Objects and Values

There are two primary types of entities that comprise and are manipulated by Analytica models: Objects and Values. Understanding this simple distinction can help you understand several of the other language features and concepts in Analytica.

An Analytica value is essentially data. A value can be an intelligent array or an atomic value. An intelligent array is a collection of atomic value. The result of any calculation is a value. Anything passed as a parameter to a function or an operator is a value.

An Analytica object is an entity that has a class, a name, and set of attribute values. Each attribute value associates a value with a particular attribute, so that an object typically contains several values. For example, a (global) variable, which you often see as a rounded rectangle on an influence diagram, is an object that usually has values associated with the attributes Title, Description, Units, Definition, (mid-)Value, ProbValue (aka. Sample value), Domain and Check among others. In addition, Class and Identifier are also attributes.

Values

Value can take subdivided into these subtypes (among others)

• Atomic values
  • Numbers
  • Text
  • The «null» value
  • Handles
  • References
• Arrays
  • Lists

Atomic values form the cells of arrays, but they may also stand by themselves as values. For example, the result of 1+2 is the atomic value 3, which is not an array. The Title attribute of any object is an atomic text value. We use the term "atomic value", or just "atom", to distinguish from an array.

A array is a rectangular (or hyper-rectangular) collection of "cells", where each cell contains an atomic value. Arrays can have between 1 and 24 dimensions (or between 1 and 15 dimensions in 32-bit Analytica). Each dimension is associated with an index, with each dimension associated with a different index. An index, by the way is an object. There is one exception -- during computation, one dimension of an array can contain an implicit index. A list is a 1-D array where the only dimensions is an implicit dimension. Lists are used to define indexes.