Elements which are common to these three standards are identified as a “Common Core”. The value of the Common Core is to assist program authors to exchange declarative applications internationally using these standards. To allow the possibility of interaction between different interactive platforms, a common instruction set (see Recommendation ITU-R BT.1722-2 [10.14]) and a common application environment for digital interactive television services consisting of basic architecture of the environment, structure of execution engine and the structure of a presentation engine (see Recommendation ITU-R BT.1889 [10.15]) are additionally defined.