As of enhancement package 7, SP 06 for SAP ERP 6.0, in Material Master, you can maintain the Segmentation Structure and the Segmentation Strategy fields as mandatory or optional fields based on the settings maintained in Customizing activity Define Attributes of System Messages under  Logistics – General Material Master Basic Settings . In this Customizing activity, for application Area “SGT_01” and number 022, 030 and 084, maintain the system message category as W to set fields Segmentation Structure and Segmentation Strategy as optional or maintain E to set the Segmentation Structure and Segmentation Strategy fields as mandatory.