Work masters

A work master defines the resources and instructions necessary to do a unit of work. As the most granular work definition in ISA-95, the work master can serve a variety of operational purposes:

• Define how to create a product from the perspective of a level-3 system
• Provide a reference document that can be cloned and overridden for detailed scheduling and dispatching
• Store recipes and parameters to be downloaded by the PLC
• Contain parameters to derive metrics for KPI calculations

In the manufacturing ontology, the work master has relationships to resources, other work definitions, and planning entities. Like other work definitions, a work master can be either a pattern, defining a template for work, or an instance, defining a unit of actual work.

Work master attributes

classDiagram
class workMaster{
id: make.PBJ1000
description: Make Packaged Blue Juice
workType: production
duration: 45 minutes
}
    

Along with relationships described in the following sections, work masters have attributes to identify and qualify the type of work being defined. Important attributes include:

ID

A unique ID

Work type

The category of work―one of production, maintenance, quality, or inventory

Duration

The expected time needed to perform the work

Contains resources and parameter specifications

A work master may have specifications that link the work master to its required resources and instructions. In ISA-95 relations, the specification is an intermediary between the work master and the resource or parameter. The work master contains the specifications; the specifications describe the necessary quantities and uses of the resource object that it corresponds to.

classDiagram
class materialSpecification{
  what and how much?
  
}
class personnelSpecification{
  who and how many?
}
class equipmentSpecification{
how?
}

class parameterSpecification{
instructions, checklists,
and so on
}

workMaster *--> materialSpecification :contains
workMaster *--> personnelSpecification :contains
workMaster *--> equipmentSpecification :contains
workMaster *--> parameterSpecification :contains

Example: material specifications

Resource specifications may have attributes that describe information about the use, quantity, and location of the resource. Some specifications, such as material, have additional attributes.

For example, to produce one pallet of Cosmic Blue Juice, The Juice Factory requires 5 cases of Blue Juice and one pallet. The work master to produce this final product specifies three different materials, all of which are used in a different way:

• Consume 5 units of the blue juice case, a material definition
• Produce 1 unit of packed blue juice, a material definition
• Use one pallet, a consumable (material that has no material lot)

classDiagram
class `Work master: Make Cosmic Blue Juice`{
description: procedure to produce pallet of Cosmic Blue Juice
}

class `Specification: blue juice case`{
use: consumed
quantity: 5
quantity_unit_of_measure: juice_case
}
class `Specification: blue juice pallet`{
use: produced
quantity: 1
quantity_unit_of_measure: pallet
}

class `Specification: pallet`{
use: consumable
quantity: 1
quantity_unit_of_measure: pallet
}
class `Material definition: PBJ`{
description: One pallet of cosmic blue juice
}

`Work master: Make Cosmic Blue Juice` *--> `Specification: blue juice case`
`Work master: Make Cosmic Blue Juice` *--> `Specification: blue juice pallet`
`Work master: Make Cosmic Blue Juice` *--> `Specification: pallet`
`Specification: blue juice case` --> `Material definition: PBJ`
`Specification: blue juice pallet` -->  `Material definition: blue juice case`

Parameter specifications

Parameter specifications detail information that is specific to a work master but not specific to any particular resource. For example, the production of bulk juice might have a parameter specification called pre-mix checklist that details a set of steps that the operator must perform before starting the equipment.

Relationships to planning models

As work masters contain resource requirements and instructions, they also provide a source document for detailed scheduling and dispatching. Conventionally, work masters are related to job orders through a work directive entity:

• The job order says what to make
• The work master provides a canonical definition of how to make it
• The work directive provides a version of the work master, recording how work was performed at the time of execution

classDiagram
class jobOrder{
make bulk blue juice
}

class workMaster{
id: WM.Bulk_Blue_Juice
}
class workDirective{
id: WD.Bulk_blue_juice
}

jobOrder --> workDirective :corresponds to
workDirective --> workMaster :derived from 

Corresponds to work directive

A work directive is a clone of the work master that is made at the time of dispatching. If the actual work performed needs to deviate from the work defined in the work master, the work directive provides a way to record the changes in a new definition.

For example, the work master to make bulk blue juice might specify sugar from a specific provider. At the time of production, however, the plant might have only sugar from a different supplier. In this case, the work directive would override the material specification to reflect the substitute material definition. that

Relationships to other work masters

A work master might have relationships to other work masters:

• A work master may contain children work master.
• An instance work master may be defined by a pattern work master.

Parent child-work masters

You can group sub-processes of a work master using a parent-child relationship. For example, the work master to make packed blue juice might have child work masters to bottle, case, and palletize the individual material sublots.

classDiagram
class `WM: bottle`{
equipment_specifcation: bottler
equipment_specifcation: capper
}
class `WM: pack in case`{
equipment_specifcation: casepacker
}
class `WM: palletize`{
equipment_specifcation: palletizer
}

`WM:make blue juice bottle` *--> `WM: bottle` :contains
`WM:make blue juice bottle` *--> `WM: pack in case` :contains
`WM:make blue juice bottle` *--> `WM: palletize` :contains

Defined by patterns

A pattern work master provides a template to build instance work masters for similar production processes.

For example, to produce bulk juice for all five of its juice lines, The Juice Factory requires exactly the same equipment and quantity of sugar. The only item that changes is the material definition for the kits that are dumped into the mixer.

To minimize configuration, The Juice Factory might use a pattern work master that specifies the equipment, sugar, and kit class. Then each brand of juice may have an instance work master that overrides the kits class with its specific kit definition.

classDiagram
class patternWorkMaster{
description: make bulk juice
equipment specifications:
  - mixers
material specifications:
  - 200LB sugar
  - 1 kit from kits class
}

class instanceWorkMaster_blue{
- make bulk blue juice
- requires 1 blue kit
}

class instanceWorkMaster_red{
- make bulk red juice
- requires 1 red kit
}

patternWorkMaster --> instanceWorkMaster_blue :defines
patternWorkMaster --> instanceWorkMaster_red :defines

Corresponds to a process segment

Work masters correspond to process segments, which are less granular, business-level definitions of work. For example, the make juice process segment might have five corresponding work masters that describe how to produce each line of juice at the level of detail necessary for a manufacturing execution system.

classDiagram
namespace process_segment_kitting{
class `WM: make blue juice kit`
class `WM: make red juice kit`
class `WM: make green juice kit`

}

Workflow specifications

The work master may be linked to other work masters in a sequence through a workflow specification. The workflow specification provides an overview of the steps to execute masters in sequence.

Each master can have a node that exists in the workflow specification. For example, here are the production steps to make blue juice. Each node in this workflow might correspond to a work master, with the pack node being a that corresponds to the pack parent work master.