Introduction › Concepts and Facilities › Mapping Services › Maps and Mapped Data Objects

Maps and Mapped Data Objects

Mapping Services provides NCL with a logical view of data, while removing from NCL the requirement to understand the physical representation of data. It does this by interposing a map that is used to interpret the data. A map contains the definition of the logical components of a complex data structure, as well as the data’s physical representation.

A complex data structure is processed by NCL as a Mapped Data Object (MDO). The NCL procedure can connect an MDO to a map. Only through the map can the NCL procedure access the logical components of the MDO. Once the map connection is made, the NCL procedure can reference the logical entities contained within the MDO by their symbolic names defined within the map.

Each time NCL references a symbolic name, Mapping Services locates the definition within the map, determines how the component is organized, and with a knowledge of the physical representation, navigates the data structure to access the logical data items.

Using this technique, only the system need be aware, through definitions contained within the map, of the actual representation of the data. The NCL programmer, and the procedure itself, need only understand and reference the logical data components.

By modifying the map alone, it is possible to alter the underlying physical data definitions as managed by the Mapping Services facility, without having to change any NCL code.