1. A method for accessing and retrieving data from different data sources at runtime of an interpreted language script, said method comprising the steps of: providing a data definition document that includes one or more tags, wherein the one or more tags are configured for accessing and retrieving data from a designated data source; including the one or more tags in the interpreted language script to represent one or more data elements whose data value is to be retrieved; and interpreting the interpreted language script using script interpreting engine; detecting any of the one or more tags in the interpreted language script and upon detecting one of the tags: (1) delegating accessing and retrieving data from a designated data source to a data lookup engine; (2) accessing the data definition document using the data lookup engine; (3) executing the one or more tags included in the data definition document; and (4) returning a retrieved data value to the script interpreting engine from the designated data source.