International standard IEC 61162-420 specifies the requirement for and basic components of the IEC 61162-4 series companion standards. These components are referred to as follows: a) PCS (PISCES companion standards) which contain the rules for the creation of companion standards. The generate principles underlying the PCS are described in clause 4. b) PCSDL (PCS description language). Part of the PCS is the definition of the syntax for the various types of companion standard documents that make them readable by computer tools. The PCSDL is described in clause 5. c) function block description. The function block description is a high level and graphical description of applications using the IEC 61162-4 series interfacec standard. The function block syntax is specified in clause 7. d) PFS (PISCES foundation specifications) which contain a framework for classification of applications adhering to the IEC 61162-4 standard. The PFS wil also provide a minimum level of interoperability between manufacturers' applications using this framework. The PFS is described in clause 6.