.
A meta-model for leveraging the ISA-88/95/106 standards
Jean Vieille
SyntropicFactory, Control Chain Group, Interaxys
j.vieille@syntropicfactory.com
Abstract. Considered together the ISA-88, 95 and 106 standards can be
intimidating and confusing due to their large, overlapping scope, their different
level of specialization and viewpoint. However their shared history, expert
community, and domain of interest makes them conceptually consistent. This
article proposes three simple but still expressive models to address the intended
use cases of these standards. They can be specialized in any of the models in
these standards providing a robust basis for an object oriented implementation.
They can be used independently of these standards to develop industry /
enterprise specific interoperability and functional design languages.
1. Introduction
The story began in 1990 with the ISA-88 « Batch control » standard that addresses
modular automation for flexible batch processes. It was followed by the ISA-95
« Enterprise – control systems integration » standard that deals with manufacturing
operations management (MOPM, MES) and interoperability. The latest ISA-106
“Procedural Automation for Continuous Process Operations” standard tackles
procedural control for continuous processes. These standards provide good
engineering practices for improving control design for industrial facilities. ISA-88 and
ISA-95 are respectively published as international standards IEC61512 and
ISO/IEC62264.
These standards share genetic concepts due to their consanguinity: many experts
have contributed in the three standardization committees, which originated in ISA88.
Though their viewpoint, terminology and abstraction level sensibly differ, the way
they handle structural and behavioural aspects is relatively consistent, allowing a
quite straightforward retro engineering of their implied meta-model.
The interest of extracting a common meta-model of these standards is two-fold:
- It allows understanding the respective scope of each standard and their
overlap.
- It makes easier to consider interoperability in the broader architectural
approach of enterprise transformation
Despite its technical and specialized content, this article may be of interest even for
people who are not fluent in the discussed standards, but who could appreciate that
the thousand pages of these standards can be summarized into 3 simple generic
models.
This short article does not develop extensively the derivation of the proposed metamodel into specific objects in the quoted standards. However, this meta-model has
been successfully experimented both in the context of leveraging the standards within
a small company that could not afford large consulting rates for implementing a
compliant approach for interoperability and for developing an open, “lean B2MML”
XML schema definition capable of handling any standard objects as well as company
specific concepts.
2. Short overview of the discussed standards
ISA-88: functional design for control
Le ISA-88 standard « Batch Control » defines concepts and terminology for the
design of automation of flexible batch facilities. It features the following aspects:
Modular automation design.
The standard enforces modular design and encourages object design by improving
the potential of reuse of automation objects. This leads to reduced engineering effort,
better knowledge management and more robust and evolvable applications
Industrial system flexibility.
Control is an integrated part of the facility that aims both at driving and at
constraining the number of its possible states. When the number of products or
services the facility has to deliver increases, the number of permitted states increases:
control becomes more involved, hence potentially more difficult to implement.
Flexibility expresses the ability of the facility to handle effectively the required
behavior for each expected outcome under variable internal or external conditions.
Control is for example challenged for delivering different products using different
equipment, or the same product using different equipment which is a root requirement
addressed by ISA-88.
Interoperability and Information.
ISA-88 provides a language (models and terminology, grammar and vocabulary)
that may be used to support interactions between process engineers, operators,
software vendors and system integrators. Data structures help for exchanging
information between applications and for contextualizing it in production databases.
Description and Industrialization of manufacturing processes.
ISA-88 proposes to formalize (1) the product making knowledge in terms of
physico-chemical transformations required to obtain a product with specified
characteristics, (2) the operations sequencing for making the product in a given
facility, and (3) a way to transform the neutral requirements (1) into executable
operating procedures (2)
Applications.
ISA-88 is first a reference for the functional design of automation applications.
Dedicated to flexible batch processes, it applies also to other manufacturing strategies
that are considered less constraining, problematic for control engineers.
ISA-88 keeps distant from technology and does not fundamentally require specific
features of DCS, PLC or SCADA/MES applications. However, It software vendors
propose many ISA-88 labelled solutions: design tools, batch managers, data
historians, and automation objects libraries.
ISA-95: MOM/MES and Interoperability
The ISA-95 standard defines data models for exchanging information between
manufacturing related applications (ERP, MES, SCADA, LIMS, MMS, WMS…) as
well as an activity framework for gathering requirements, designing functions,
urbanizing applications for supporting manufacturing operations.
Industrial system operations management.
The ISA-95 standard discusses extensively the information supports to operations
of industrial systems.
It is the de facto reference for managing the lifecycle of MES (Manufacturing
execution systems) / MOM (Manufacturing Operations Management) domain
functionalities (requirement, design urbanization, operations). It establishes a multidimensional map for managing related documentation and IT assets.
Interoperability.
ISA-95 define data structures for exchanging information between concerned
applications. The UML models are implemented as XML schemas in B2MML.
Applications.
Opposite to ISA-88, ISA-95 seeks neutrality toward manufacturing typology. It is
used as a functional design guide for information support to industrial systems and for
the design standard for interfaces between software applications.
Software vendors have sometime used the data models to design their application
persistence layer.
ISA-106: Procedural Automation for Continuous Process Operations
Launched in 2010, the ISA106 aims at promoting automated procedures in
continuous processes. These processes were mainly designed for mass production, but
are more and more required to be agile and optimized in terms of operations. The
recent emphasis to safety, throughput and quality led to this effort to best design the
automated starting, shutdown and exception handling of these facilities. The first
technical report proposes models and terminology partially inspired from ISA-88 and
ISA-95 to handle procedural design from requirement gathering to implementation.
3. Upper meta-model
The conceptualization of these standards builds on an upper level ontology that
combines elementary concepts within the space-time continuum broken down to
allow our World perception
The spatial view seeks to represent the observed system according to its shapes,
non-time related characteristics. It is static, meaning that the representation from the
observation at a given point in time is complete, or will not improve by a longer
observation, supposing that all relevant information is captured instantaneously. This
view can - will - evolve with time due to the continuous entropic (conflicts, “wear and
tears”, market lagging) and negentropic (engineering, organization) transformation of
the system and to its internal activities, ongoing interactions. However, this view does
not address the “movement”: it is a picture, not a movie.
The temporal view represents the behaviour of the system, its functioning: process
execution, event and subsequent activities that realize the system objectives.
