Robust data loading poses a challenge in database systems because the input data are often dirty. In many cases, an input record may have several missing values and some records could be contaminated (i.e., with some data values out of range or of a different data type than expected). Work out a step-by-step data cleaning and loading procedure so that the erroneous data will be marked and contaminated data will not be mistakenly inserted into the database during data loading. (references please)