Adata set (or dataset) is a collection of data. In the case of tabular data, a data set corresponds to
one or more database tables, where every column of a table represents a particular variable, and
each row corresponds to a given record of the data set in question. The data set lists values for each
of the variables, such as the height and weight of an object, for each member of the data set. Each
value is known as a datum. Data sets can also consist of a collection of documents or files.
In the open data discipline, the data set is the unit to measure the information released in a public
open data repository. The European Open Data portal aggregates more than half a million data sets.
Some other issues (real-time data sources, non-relational data sets, etc.) increase the difficulty to
reach a consensus about it.
Properties
Several characteristics define a data set’s structure and properties. These include the number and
types of the attributes or variables, and various statistical measures applicable to them, such as
standard deviation and kurtosis.
The values may be numbers, such as real numbers or integers, for example representing a person’s
height in centimeters, but may also be nominal data (i.e., not consisting of numerical values), for
example representing a person’s ethnicity. More generally, values may be of any of the kinds
described as a level of measurement. For each variable, the values are normally all of the same
kind. However, there may also be missing values, which must be indicated in some way.
In statistics, data sets usually come from actual observations obtained by sampling a statistical
population, and each row corresponds to the observations on one element of that population. Data
sets may further be generated by algorithms for the purpose of testing certain kinds of software.
Some modern statistical analysis software such as SPSS still present their data in the classical data
set fashion. If data is missing or suspicious an imputation method may be used to complete a data