Fig. . Upper meta-model
From a transversal perspective, the system representation builds from a primary
classification of the concepts involved in the existence and activity of the system:
matter, energy and information. This is yet another human way of braking down a
fundamental continuum in order to facilitate observation, understanding.
These abstract concepts are the building blocks for the representations in the spatial
and temporal views. Their meaning in the context of industrial systems as presented in
the ISA-88/95 and 106 standards can be easily reified:
Matter
• The input/outputs of the system as material, parts and products that are
bought, stored, elaborated, transformed, mixed, assembled, wasted, sold
• The components of the system as equipment that are installed, used,
maintained.
Energy
• The input/outputs of the system as energy bought, stored, consumed,
produced, wasted : fluids in closed circuits, electricity, combustibles
• Workforce involved in the system operation
Information
•
•
•
•
Knowledge accrued in the system: product and process know-how
Available documentation, used and created for or by the system operation,
Organisation,
Money available, spend, earned for and by the system operation, financial
aspects.
The meta-model is now complete. The right rectangle is the spatial view (the
system as it is observed in a specific point in time (the potentiality of the system); the
left pyramid is the time view (the kinetics of the system in action).
Fig. . Meta model for the study of ISA-88/95/106 standards
In the spatial view, elementary concepts – simple rectangles are considered under
their potentiality, regardless their involvement in operations.
In the time view, the pyramid represent the decisional / behavioural hierarchy of
the system in operation. The elementary concepts are arrowed: they are involved /
allocated to participated in the system activity (kinetics)
Space-time relationship.
The time and spatial view split is convenient to grasp the complexity of the
industrial system. In reality, they are tightly coupled because the living system keep
evolving with time. Unless the factory is stopped, under nitrogen conservation, the
spatial view is never up-to-date, it is only a representation snapshot if its state at a
specific point in time.
Fig. . Time-space coupling
In practice, the spatial view will describe the operating situations of the system in
action, identifying and describing the Processes that are part of the spatial view as a
knowledge asset, while the time view will consider the actual operation making use of
this knowledge.
4. Application to ISA standards
Applying this upper level meta-model to ISA-88, ISA-95 and ISA-106 consists in
specializing its generic concepts into each of these standards’ equivalent concepts.
This specialization takes into account the application domain and terminology of the
target standards. This is a “reification process” that derives abstract concepts into
more real, tangible ones.
Fig. . Meta-model reification
Elementary dimensions
The notions of matter and energy are not always clearly segregated. An electrical
consumption is with no much doubt considered as « pure energy”, but oil holds
obviously both dimensions. In reality, matter and energy, which are physically so
distinct, are always combined in tangible streams involving the combination of matter
and energy driven by machines and people.
To escape this ambiguity, the meta-model, as ISA-95 will not make a distinction
between both. Actually, from the enterprise viewpoint, matter and energy are of the
same nature: they are both inputs and outputs of their main value chain process, not
something that is part of them as a constituency asset. This does not preclude specific,
different management approaches to energy and matter streams.
ISA-95 defines the notion of Resource that takes matter and energy as one of them
along with people (person) and machines (role based equipment and physical asset)
that is understandable in the context of ISA-88 and ISA-106.
The de-correlated resource description always appears in the context of an activity:
in-formation gives form to something. In this original sense, information is at the
hearth of the transformation processes seeking a useful outcome: combining matter
and energy carelessly, without any knowledge will move the matter to an equal
entropy state at best while an organized, knowledge based process will produce a
more sophisticated process than the original combination of raw material.
This knowledge – information- is potential as long as it says in peoples and
computers memories, kinetics when it is in action. In the latter case, Information
sticks to the action it make productive by consuming energy unless it is useless or
entropic (can it be negative information?). Said another way: during an industrial
process transformation, the entropy of the blend of incorporated material decreases by
consuming energy, countering the so-called fated entropy increase of the universe.
For this reason, the information dimension appears under the more practical, less
open ended term Process applicable (with some possible confusing broadened
definition) to many elements of resources mobilization quoted with numerous terms
in the standards. For example, ISA-95 part 2 Product definition, Product segment,
Process segment, Production request … correspond to Processes in the meta model.
Spatial view
ISA standards focus on operational aspects of industrial systems, not on their
transformation. Resources are summarily addressed in the context of their
contribution to operations. Processes in ISA standards mainly address operational
activities to fulfil short-term market demand. ISA-88 par 3 goes further by tackling
product design to manufacturing. The spatial view is then limited to the description of
basis physical and informational entities involved in manufacturing.
Time view
From the studied standards, the time representation of the operating system can be
represented as a decisional, functional, behavioural hierarchy of four levels:
Operations Process Management for operational processes, Physical Process
Management and Physical Process Control for management and control of physical
equipment.
5. Spatial view - Resource
Resource meta-model
Only ISA-95 proposes a resource model. Other ISA standards address partial
aspects that are all more extensively defined in ISA-95.
ISA-TR106-01 does not offer a formal model; it only defines an alternate
terminology for ISA-88 concepts.
The resource meta-model presented in the following figure includes the following
sub-classes
- Type corresponds to the ISA-95 canonical model such as Equipment,
Material, Person and other specifics
- Role is a functional classification that allows to allocate resource
quantitatively and qualitatively without naming explicitly the corresponding
resources. It corresponds to ISA-95 class concept in equipment and
personnel resource, or material definition in material resource.
- Category is a complementary classification less constraining that roles to
further adapt resource definition to specific businesses. It corresponds to
ISA-95 Class concept in the material model.
- Context defines the situation the resource is involved :
o Master for out of any context definition
o Usage for qualitative involvement of resources in Definition and
Execution of the knowledge meta-model
o Capability for quantitative instances of resources in the capability
model
- Entity is the tangible, identified resource
To this object are associated:
- Properties that characterize the object
- Test specifications associated to properties
- Test results of the time-stamped triplet Entity/Property/Test specification
Fig. . Resource meta-model
The following figure shows an example of a type of resource not defined by ISA95, though very usual in industry: the packing unit that combines a certain quantity of
product and a packaging item. The abstract, recursive meta-model allows a
straightforward definition that still conforms to ISA-95 inner spirit. This
heterogeneous combination of a “container” and a “material” is not possible using the
native ISA-95 model.
Fig. . Example of extending the ISA-95 resource concept
Resource master meta-model mapping
The resource meta-model is specialized in 4 subclasses in the studied standards.
