ROW_ID is a standard SAP Structure so does not store data like a database table does. It can be used to define the fields of other actual tables or to process "Material Quantity Calculation: Line Identification" Information within sap ABAP programs. This is done by declaring abap internal tables, work areas or database tables based on this Structure. These can then be used to store and process the required data appropriately. i.e. DATA: wa_ROW_ID TYPE ROW_ID.
The ROW_ID table consists of various fields, each holding specific information or linking keys about Material Quantity Calculation: Line Identification data available in SAP. These include KNOTEN (Character field, 8 characters long), STLTY (BOM category), STLNR (Bill of material), STLAL (Alternative BOM)... See below for full list along with technical details, documentation, text table, check tables, foreign key relationships, conversion routines, relevant tcodes and example ABAP select code etc. .