Operation

An operation represents an activity: these consume and produce material, take time and also require capacity.

An operation consumes and produces material, modeled through flows.

An operation requires capacity, modeled through loads.

Different operation types exist:

  • Models an operation with a duration that is independent of the quantity. A good example is a transport or a procurement operation.
  • Models an operation where the duration increases linear with the quantity. A good example is a manufacturing operation where the duration is determined by the production rate of a machine.
  • Models a choice between different operations.
  • Operation_split (new in 2.2):
    This operation type plans the demand proportionally over a number of sub-operations, using some pre-defined percentages.
  • Models a sequence a number of ‘step’ sub-operations, to be executed sequentially.

Fields

Field Type Description
name non-empty string
Name of the operation.
This is the key field and a required attribute.
description string Free format description.
category string Free format category.
subcategory string Free format subcategory.
location location
Location of the operation.
Default is null.
The working hours and holidays for the operation are taken from the ‘available’ calendar of the location.
fence duration
Time window from the current date of the plan during which all operationplans are expected to be frozen/released.
When the “FENCE” constraint is enabled in the solver, it won’t create any new operation plans in this time fence. Only the externally supplied and locked operationplans will then exist in this time window.
size_minimum positive double
A minimum quantity for operationplans.
The default value is 1.
A request for a lower, non-zero quantity will be rounded up.
size_minimum_calendar calendar
A calendar to define the minimum size of operationplans when this value varies over time. The end date of the operationplan determines which date we use as lookup in the calendar.
If this field is used, the size_minimum field is ignored.
size_multiple positive double A lotsize quantity for operationplans.
size_maximum positive double
The maximum quantity for operationplans.
Note that this value limits the size of individual operationplans. The solver can create multiple operationplans of this maximum size, so this value does NOT constrain the total planned quantity on the operation. The field is useful to break big operationplans in smaller ones.
cost double
The cost of executing this operation, per unit of the operation_plan.
Depending on what the operation models, this represents transportation costs, manufacturing costs, procurement costs, delivery costs, etc...
The raw material cost and the resource usage cost are added to this cost and should not be included in this value.
The default value is 0.
posttime duration
A post-operation time, used as a buffer for uncertain capacity or operation duration.
The solver will try to respect this time as a soft constraint. Ie when required to meet demand on time the post-operation time can be violated.
Resources are not loaded during the post-operation time.
This field is used to model time-based safety stock targets, aka days of inventory. It is then set for the producing operation of a certain buffer.
If you want to model a safety stock quantity, you can use the minimum or minimum_calendar fields on the buffer.
detectproblems boolean
Set this field to false to skip problem detection on this operation.
The default value is true.
loads list of load A list of all resources loaded by this operation.
flows list of flow A list of all buffers where material is consumed from or produced into.
level integer
Indication of how upstream/downstream this entity is situated in the supply chain.
Lower numbers indicate the entity is close to the end item, while a high number will be shown for components nested deep in a bill of material.
The field is export-only.
cluster integer
The network of entities can be partitioned in completely independent parts. This field gives the index for the partition this entity belongs to.
The field is export-only.
hidden boolean Marks entities that are considered hidden and are normally not shown to the end user.
action A/C/AC/R
Type of action to be executed:
A: Add an new entity, and report an error if the entity already exists.
C: Change an existing entity, and report an error if the entity doesn’t exist yet.
AC: Change an entity or create a new one if it doesn’t exist yet. This is the default.
R: Remove an entity, and report an error if the entity doesn’t exist.

Operation_fixed_time

Models an operation with a fixed duration regardless of the quantity. E.g. a transport operation.

This is the default operation type.

Field Type Description
duration duration
Duration of the operation.
The default value is 0.

Operation_time_per

Models an operation where the duration changes linear with the quantity. E.g. a production operation.

The total duration of the operation plan is the sum of:

  • A fixed DURATION.
  • A variable duration, computed as the operationplan quantity multiplied by a DURATION_PER.
Field Type Description
duration duration
Fixed component of the duration of the operationplan.
The default value is 0.
duration_per duration
Variable component of the duration of the operationplan.
The default value is 0.