Only ISA-95 handles resources in a detailed manner (not in Part 3 though). Other
standards treat resources superficially.
Metamodel
Resource
Master
>Personnel
Resource
Master
>Role based
equipment
>Physical
asset
>Equipment
entity
Resource
Master
>Material
Resource
Master
>reference
ISA95.02
Personne
l
ISA95.04
Role
based
equipment,
Physical
asset,
physical
model,
ISA88.01/2/4
Equipment
entity,
Physical
model
Material
Formula
ISA88.03
Equipment
requirement
ISATR106.01
Physical
model
Material
definition
Resource
relationship
network
Resource Master > Personnel
Only ISA-95 part 2 defines the Personnel resource. It is represented in the
following UML class diagram.
0..n
0..n
Personnel
Class
Person
< Defined by
0..n
Has
properties
of >
0..n
Is tested
by a >
Has
values for >
Is tested
by a >
0..n
0..n
Qualification
Test
Specification
0..n
Is tested
by a >
0..n
Personnel
Class Property
0..n
Qualification
Test
Result
< Records the
execution of
0..n
Defines a
procedure for
obtaining a >
0..n
0..n
Person
Property
< Maps to
0..n
0..n
< may contain nested
< may contain nested
Fig. . ISA-95 Personnel model
The meta-model mapping is defined in the following table:
Resource
metamodel
Resource type
ISA-95
Personnel
model
“Personnel”
Type property
Resource entity
Person
Entity property
Resource Role
Person property
Personnel class
Role property
Resource category
Category property
Test specification
Test result
Personnel class property
Qualification
test
specification
Qualification test result
Comments
This is the model itself.
ISA-95 does not recognize
explicitly the meta-concept
of resource.
Not explicit in ISA-95
Recursivity
is
not
used/allowed in ISA-95
Recursivity
is
not
used/allowed in ISA-95
Not used
Not used
Resource Master > Equipment
ISA-95 defines 2 similar models to represent equipment.
• the role based equipment model corresponds to the equipment in action in
the facility;
• the physical asset model corresponds to the static asset from its financial or
maintenance viewpoint.
Any actual equipment can be represented in both models within different
hierarchies, providing different attributes that are relevant in context. This association
is handled by a specific data object.
They are represented in the following UML class diagrams.
Fig. . Table . Figure ISA-95 Equipment models
The meta-model mapping is defined in the following table:
Resource metaISA-95
Role
ISA-95
model
based equipment Physical asset
model
model
“Role
based
“Physical
Resource type
equipment”
asset”
Type property
Resource entity
Entity property
Resource Role
Equipment
Equipment
property
Equipment class
Physical asset
Physical asset
property
Physical asset
Comments
This
is
the
model itself. ISA95
does
not
recognize explicitly
the meta-concept of
resource.
Not explicit in
ISA-95
Recursivity
is
class
Role property
Resource
category
Category
property
Test
specification
Test result
N/A
Equipment class
property
-
Physical asset
class property
-
Physical asset
capability
test
specification
Physical asset
capability
test
result
Equipment asset mapping
not used/allowed in
ISA-95
Not used
Not used
Equipment
capability
test
specification
Equipment
capability test result
Can be handled
by the recursivity
that allows mixing
different types of
resources
(the
physical asset can
be embedded in the
role
based
equipment)
Resource Master > Material
The material model is more complete, involving material definition, class as
category, lots and sublots. It is represented in the following UML class diagram.
Fig. . ISA-95 Material model
The meta-model mapping is defined in the following table:
Resource
metamodel
Resource type
ISA-95 Material model
“Material”
Type property
Resource entity
Material lot / sublot
Entity property
Resource Role
Material lot property
Material definition
Role property
Comments
This is the model itself.
ISA-95 does not recognize
explicitly the meta-concept
of resource.
Not explicit in ISA-95
Sublots is useless as the
lot is recursive (kept for
compatibility with old ISA95 versions)
Material
definition
property
Material class
Material class property
Material
test
specification
QA test result
Resource category
Category property
Test specification
Test result
Recursivity
is
not
used/allowed in ISA-95
6. Spatial view - Process
Process meta-model
A Process represents one aspect of knowledge as a structured course of actions to
achieve an objective. The 3 standards address functional knowledge of industrial
facilities with significant overlap.
ISA-95 defines segment, definition, capability, schedule and performance; ISA-88
defines several types of recipe; ISA-106 defines procedure. All these specific
concepts collapse into 3 contextualized concepts, bub-classes:
- Master is used for the definition of processes
- Execution is used for activity programs
- Capability is used for the time projection of means – resources and master
processes
The process itself includes:
- Resource instances – the qualified/quantified, allocable/allocated resources
for its accomplishment
- Parameters – the data inputs for influencing its implementation
- Data – the data outputs to report its execution
Fig. . Process Meta-model
Process meta-model mapping
The 3 process subclasses subclasses are handled by ISA-88 and ISA-95. ISA-106
only defines the Master process subclass.
All standards look at the processes from 2 viewpoints: the product view that
describes the requirements for making the product and the equipment view that
describes the ability of the facility to fulfil these requirements. The meta-model does
not make this distinction.
in the studied standards. Only ISA-95 handles resources in a detailed manner.
Other standards treat resources superficially.
The meta-model mapping is defined in the following table:
Process
Metamodel
ISA95.02
ISA95.04
Process
>master
(ability)
Proces
s segment
Process
>master
Operat
ions
Work
Master
Workfl
ow
specificati
on
Work
definition
I
SA95.0
3
ISA88.01/2/4
ISA88
.03
Equip
ment
Procedur
al
Element
Master
, control
ISATR106.01
Implemen
tation
modules
Equip
ment
Procedure
Requirement
(requireme
nt)
definition
Produc
t segment
Work
directive
Process
>execution
Operat
ions
schedule
Operat
ions
performa
nce
Work
schedule
Operat
ions
capability
Work
capability
Process
>execution
Process
>capability
Work
performan
ce
Recipe
Proces
s model
Gener
al,
site
recipe
Recip
e
Procedur
al
element
Batch
schedule
independ
ent recipe
Proces
s element
s
Procedure
Implementat
ion
Produ
ction
Informati
on
Batch
record
Process >master
This model describes the process and activities as potentially applicable know-how
as a catalog of capabilities, services, products. It applies to two viewpoints:
- The capability as the processing know-how embedded in the facility that can
be applied in different circumstances and products;
- The requirements as the processing know-how specification to make a
product regardless the facility that implements it.
