Chapter 17. Data Quality
As early as the 1960s, there was an expression in computing that most people in the field agreed was true: “Garbage in, garbage out.” (It was abbreviated GIGO and was pronounced “guy-go.”) We worried about the effect of the quality of input data on the output of our programs. In the intervening years, during the rise of databases, GIGO was largely forgotten. Today, however, with some data warehouses approaching a petabyte of data, the quality of that data has become extremely important once again.
Exactly what do we mean by “data quality”? To be useful, the data in a database must be accurate, timely, and available when needed. Data quality ensures the accuracy and timeliness of data and, as you will see, it is much easier ...

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