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A simple data set consists of a single column of values. This appears in the form of a list. The collection of values in such a univariate data set is not a typical set (ordered list) in the mathematical sense. Rather they are called as a multiset.The values contained in a data set may be numbers or nominal data. Web browser or operating system, wants to access a datum, presumably in the permanent storage, it first checks the cache. If it finds an entry there with a tag matching that of the desired datum, it uses the datum in the entry instead of the datum in the backing store. This process is known as cache hit. On the other hand, if it does not find the datum with the desired tag, the situation is known as a cache miss. A hit ratio is the percentage of data accesses that result in cache hits.The numbers can be real numbers or integers. However, for a given variable, the values will be of the same kind. There may be a missing value for a corresponding variable, which may be indicated in a different way.