The three standards are explicit on this distinction, though from a different
perspective. ISA-95.02 defines process segment vs operations segments; ISA-88
defines Recipe and Equipment; ISA-106 defines Requirements and Implementation
They induce a difference between the upper level object (i.e. Definition, Recipe,
Procedure…) and its breakdown (Segment, Directive, Procedural element,
Requirement, Module). This may be confusing because they are semantically identical
(a segment can be itself a definition from a more local perspective).
The meta-model demonstrates the possible simplification recognized de facto in
ISA-95 part 4 that equates Work master, Work directive and Work definition as
common, recursive processing descriptions. Actually, an activity in a process is
always itself a process: the recursivity stops to the level of detail addressed by the
model.
ISA-95 Workflow specification ads a structured, machine interpretable description
of the process.
Process >execution
This model describes the work to be done, under execution or executed. It adds
time related planning information to process master. Only ISA-88.01/02 and ISA95.02/4 address this aspect. ISA-95 adds the suffix Schedule or Performance for
planned or realized work though the models are basically identical. ISA-88 part 2 also
defines the schedule notion while ISA-88 part 4 consolidates execution information
into a comprehensive structure that incorporates ISA-95 Operations performance and
numerous resource or process related objects.
Process >capability
Capability is only defined by ISA-95. It is actually a query model for various
criteria: time, localization, availability… Capability applies to resources directly or
through processes.
7. Time view
Functional meta-model
The time view takes the operational context of the industrial facility to define or
observe its behavior.
Unlike spatial view, that characterize the ability or the status of the system at a
given point in time, the time view addresses the functioning, the unfolding of
successive states of the system in time. This links to the execution of processes
addressed in the spatial view, but from their trigger, monitoring, analysis viewpoint.
The time dimensions are not formally addressed in any of these standards. For
example, an operations schedule is part of the spatial view because it is a piece of
knowledge that can be potentially actioned. The time view addresses the building of
this schedule, the triggering of the orders, the monitoring of the subsequent
manufacturing, making the factory actually moving.
The meta-model is a simple structured classification scheme of the standards’
functional concepts. It defines a recursive Function meta-object to describe all useful
level from macro processes to elementary tasks in all operating contexts.
- Functional representation context is supported by the element lifecycle that
guides description detail requirement, from identification of the business
needs to the operations documentation
- Temporal dimension links the function to the decisional hierarchy as
suggested by the ISA standards
Operations Process Management :
This dimension addresses operational business processes such as
demand management, work order monitoring, performance
management. It is decoupled from physico-chemical-biological
transformations and operational knowledge of industrial activities.
o Physical Process Management :
This dimension addresses the management of physical processes
such as product quality and performance criteria, facility capability
and performance. It takes systemically the physical process as a
black box, observing I/Os, sending low variety orders, measuring
operational and economical results.
o Physical Process Control
This dimension addresses the execution of physical processes to
realize the ordered products or services such as routings, recipes,
operating procedures. It is at the heart of the enterprise specific
know-how.
o Equipment control
This dimension addresses information support to equipment to
make them capable of offering the required process services for
executing physical processes, including basic automation and
control. It is at the heart of the engineering knowledge of industrial
facilities.
Granularity corresponds to the different concepts in the functional hierarchy
for every dimension, every standard, such as Procedure, Unit procedure ;
Operation, Phase in ISA-88; Operations definition, Work definition,
Operations segment, Work segment, Activity, Task… in ISA-95
Operation category is introduced by Isa-95 for classifying operational
functions (Production, Maintenance, Quality, Inventory)
o
-
-
Fig. . Function meta-model
Function meta-model mapping
The meta-model mapping is defined in the following table:
Métamodèle
Equipment
control
ISA95.03
Physical
process
control
Physical
process
management
Definition
management
ISA88.01/2/4
Basic
control
Procedural
control
Coordinati
on control
Process
control
ISA88.03
ISATR106.01
Implementati
on modules
Procedure
Implementation
Procedure
Implementation
Unit
supervision
Recipe
management
Procedure
Requirement
Transformati
on of equipment
independent
recipes to master
recipes
Operations
process
management
Resource
Management
Detailed
scheduling
Dispatchi
ng
Execution
management
Tracking
Data
collection
Performa
nce analysis
Production
planning and
scheduling
Process
cell
management
Production
information
management
8. Conclusion
The ISA standards presented in this article are well known and largely
adopted in industry.
We could regret their seemingly lack of consistency and the considerable
volume of this documentation due to the segmented, consensual mode of
development without common guideline by independent committees over a
long period.
It is unlikely that these standards will adopt an ontological design approach as
presented here. They will keep evolving, enriching under the same spirit as
long as they represent an interest for industrialists. Recent updates extended,
clarified, and aligned their definitions. ISA-88 ended up validating heretic
interpretations of its original concepts, ISA-95 added a 4 th part that bring
confusion more that addressing real problems.
This study shows that this huge documentation might collapse into few
abstract concepts, highlighting and encouraging conceptual convergence that
was not envisioned in the context of their development.
These standards have reached a certain maturity and have proved their
value, while applications are still lagging behind their true potential:
- ISA-88 object oriented design, knowledge management based
approach is still not applied. The vision merely goes beyond the
project, with minimal know-how reuse from one application to another,
even less at the enterprise and supra-enterprise levels. Its
generalization beyond batch processes is hindered by its title and the
committee reluctance – they preferred to create a new standard for
continuous processes (ISA-106).
-
-
The supply chain benefits of a certain attention: ISA-95 is often
involved for integrating demand processes. However, the functional
approach and application integration of the design chain respectively
addressed by ISA-88 and ISA-95 are rarely used.
The interest of an industrial information repository begins to be
perceived (traceability, performance and process improvement). The
ISA-88 part 4 is an invaluable resource that is definitely misplaced in
this “batch” tagged standard. It should be moved to ISA-95 instead.
Industrialists will find in these standards conceptual elements and guidelines
for an effective design addressing most of the functional aspects of industrial
IT within all the control chain, from operational planning to equipment control,
from product and facility design to launch in production.
They are not perfect nor comprehensive, but the appropriation of their
underlying concepts revealed by this study shall help to build an enterprise
wide framework within which standards can be adapted and expanded to
cover actual business needs.
