_cat_as_buf.

CALL METHOD cl_crm_ml_category_util=>get_aspect
EXPORTING
iv_ref_guid = lv_guid
iv_ref_kind = ‘A’
iv_profile_type = ‘A’
iv_catalog_type = cat
IMPORTING
er_aspect = lr_aspect.
IF lr_aspect IS BOUND.
lr_aspect->get_details( IMPORTING ev_asp = ls_detail ).
WRITE:/ ‘ASP id:’, ls_detail-asp-asp_id.
ELSE.
WRITE:/ ‘No detail data found’.
ENDIF.

In my example, no schema exists for category C:
<img src="https://user-images.githubusercontent.com/5669954/34657258-5a95c35a-f45f-11e7-9045-8b220d3c42d9.png">

<img src="https://user-images.githubusercontent.com/5669954/34657259-5ac4481a-f45f-11e7-8d18-db7883b7e918.png">
But a schema exists for type D:
<img src="https://user-images.githubusercontent.com/5669954/34657260-5af5e622-f45f-11e7-8df7-82c8af018893.png">

<img src="https://user-images.githubusercontent.com/5669954/34657261-5b2580b2-f45f-11e7-998c-e3a08a40fdc7.png">
the ASP ID YBP_SERVICE comes from here:
<img src="https://user-images.githubusercontent.com/5669954/34657262-5b53622a-f45f-11e7-8669-98a0b211fa8d.png">

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