4.2 Components in the expression

The four key components in mcal includes constants, item value, operator, and function. In every component, it is important for user to understand the application of data type. mcal handles CSV text data, all values are expressed as character strings, user can define the data type to be handled in mcal. There are five string types in mcal, they are string type ( $str$ ), numeric type ( $num$ ), date type ( $date$ ), time type ( $time$ ), boolean type ( $bool$ ). The following sessions illustrates how each component constitutes to the expression and how to treat the data types.