Jean Vieille
SyntropicFactory, Control Chain Group, Interaxys
j.vieille@syntropicfactory.com
Abstract. Considered together the ISA-88, 95 and 106 standards can be
intimidating and confusing due to their large, overlapping scope, their different
level of specialization and viewpoint. However their shared history, expert
community, and domain of interest makes them conceptually consistent. This
article proposes three simple but still expressive models to address the intended
use cases of these standards. They can be specialized in any of the models in
these standards providing a robust basis for an object oriented implementation.
They can be used independently of these standards to develop industry /
enterprise specific interoperability and functional design languages.
1. Introduction
The story began in 1990 with the ISA-88 « Batch control » standard that addresses
modular automation for flexible batch processes. It was followed by the ISA-95
« Enterprise – control systems integration » standard that deals with manufacturing
operations management (MOPM, MES) and interoperability. The latest ISA-106
“Procedural Automation for Continuous Process Operations” standard tackles
procedural control for continuous processes. These standards provide good
engineering practices for improving control design for industrial facilities. ISA-88 and
ISA-95 are respectively published as international standards IEC61512 and
ISO/IEC62264.
These standards share genetic concepts due to their consanguinity: many experts
have contributed in the three standardization committees, which originated in ISA88.
Though their viewpoint, terminology and abstraction level sensibly differ, the way
they handle structural and behavioural aspects is relatively consistent, allowing a
quite straightforward retro engineering of their implied meta-model.
The interest of extracting a common meta-model of these standards is two-fold:
- It allows understanding the respective scope of each standard and their
overlap.
- It makes easier to consider interoperability in the broader architectural
approach of enterprise transformation
Despite its technical and specialized content, this article may be of interest even for
people who are not fluent in the discussed standards, but who could appreciate that
the thousand pages of these standards can be summarized into 3 simple generic
models.
This short article does not develop extensively the derivation of the proposed metamodel into specific objects in the quoted standards. However, this meta-model has
been successfully experimented both in the context of leveraging the standards within
a small company that could not afford large consulting rates for implementing a
compliant approach for interoperability and for developing an open, “lean B2MML”
XML schema definition capable of handling any standard objects as well as company
specific concepts.
2. Short overview of the discussed standards
ISA-88: functional design for control
Le ISA-88 standard « Batch Control » defines concepts and terminology for the
design of automation of flexible batch facilities. It features the following aspects:
Modular automation design.
The standard enforces modular design and encourages object design by improving
the potential of reuse of automation objects. This leads to reduced engineering effort,
better knowledge management and more robust and evolvable applications
Industrial system flexibility.
Control is an integrated part of the facility that aims both at driving and at
constraining the number of its possible states. When the number of products or
services the facility has to deliver increases, the number of permitted states increases:
control becomes more involved, hence potentially more difficult to implement.
Flexibility expresses the ability of the facility to handle effectively the required
behavior for each expected outcome under variable internal or external conditions.
Control is for example challenged for delivering different products using different
equipment, or the same product using different equipment which is a root requirement
addressed by ISA-88.
Interoperability and Information.
ISA-88 provides a language (models and terminology, grammar and vocabulary)
that may be used to support interactions between process engineers, operators,
software vendors and system integrators. Data structures help for exchanging
information between applications and for contextualizing it in production databases.
Description and Industrialization of manufacturing processes.
ISA-88 proposes to formalize (1) the product making knowledge in terms of
physico-chemical transformations required to obtain a product with specified
characteristics, (2) the operations sequencing for making the product in a given
facility, and (3) a way to transform the neutral requirements (1) into executable
operating procedures (2)
Applications.
ISA-88 is first a reference for the functional design of automation applications.
Dedicated to flexible batch processes, it applies also to other manufacturing strategies
that are considered less constraining, problematic for control engineers.
ISA-88 keeps distant from technology and does not fundamentally require specific
features of DCS, PLC or SCADA/MES applications. However, It software vendors
propose many ISA-88 labelled solutions: design tools, batch managers, data
historians, and automation objects libraries.
ISA-95: MOM/MES and Interoperability
The ISA-95 standard defines data models for exchanging information between
manufacturing related applications (ERP, MES, SCADA, LIMS, MMS, WMS…) as
well as an activity framework for gathering requirements, designing functions,
urbanizing applications for supporting manufacturing operations.
Industrial system operations management.
The ISA-95 standard discusses extensively the information supports to operations
of industrial systems.
It is the de facto reference for managing the lifecycle of MES (Manufacturing
execution systems) / MOM (Manufacturing Operations Management) domain
functionalities (requirement, design urbanization, operations). It establishes a multidimensional map for managing related documentation and IT assets.
Interoperability.
ISA-95 define data structures for exchanging information between concerned
applications. The UML models are implemented as XML schemas in B2MML.
Applications.
Opposite to ISA-88, ISA-95 seeks neutrality toward manufacturing typology. It is
used as a functional design guide for information support to industrial systems and for
the design standard for interfaces between software applications.
Software vendors have sometime used the data models to design their application
persistence layer.
ISA-106: Procedural Automation for Continuous Process Operations
Launched in 2010, the ISA106 aims at promoting automated procedures in
continuous processes. These processes were mainly designed for mass production, but
are more and more required to be agile and optimized in terms of operations. The
recent emphasis to safety, throughput and quality led to this effort to best design the
automated starting, shutdown and exception handling of these facilities. The first
technical report proposes models and terminology partially inspired from ISA-88 and
ISA-95 to handle procedural design from requirement gathering to implementation.
3. Upper meta-model
The conceptualization of these standards builds on an upper level ontology that
combines elementary concepts within the space-time continuum broken down to
allow our World perception
The spatial view seeks to represent the observed system according to its shapes,
non-time related characteristics. It is static, meaning that the representation from the
observation at a given point in time is complete, or will not improve by a longer
observation, supposing that all relevant information is captured instantaneously. This
view can - will - evolve with time due to the continuous entropic (conflicts, “wear and
tears”, market lagging) and negentropic (engineering, organization) transformation of
the system and to its internal activities, ongoing interactions. However, this view does
not address the “movement”: it is a picture, not a movie.
The temporal view represents the behaviour of the system, its functioning: process
execution, event and subsequent activities that realize the system objectives.
Fig. . Upper meta-model
From a transversal perspective, the system representation builds from a primary
classification of the concepts involved in the existence and activity of the system:
matter, energy and information. This is yet another human way of braking down a
fundamental continuum in order to facilitate observation, understanding.
