A data record is a collection of related fields or data elements. Record design is one of the fundamental problems of data management. A data record should include all the data elements that are essential to an application. In certain instances, however, a particular data element might be computed as needed on the basis of the other data elements stored in a record. In such cases, it is not really necessary to store this type of data element in a data record because its value can be computed readily as needed. This type of data element is called virtual data. For example, a payroll record might contain the following three data elements in addition to others: pay rate per hour hours worked gross pay In this case, gross pay would be a virtual data element. Gross pay could be computed as needed based on the pay rate per hour and hours worked data elements. Virtual data are an example of redundancy in data records. The elimination of virtual data has several advantages. One is to reduce the overall size of the data record and thus reduce the amount of storage space required. This would tend to reduce the total cost of storing a data record. Another advantage is that there are fewer data items in the data record that have to be maintained. This might lead to simpler application programs and would tend to reduce the possibility of having errors occur when the data record is modified. This becomes more important when a data element is contained in more than one data record. In such cases, a data element might be updated in one record but not in others. This results in inconsistent data in an information system.

Consider the following data record for a work-in-process application system: Work-in-process number Materials cost Direct labor cost Applied overhead cost Total cost Units started Units spoiled Good units in process

Which of these data items is (are) virtual data? What types of advantages might be gained if virtual data elements are removed from the work-in-process record? Explain

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