procedural model

A procedural model is a structured representation of how a process is executed over time, capturing the ordered sequence of operations, phases, and steps required to carry out a task or batch. In industrial and manufacturing environments, it commonly refers to the modeled logic that defines what to do, in what order, and under which conditions.

In the context of batch and process manufacturing

Within standards such as ISA-88 (S88), the procedural model describes the hierarchy and flow of activities needed to run a batch or other process. It is distinct from the physical equipment model and focuses on what actions are performed rather than what hardware executes them.

An S88-style procedural model typically includes:

• Procedures: High-level descriptions of how to make a product or execute a major process.
• Unit procedures: Segments of the process tied to a specific processing unit.
• Operations: Logical groupings of tasks within a unit procedure, such as charging, heating, or mixing.
• Phases: The smallest control-level actions, often directly implemented in a DCS, PLC, or batch engine.

These elements are organized to express the process logic, including start and end conditions, interlocks, transitions, and exception handling. In practice, the procedural model is implemented in control systems, batch management systems, or MES as recipes, workflows, or automated sequences.

Operational meaning

Operationally, a procedural model:

• Defines the execution flow for manufacturing a product, cleaning a system, or performing a changeover.
• Provides a common structure that can be mapped to different units or equipment via recipes and equipment models.
• Supports integration with MES, batch engines, and DCS/PLC logic by providing a clear hierarchy of steps.
• Can be used as a reference when creating electronic batch records, digital work instructions, or automated workflows.

In regulated environments, a well-defined procedural model helps maintain consistency of process execution, supports impact assessment when changes are made, and facilitates traceability of what was executed and when.

Common confusion

• Procedural model vs. equipment model: The equipment model describes the physical assets (units, modules, connections). The procedural model describes the process logic and sequence of actions. In S88, these are complementary but separate views.
• Procedural model vs. recipe: A recipe often uses the procedural model structure but also includes parameters, formulas, and other product-specific data. The procedural model is the generic framework for how actions are organized and executed.
• Procedural model vs. workflow diagram: Many tools show the procedural model as a workflow or flowchart, but the term usually implies a formally structured hierarchy (procedure, unit procedure, operation, phase) rather than an informal diagram.

Connection to the S88 standard

In the context of S88, the procedural model is one of the core models used to describe batch manufacturing. It provides a standardized way to break down and represent process logic so that recipes, control strategies, and MES/DCS/ERP integrations can be designed and discussed using a common language. S88 does not mandate specific software or hardware; instead, its procedural model is a conceptual framework that systems and plants may choose to implement.