These abstract concepts are the building blocks for the representations in the spatial
and temporal views. Their meaning in the context of industrial systems as presented in
the ISA-88/95 and 106 standards can be easily reified:
Matter
• The input/outputs of the system as material, parts and products that are
bought, stored, elaborated, transformed, mixed, assembled, wasted, sold
• The components of the system as equipment that are installed, used,
maintained.
Energy
• The input/outputs of the system as energy bought, stored, consumed,
produced, wasted : fluids in closed circuits, electricity, combustibles
• Workforce involved in the system operation
Information
•
•
•
•
Knowledge accrued in the system: product and process know-how
Available documentation, used and created for or by the system operation,
Organisation,
Money available, spend, earned for and by the system operation, financial
aspects.
The meta-model is now complete. The right rectangle is the spatial view (the
system as it is observed in a specific point in time (the potentiality of the system); the
left pyramid is the time view (the kinetics of the system in action).
Fig. . Meta model for the study of ISA-88/95/106 standards
In the spatial view, elementary concepts – simple rectangles are considered under
their potentiality, regardless their involvement in operations.
In the time view, the pyramid represent the decisional / behavioural hierarchy of
the system in operation. The elementary concepts are arrowed: they are involved /
allocated to participated in the system activity (kinetics)
Space-time relationship.
The time and spatial view split is convenient to grasp the complexity of the
industrial system. In reality, they are tightly coupled because the living system keep
evolving with time. Unless the factory is stopped, under nitrogen conservation, the
spatial view is never up-to-date, it is only a representation snapshot if its state at a
specific point in time.
Fig. . Time-space coupling
In practice, the spatial view will describe the operating situations of the system in
action, identifying and describing the Processes that are part of the spatial view as a
knowledge asset, while the time view will consider the actual operation making use of
this knowledge.
4. Application to ISA standards
Applying this upper level meta-model to ISA-88, ISA-95 and ISA-106 consists in
specializing its generic concepts into each of these standards’ equivalent concepts.
This specialization takes into account the application domain and terminology of the
target standards. This is a “reification process” that derives abstract concepts into
more real, tangible ones.
Fig. . Meta-model reification
Elementary dimensions
The notions of matter and energy are not always clearly segregated. An electrical
consumption is with no much doubt considered as « pure energy”, but oil holds
obviously both dimensions. In reality, matter and energy, which are physically so
distinct, are always combined in tangible streams involving the combination of matter
and energy driven by machines and people.
To escape this ambiguity, the meta-model, as ISA-95 will not make a distinction
between both. Actually, from the enterprise viewpoint, matter and energy are of the
same nature: they are both inputs and outputs of their main value chain process, not
something that is part of them as a constituency asset. This does not preclude specific,
different management approaches to energy and matter streams.
ISA-95 defines the notion of Resource that takes matter and energy as one of them
along with people (person) and machines (role based equipment and physical asset)
that is understandable in the context of ISA-88 and ISA-106.
The de-correlated resource description always appears in the context of an activity:
in-formation gives form to something. In this original sense, information is at the
hearth of the transformation processes seeking a useful outcome: combining matter
and energy carelessly, without any knowledge will move the matter to an equal
entropy state at best while an organized, knowledge based process will produce a
more sophisticated process than the original combination of raw material.
This knowledge – information- is potential as long as it says in peoples and
computers memories, kinetics when it is in action. In the latter case, Information
sticks to the action it make productive by consuming energy unless it is useless or
entropic (can it be negative information?). Said another way: during an industrial
process transformation, the entropy of the blend of incorporated material decreases by
consuming energy, countering the so-called fated entropy increase of the universe.
For this reason, the information dimension appears under the more practical, less
open ended term Process applicable (with some possible confusing broadened
definition) to many elements of resources mobilization quoted with numerous terms
in the standards. For example, ISA-95 part 2 Product definition, Product segment,
Process segment, Production request … correspond to Processes in the meta model.
Spatial view
ISA standards focus on operational aspects of industrial systems, not on their
transformation. Resources are summarily addressed in the context of their
contribution to operations. Processes in ISA standards mainly address operational
activities to fulfil short-term market demand. ISA-88 par 3 goes further by tackling
product design to manufacturing. The spatial view is then limited to the description of
basis physical and informational entities involved in manufacturing.
Time view
From the studied standards, the time representation of the operating system can be
represented as a decisional, functional, behavioural hierarchy of four levels:
Operations Process Management for operational processes, Physical Process
Management and Physical Process Control for management and control of physical
equipment.
5. Spatial view - Resource
Resource meta-model
Only ISA-95 proposes a resource model. Other ISA standards address partial
aspects that are all more extensively defined in ISA-95.
ISA-TR106-01 does not offer a formal model; it only defines an alternate
terminology for ISA-88 concepts.
The resource meta-model presented in the following figure includes the following
sub-classes
- Type corresponds to the ISA-95 canonical model such as Equipment,
Material, Person and other specifics
- Role is a functional classification that allows to allocate resource
quantitatively and qualitatively without naming explicitly the corresponding
resources. It corresponds to ISA-95 class concept in equipment and
personnel resource, or material definition in material resource.
- Category is a complementary classification less constraining that roles to
further adapt resource definition to specific businesses. It corresponds to
ISA-95 Class concept in the material model.
- Context defines the situation the resource is involved :
o Master for out of any context definition
o Usage for qualitative involvement of resources in Definition and
Execution of the knowledge meta-model
o Capability for quantitative instances of resources in the capability
model
- Entity is the tangible, identified resource
To this object are associated:
- Properties that characterize the object
- Test specifications associated to properties
- Test results of the time-stamped triplet Entity/Property/Test specification
Fig. . Resource meta-model
The following figure shows an example of a type of resource not defined by ISA95, though very usual in industry: the packing unit that combines a certain quantity of
product and a packaging item. The abstract, recursive meta-model allows a
straightforward definition that still conforms to ISA-95 inner spirit. This
heterogeneous combination of a “container” and a “material” is not possible using the
native ISA-95 model.
Fig. . Example of extending the ISA-95 resource concept
Resource master meta-model mapping
The resource meta-model is specialized in 4 subclasses in the studied standards.
Only ISA-95 handles resources in a detailed manner (not in Part 3 though). Other
standards treat resources superficially.
