TAILIEUCHUNG - SQL PROGRAMMING STYLE- P29

SQL PROGRAMMING STYLE- P29:Im mot trying to teach you to program in SQL in this book. You might want to read that again. If that is what you wanted, there are better books. This ought to be the second book you buy, not the first. I assume that you already write SQL at some level and want to get better at it. If you want to learn SQL programming tricks, get a copy of my other book, SQL for Smarties (3rd edition, 2005). | Scale Conversion 77 Using Scales Absolute and ratio scales are also called extensive scales because they deal with quantities as opposed to the remaining scales which are intensive because they measure qualities. Quantities can be added and manipulated together whereas qualities cannot. Table describes the different types of scales and their attributes. -------- Table Scale properties Type of Scale Natural Ordering Natural Origin Functions Example Nominal No No No City names Atlanta Categorical No No No Species dog cat Absolute Yes Yes Yes Eggs dozen Ordinal Yes No No Preferences agree 1 to 5 scale Rank Yes Yes No Contests win place show Interval Yes No Yes Time hours minutes Ratio Yes Yes Yes Length meters Mass grams The origin for the absolute scale is numeric zero and the natural functions are simple arithmetic. However things are not always this simple. Temperature has an origin point at absolute zero and its natural functions average heat over mass. This is why you cannot defrost a refrigerator which is at 0 degrees Celsius by putting a chicken whose body temperature is 35 degrees Celsius inside of it. The chicken does not have enough mass relative to heat. However a bar of white-hot steel will do a nice job. Scale Conversion Scales can be put in a partial order based on the permissible transformations 78 CHAPTER 4 SCALES AND MEASUREMENTS An attribute might not fit exactly into any of these scales. For example you mix nominal and ordinal information in a single scale such as in questionnaires that have several nonresponse categories. It is common to have scales that mix ordinal and an interval scale by assuming the attribute is really a smooth monotone function. Subjective rating scales strongly agree agree . . . strongly disagree have no equally spaced intervals between the ratings but there are statistical techniques to ensure that the difference between two intervals is within certain limits. A binary variable is at least an interval .

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