Annex B (informative) — Model Drawing Philosophy

B.1 Introduction

Several drawing formats used in this standard.

This annex discusses:

  • Model representation (Entity-Relationship Diagrams)
  • Step and transition for State-Based Control
  • Step and transition for Sequence-Based Control

Purpose:

  • Consistent notation
  • Clear communication
  • Standard symbols
  • Reduced ambiguity

B.2 Model Representation

Model drawings based on:

Entity-Relationship Diagram (ERD)

Modeling formats discussed provide:

Non-rigorous method of portraying:

  • Information
  • Relationships
  • Structure
  • Connections

Important notes:

Not intended to:

  • Recommend analysis methodology
  • Imply specific approach
  • Have figures supersede text

Figures support text - text is authoritative!

B.3 Basic Symbols

The following symbols are used:

Figure B.1 – Basic Symbols

Symbol meanings:

Rectangle:

Entity or model

Diamond:

Relationship

Lines:

Connections

Symbols at line ends:

Cardinality (how many)

These symbols demonstrated in following sections.

B.4 Relationship Examples

B.4.1 One to One

The following figure represents one to one relationship:

Figure B.2 – One-to-One Relationship

What this means:

  • One entity on left
  • Related to exactly one entity on right
  • 1:1 relationship

Example:

One Physical Model ↔︎ One Procedure Specification Model

B.4.2 Zero or One Occurrence

The following figure represents zero or one occurrence:

Figure B.3 – Zero or One Occurrence

What this means:

  • Entity on left
  • May have zero OR one related entity on right
  • Optional relationship

Example:

Procedure may have zero or one detailed design specification (optional documentation).

B.4.3 One or More Occurrences

The following figure represents one or more occurrences:

Figure B.4 – One or More Occurrences

What this means:

  • Entity on left
  • Must have at least one related entity on right
  • Could have more than one
  • Required relationship with multiple possible

Example:

Automated Procedure must have one or more steps.

B.4.4 Zero, One or More Occurrences

The following figure represents zero, one or more occurrences:

Figure B.5 – Zero, One or More Occurrences

What this means:

  • Entity on left
  • May have zero, one, or many related entities on right
  • Completely optional
  • If present, can be multiple

Example:

Procedure may have zero, one, or many operator prompts (completely flexible).

B.4.5 One to Many

The following figure represents one to many occurrence of same module:

Figure B.6 – One-to-Many Occurrence of the Same Module

What this means:

  • One entity at top
  • Related to many entities below
  • Parent-child relationship
  • Hierarchical structure

Example:

One Unit Procedure contains many Equipment Procedures.

B.5 Model Types

Models shown as rectangles in all drawings.

Three types with different shapes:

Figure B.7 – Model Types and Their Shapes

Physical Model:

  • Rectangle (standard)
  • Represents physical equipment hierarchy
  • Devices, equipment, units, areas, plants

Specification Model:

  • Rectangle with one corner cut
  • Represents functional specifications
  • Platform-independent
  • Requirements and design intent

Implementation Model:

  • Round corner rectangle
  • Represents actual implementation
  • Platform-dependent
  • Coded modules

Different shapes = instant visual identification of model type!

B.6 Step and Transition for State-Based Control

The step and transition diagram for state-based control consists of:

B.6.1 Components

Step:

Shown as solid rectangle shape with step name inside.

Transition:

Shown in different formats:

  • Line connecting two steps (simple)
  • Lines and transition symbols (thick line) connecting two steps
  • Lines and round rectangle connecting two steps

Figure B.8 – Step and Transition Components

Step = what procedure is doing

Transition = condition to move to next step

B.6.2 Transition Modes

The transition can be shown in three different modes:

Figure B.9 – Transition Modes

Automatic:

  • Solid line
  • Transition happens automatically
  • No operator action needed

Manual:

  • Dotted line
  • Requires operator action
  • Operator initiates transition

Automatic/Manual:

  • Solid line with character “M”
  • Can happen either way
  • Operator can choose

Mode indicates level of operator involvement!

B.6.3 Mode Examples

The following figure demonstrates different modes:

Figure B.10 – Examples of Transition Modes

This diagram shows:

  • Multiple steps
  • Various transition types
  • Automatic transitions (solid lines)
  • Manual transitions (dotted lines)
  • Combined transitions (solid + M)

Real procedure example:

  • Heat → Automatic transition → Check Temperature
  • Check Temperature → Manual transition (operator decides) → Establish Reflux
  • Establish Reflux → Automatic/Manual transition → Normal Operation

Flexibility in automation level!

B.7 Step and Transition for Sequence-Based Control

In sequence-based control (similar to ISA-88 implementation):

There may be more than one step being active as shown below:

Figure B.12 – More than One Active Step in Sequence-Based Control

Key difference from State-Based:

State-Based Control:

  • Only one step active at a time
  • Serial execution
  • One thing at a time

Sequence-Based Control:

  • Multiple steps can be active simultaneously
  • Parallel execution
  • Multiple things at once

Example:

Parallel steps:

  • Heat tower (Step 1)
  • Fill buffer tank (Step 2) - SIMULTANEOUSLY
  • Monitor alarms (Step 3) - SIMULTANEOUSLY

All three active at same time!

Synchronization points:

  • Steps come back together
  • Wait for all to complete
  • Continue when all done

More complex but more flexible!