Metamodel
Resource
Master
>Personnel
Resource
Master
>Role based
equipment
>Physical
asset
>Equipment
entity
Resource
Master
>Material
Resource
Master
>reference
ISA95.02
Personne
l
ISA95.04
Role
based
equipment,
Physical
asset,
physical
model,
ISA88.01/2/4
Equipment
entity,
Physical
model
Material
Formula
ISA88.03
Equipment
requirement
ISATR106.01
Physical
model
Material
definition
Resource
relationship
network
Resource Master > Personnel
Only ISA-95 part 2 defines the Personnel resource. It is represented in the
following UML class diagram.
0..n
0..n
Personnel
Class
Person
< Defined by
0..n
Has
properties
of >
0..n
Is tested
by a >
Has
values for >
Is tested
by a >
0..n
0..n
Qualification
Test
Specification
0..n
Is tested
by a >
0..n
Personnel
Class Property
0..n
Qualification
Test
Result
< Records the
execution of
0..n
Defines a
procedure for
obtaining a >
0..n
0..n
Person
Property
< Maps to
0..n
0..n
< may contain nested
< may contain nested
Fig. . ISA-95 Personnel model
The meta-model mapping is defined in the following table:
Resource
metamodel
Resource type
ISA-95
Personnel
model
“Personnel”
Type property
Resource entity
Person
Entity property
Resource Role
Person property
Personnel class
Role property
Resource category
Category property
Test specification
Test result
Personnel class property
Qualification
test
specification
Qualification test result
Comments
This is the model itself.
ISA-95 does not recognize
explicitly the meta-concept
of resource.
Not explicit in ISA-95
Recursivity
is
not
used/allowed in ISA-95
Recursivity
is
not
used/allowed in ISA-95
Not used
Not used
Resource Master > Equipment
ISA-95 defines 2 similar models to represent equipment.
• the role based equipment model corresponds to the equipment in action in
the facility;
• the physical asset model corresponds to the static asset from its financial or
maintenance viewpoint.
Any actual equipment can be represented in both models within different
hierarchies, providing different attributes that are relevant in context. This association
is handled by a specific data object.
They are represented in the following UML class diagrams.
Fig. . Table . Figure ISA-95 Equipment models
The meta-model mapping is defined in the following table:
Resource metaISA-95
Role
ISA-95
model
based equipment Physical asset
model
model
“Role
based
“Physical
Resource type
equipment”
asset”
Type property
Resource entity
Entity property
Resource Role
Equipment
Equipment
property
Equipment class
Physical asset
Physical asset
property
Physical asset
Comments
This
is
the
model itself. ISA95
does
not
recognize explicitly
the meta-concept of
resource.
Not explicit in
ISA-95
Recursivity
is
class
Role property
Resource
category
Category
property
Test
specification
Test result
N/A
Equipment class
property
-
Physical asset
class property
-
Physical asset
capability
test
specification
Physical asset
capability
test
result
Equipment asset mapping
not used/allowed in
ISA-95
Not used
Not used
Equipment
capability
test
specification
Equipment
capability test result
Can be handled
by the recursivity
that allows mixing
different types of
resources
(the
physical asset can
be embedded in the
role
based
equipment)
Resource Master > Material
The material model is more complete, involving material definition, class as
category, lots and sublots. It is represented in the following UML class diagram.
Fig. . ISA-95 Material model
The meta-model mapping is defined in the following table:
Resource
metamodel
Resource type
ISA-95 Material model
“Material”
Type property
Resource entity
Material lot / sublot
Entity property
Resource Role
Material lot property
Material definition
Role property
Comments
This is the model itself.
ISA-95 does not recognize
explicitly the meta-concept
of resource.
Not explicit in ISA-95
Sublots is useless as the
lot is recursive (kept for
compatibility with old ISA95 versions)
Material
definition
property
Material class
Material class property
Material
test
specification
QA test result
Resource category
Category property
Test specification
Test result
Recursivity
is
not
used/allowed in ISA-95
6. Spatial view - Process
Process meta-model
A Process represents one aspect of knowledge as a structured course of actions to
achieve an objective. The 3 standards address functional knowledge of industrial
facilities with significant overlap.
ISA-95 defines segment, definition, capability, schedule and performance; ISA-88
defines several types of recipe; ISA-106 defines procedure. All these specific
concepts collapse into 3 contextualized concepts, bub-classes:
- Master is used for the definition of processes
- Execution is used for activity programs
- Capability is used for the time projection of means – resources and master
processes
The process itself includes:
- Resource instances – the qualified/quantified, allocable/allocated resources
for its accomplishment
- Parameters – the data inputs for influencing its implementation
- Data – the data outputs to report its execution
Fig. . Process Meta-model
Process meta-model mapping
The 3 process subclasses subclasses are handled by ISA-88 and ISA-95. ISA-106
only defines the Master process subclass.
All standards look at the processes from 2 viewpoints: the product view that
describes the requirements for making the product and the equipment view that
describes the ability of the facility to fulfil these requirements. The meta-model does
not make this distinction.
in the studied standards. Only ISA-95 handles resources in a detailed manner.
Other standards treat resources superficially.
The meta-model mapping is defined in the following table:
Process
Metamodel
ISA95.02
ISA95.04
Process
>master
(ability)
Proces
s segment
Process
>master
Operat
ions
Work
Master
Workfl
ow
specificati
on
Work
definition
I
SA95.0
3
ISA88.01/2/4
ISA88
.03
Equip
ment
Procedur
al
Element
Master
, control
ISATR106.01
Implemen
tation
modules
Equip
ment
Procedure
Requirement
(requireme
nt)
definition
Produc
t segment
Work
directive
Process
>execution
Operat
ions
schedule
Operat
ions
performa
nce
Work
schedule
Operat
ions
capability
Work
capability
Process
>execution
Process
>capability
Work
performan
ce
Recipe
Proces
s model
Gener
al,
site
recipe
Recip
e
Procedur
al
element
Batch
schedule
independ
ent recipe
Proces
s element
s
Procedure
Implementat
ion
Produ
ction
Informati
on
Batch
record
Process >master
This model describes the process and activities as potentially applicable know-how
as a catalog of capabilities, services, products. It applies to two viewpoints:
- The capability as the processing know-how embedded in the facility that can
be applied in different circumstances and products;
- The requirements as the processing know-how specification to make a
product regardless the facility that implements it.
