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Chapter 5

Describes how to represent values and types by using typed attributes, variables and parameters, lists and arrays, nested data structures, and external data.

Introduction

Summary of Representing Values and Types

Using Attributes to Represent Value Types

Hierarchy of Data Types

Using Indexed Attributes

Guidelines for Declaring Typed Attributes

Use Strong Typing

Avoid Declaring Attributes with the Item-or-value Data Type

Enumerate Symbolic Values

Use Truth Values for Two Alternative Symbolic Values

Use Indexed Attributes to Access Objects Based on Attribute Value

Always Declare an Attribute for Setpoints, Limits, and Constants

Using Variables and Parameters to Represent Historical Data

Variable and Parameter Class Hierarchy

Creating a Subclass of Variable or Parameter

Declaring an Attribute that Contains a Variable or Parameter

Comparison Between Typed Attributes, Parameters, and Variables

Guidelines for Using Typed Attributes, Parameters, and Variables

Use Typed Attributes Whenever Possible

Use Parameters for Simple Histories

Use Variables for More Complex Histories

Choose the Most Efficient Data Structure

Choose the Most Restrictive Data Type

Try to Avoid Time-Based History Specifications

Using Lists and Arrays to Represent Data Series

List and Array Class Hierarchy

Creating a Subclass of List or Array

Declaring an Attribute that Contains a List or Array

Comparison Between Lists and Arrays

Guidelines for Using Lists

Use Lists for Fast Insertion and Removal

Choose the Most Restrictive Data Type

Guidelines for Using Arrays

Use Arrays for Fast Access to Elements by Index

Always Change Array Elements, Never Conclude

Beware of Manipulating Array Elements

Choose the Most Restrictive Data Type

Use Stability Declarations for Value Array Subclasses

Use Native Arrays in Performance-Sensitive Code

Use Casting When Binding Array Subclasses to Local Variables

Using Structures and Sequences to Represent Composite Data

Accessing System-Defined Attributes

Comparison Between Structures and Items

Comparison Between Sequences and Lists

Guidelines for Creating Composite Data Structures

Use Structures to Create Items with Dynamic, Nested Attribute Values

Use Sequences to Create Nested Lists

Using Structures to Represent Attribute-Value Pairs

Creating and Accessing a Structure

Accessing Values of a Structure

Using Sequences to Represent Nested Data Structures

Creating and Accessing a Sequence

Accessing Values of a Sequence

Using Variables to Represent External or Simulated Data

Creating Variables that Obtain Values from External Data Sources

Creating an External Variable

Specifying the Data Server

Specifying the Expiration Time

Specifying the Default Update Interval

Using Variables to Represent External or Simulated Data

Creating Variables that Obtain Values from Formulas

Creating Generic Formulas

Creating Specific Formulas

Causing Variables to Seek Data

Guidelines for Using Variables

Limit Data Seeking

Make Validity Intervals as Long as Possible

Do Not Embed External Variables in Subobjects

Setting the Priority of Data Service

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