Why ls Data Dirty? incomplete data may come from Not applicable"data value when collected Different considerations between the time when the data was collected and when it is analyzed Human/hardware/software problems Noisy data(incorrect values) may come from Faulty data collection instruments Human or computer error at data entry Errors in data transmission Inconsistent data may come from Different data sources Functional dependency violation(e. g. modify some linked data) Duplicate records also need data cleaning3 Why Is Data Dirty? ◼ Incomplete data may come from ◼ “Not applicable” data value when collected ◼ Different considerations between the time when the data was collected and when it is analyzed. ◼ Human/hardware/software problems ◼ Noisy data (incorrect values) may come from ◼ Faulty data collection instruments ◼ Human or computer error at data entry ◼ Errors in data transmission ◼ Inconsistent data may come from ◼ Different data sources ◼ Functional dependency violation (e.g., modify some linked data) ◼ Duplicate records also need data cleaning