The three standards are explicit on this distinction, though from a different
perspective. ISA-95.02 defines process segment vs operations segments; ISA-88
defines Recipe and Equipment; ISA-106 defines Requirements and Implementation
They induce a difference between the upper level object (i.e. Definition, Recipe,
Procedure…) and its breakdown (Segment, Directive, Procedural element,
Requirement, Module). This may be confusing because they are semantically identical
(a segment can be itself a definition from a more local perspective).
The meta-model demonstrates the possible simplification recognized de facto in
ISA-95 part 4 that equates Work master, Work directive and Work definition as
common, recursive processing descriptions. Actually, an activity in a process is
always itself a process: the recursivity stops to the level of detail addressed by the
model.
ISA-95 Workflow specification ads a structured, machine interpretable description
of the process.
Process >execution
This model describes the work to be done, under execution or executed. It adds
time related planning information to process master. Only ISA-88.01/02 and ISA95.02/4 address this aspect. ISA-95 adds the suffix Schedule or Performance for
planned or realized work though the models are basically identical. ISA-88 part 2 also
defines the schedule notion while ISA-88 part 4 consolidates execution information
into a comprehensive structure that incorporates ISA-95 Operations performance and
numerous resource or process related objects.
Process >capability
Capability is only defined by ISA-95. It is actually a query model for various
criteria: time, localization, availability… Capability applies to resources directly or
through processes.
7. Time view
Functional meta-model
The time view takes the operational context of the industrial facility to define or
observe its behavior.
Unlike spatial view, that characterize the ability or the status of the system at a
given point in time, the time view addresses the functioning, the unfolding of
successive states of the system in time. This links to the execution of processes
addressed in the spatial view, but from their trigger, monitoring, analysis viewpoint.
The time dimensions are not formally addressed in any of these standards. For
example, an operations schedule is part of the spatial view because it is a piece of
knowledge that can be potentially actioned. The time view addresses the building of
this schedule, the triggering of the orders, the monitoring of the subsequent
manufacturing, making the factory actually moving.
The meta-model is a simple structured classification scheme of the standards’
functional concepts. It defines a recursive Function meta-object to describe all useful
level from macro processes to elementary tasks in all operating contexts.
- Functional representation context is supported by the element lifecycle that
guides description detail requirement, from identification of the business
needs to the operations documentation
- Temporal dimension links the function to the decisional hierarchy as
suggested by the ISA standards
Operations Process Management :
This dimension addresses operational business processes such as
demand management, work order monitoring, performance
management. It is decoupled from physico-chemical-biological
transformations and operational knowledge of industrial activities.
o Physical Process Management :
This dimension addresses the management of physical processes
such as product quality and performance criteria, facility capability
and performance. It takes systemically the physical process as a
black box, observing I/Os, sending low variety orders, measuring
operational and economical results.
o Physical Process Control
This dimension addresses the execution of physical processes to
realize the ordered products or services such as routings, recipes,
operating procedures. It is at the heart of the enterprise specific
know-how.
o Equipment control
This dimension addresses information support to equipment to
make them capable of offering the required process services for
executing physical processes, including basic automation and
control. It is at the heart of the engineering knowledge of industrial
facilities.
Granularity corresponds to the different concepts in the functional hierarchy
for every dimension, every standard, such as Procedure, Unit procedure ;
Operation, Phase in ISA-88; Operations definition, Work definition,
Operations segment, Work segment, Activity, Task… in ISA-95
Operation category is introduced by Isa-95 for classifying operational
functions (Production, Maintenance, Quality, Inventory)
o
-
-
Fig. . Function meta-model
Function meta-model mapping
The meta-model mapping is defined in the following table:
Métamodèle
Equipment
control
ISA95.03
Physical
process
control
Physical
process
management
Definition
management
ISA88.01/2/4
Basic
control
Procedural
control
Coordinati
on control
Process
control
ISA88.03
ISATR106.01
Implementati
on modules
Procedure
Implementation
Procedure
Implementation
Unit
supervision
Recipe
management
Procedure
Requirement
Transformati
on of equipment
independent
recipes to master
recipes
Operations
process
management
Resource
Management
Detailed
scheduling
Dispatchi
ng
Execution
management
Tracking
Data
collection
Performa
nce analysis
Production
planning and
scheduling
Process
cell
management
Production
information
management
8. Conclusion
The ISA standards presented in this article are well known and largely
adopted in industry.
We could regret their seemingly lack of consistency and the considerable
volume of this documentation due to the segmented, consensual mode of
development without common guideline by independent committees over a
long period.
It is unlikely that these standards will adopt an ontological design approach as
presented here. They will keep evolving, enriching under the same spirit as
long as they represent an interest for industrialists. Recent updates extended,
clarified, and aligned their definitions. ISA-88 ended up validating heretic
interpretations of its original concepts, ISA-95 added a 4 th part that bring
confusion more that addressing real problems.
This study shows that this huge documentation might collapse into few
abstract concepts, highlighting and encouraging conceptual convergence that
was not envisioned in the context of their development.
These standards have reached a certain maturity and have proved their
value, while applications are still lagging behind their true potential:
- ISA-88 object oriented design, knowledge management based
approach is still not applied. The vision merely goes beyond the
project, with minimal know-how reuse from one application to another,
even less at the enterprise and supra-enterprise levels. Its
generalization beyond batch processes is hindered by its title and the
committee reluctance – they preferred to create a new standard for
continuous processes (ISA-106).
-
-
The supply chain benefits of a certain attention: ISA-95 is often
involved for integrating demand processes. However, the functional
approach and application integration of the design chain respectively
addressed by ISA-88 and ISA-95 are rarely used.
The interest of an industrial information repository begins to be
perceived (traceability, performance and process improvement). The
ISA-88 part 4 is an invaluable resource that is definitely misplaced in
this “batch” tagged standard. It should be moved to ISA-95 instead.
Industrialists will find in these standards conceptual elements and guidelines
for an effective design addressing most of the functional aspects of industrial
IT within all the control chain, from operational planning to equipment control,
from product and facility design to launch in production.
They are not perfect nor comprehensive, but the appropriation of their
underlying concepts revealed by this study shall help to build an enterprise
wide framework within which standards can be adapted and expanded to
cover actual business needs.
Johann Sebastian Bach. the music closest to silence, closest, in spite of its being so highly organized, to pure, one-hundred-degree proof Spirit" (Aldous Huxley, Island)