NET/MASTER Network Control Language (NCL) Programmer's Guide

Components in Mapping Services Processing
Working With Mapping Services
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Components in
Mapping Services
Processing
There are three main components in Mapping Services processing. The components
are briefly discussed here and discussed in detail throughout this section.
Maps
Mapped data object (MDO) variables
NCL procedures
Maps describe the structure of MDO variables. MDO variables contain data. The data
in an MDO variable is accessed from NCL procedures using certain verbs.
Mapping Services provides a set of facilities that mediates between these three
components. This allows each component to exist as a separate and distinct entity in
NonStop NET/MASTER MS. It allows Mapping Services to transparently manage
data manipulation as the components interact during the execution of an NCL process.
Maps Fundamental to Mapping Services is the concept of a map. A map is a series of
definitions that, together, describe the entire structure of some item of data contained
in an MDO variable. Each definition describes a single structure or substructure
within a data item. Included in every definition is the following:
The unique symbolic name of the definition—this is part of the header of the
definition
The unique key value of the definition—this is part of the header of the definition
The unique symbolic name of every structure within the definition
The unique key of every structure within the definition
The unique symbolic name of every substructure within the definition
The unique key of every substructure within the definition
The position—or offset—at which every structure and substructure begins
The length—fixed or variable—of every structure and substructure
Mapping Services supports a map file that contains the definitions of all maps that
Mapping Services can use. The map file and the maps $MSG, $NCL, $SEC, and $SPI
are discussed in detail in Section 11, “Standard and User-Defined Maps.”
Mapped Data Object (MDO)
Variables
An MDO variable contains data that is structured in a way that Mapping Services can
understand using a map. All structures and substructures in an MDO variable have
names. NCL can use the names to locate data at a certain position in an MDO variable.
The main data structure in an MDO variable is called an element. Logical
substructures in an element are called groups and fields. Understanding map
definitions allows you to understand and interpret the structure of data in an MDO
variable. It allows you, during the execution of an NCL process, to locate and refer to
the data contained in elements, groups, and fields by name. Map definitions provide
the names you use to refer to elements, groups, and fields from an NCL process.
The structures and substructures in an MDO variable are discussed in detail later in
this section.