1. A non-transitory computer-readable recording medium that stores therein a computer program that causes a computer to read pieces of data that are distributed in databases that accept program codes that cause the computer to execute and return a query result as data that are identified in hierarchical structures, the program codes comprising: first computer readable program code defining a query including statements where two consecutive statements are separated by a comma and each statement has a data part followed by a series of operators that the first operator acts on the data part and yields a data result for the next operator to act on, and so on each operator yields a data result for the next operator to act on, and the series of operators causes the computer with act-on operations in the order according to the operators appearing in the series from left to right; second computer readable program code defining a data term that has a name, a property list that is of a fifth computer readable program code, and a child list that is of a third computer readable program code; the third computer readable program code defining a structure type that is an ordered list of items of the second computer readable program code; fourth computer readable program code defining an operator that has parameters of a data type of the second or third computer readable program code, which references a piece of data of the third computer readable program code and causes the computer to execute on its parameters; the fifth computer readable program code defining a property list that is a group of pairs with a first data element in a pair identified as a property name and a second data element in the pair identified as a property value, which allows set union, intersection operations with another property list yielding a new property list as an operation result; sixth computer readable program code defining a variable that is identified as a character string prefixed with an underscore, which represents a piece of data in a type of third computer readable program code; and seventh computer readable program code causing the computer to execute and return a query result as data that are identified in hierarchical structures.