1. A method for accessing and retrieving data from different data sources at runtime of an interpreted language script, said method comprising: executing a software application including an interpreted language script, the interpreted language script including a tag representing a data element whose data value is to be retrieved during execution of the software application; and during execution of the software application, executing the interpreted language script using a script interpreting engine; and detecting the tag in the interpreted language script, and upon detecting the tag: (1) delegating accessing and retrieving data from a data source to a data lookup engine; (2) accessing a definition of the detected tag from a library including the definitions of a plurality of tags using the data lookup engine, the definitions of the tags specifying manners of accessing and retrieving data from different data sources; (3) retrieving, from a designated one of the different data sources, the data value of the data element represented by the detected tag, the data value being retrieved according to the definition of the detected tag in the library; and (4) returning the retrieved data value to the script interpreting engine from the designated data source.