Operation_alternate

Models a choice between different operations. It has a list of alternate sub-operations listed, each with a priority.

Operation minimum, multiple and maximum size constraints of each individual alternate sub-operation are respected. The ones on the operation_alternate operation itself are ignored.

Field Type Description
search string

Defines the order of preference among the alternate loads.

The valid choices are:

  • PRIORITY
    Select the alternate with the lowest priority number.
    This is the default.
  • MINCOST
    Select the alternate which gives the lowest cost.
    The cost includes the cost of all upstream operations, resources and buffers.
  • MINPENALTY
    Select the alternate which gives the lowest penalty.
    The penalty includes the penalty of all penalties incurred in the upstream plan.
  • MINCOSTPENALTY
    Select the alternate which gives the lowest sum of the cost and penalty.
    The sum is computed for the complete upstream path.
suboperations List of suboperation List of alternate sub-operations.

Suboperation fields:

Field Type Description
operation operation Sub-operation.
owner operation Parent operation
priority integer
For alternate operations: Priority of this alternate.
For routing operations: Sequence number of the step.
For split operations: Proportion of the demand planned along this suboperation.
Lower numbers indicate higher priority.
When the priority is equal to 0, this alternate is considered unavailable and it can’t be used for planning.
Default value is 1.
effective_start dateTime Earliest allowed start date for using this suboperation.
effective_end dateTime Latest allowed end date for using this suboperation.

Operation_split

This operation type plans the demand proportionally over a number of operations. It has a list of alternate sub-operations listed, each with a percentage.

The percentages are treated as a hard constraint by the solver. This means that if one of the alternates can’t deliver the requested quantity, the complete split operation is considered as infeasible. (If we’ld treat it as a soft constraint, we would distribute the infeasible quantity among the other alternates).

Minimum, multiple and maximum size constraints on the sub-operations are respected. This means that we can end up with a split that deviates to some extent from the specified percentages.

The percentages don’t need to add up to 100%. We use the relative ratio’s of the sub-operations.

Field Type Description
suboperations List of suboperation
List of sub-operations to divide the plan across.
See above for the definition of the suboperation.

Operation_routing

Models a sequence a number of ‘step’ sub-operations, to be executed sequentially.

Field Type Description
suboperations List of suboperation
List of sub-operations to execute in sequence.
See above for the definition of the suboperation.

Example XML structures

Adding or changing operations

<plan>
  <operations>
    <operation name="buy item X from supplier" xsi:type="operation_fixed_time">
      <duration>P1D</duration>
    </operation>
    <operation name="make item X" xsi:type="operation_time_per">
      <duration>PT1H</duration>
      <duration_per>PT5M</duration_per>
    </operation>
    <operation name="make or buy item X" xsi:type="operation_alternate">
      <suboperations>
        <suboperation>
          <operation name="make item X" />
          <priority>1</priority>
        </suboperation>
        <suboperation>
          <operation name="buy item X from supplier" />
          <priority>2</priority>
        </suboperation>
      </suboperations>
    </operation>
    <operation name="make subassembly" xsi:type="operation_routing">
      <suboperations>
        <suboperation>
          <operation name="make subassembly step 1" duration="PT1H"/>
          <priority>1</priority>
        </suboperation>
        <suboperation>
          <operation name="make subassembly step 2" duration="PT5M"/>
          <priority>2</priority>
        </suboperation>
      </suboperations>
    </operation>
  </operations>
</plan>

Deleting an operation

<plan>
   <operations>
      <operation name="make item X" action="R"/>
   </operations>
</plan>

Example Python code

Adding or changing operations

op1 = frepple.operation_fixed_time(name="buy item X from supplier", duration=24*3600)
op2 = frepple.operation_time_per(name="make item X", duration=3600, duration_per=60*5)
op3 = frepple.operation_alternate(name="make or buy item X")
frepple.suboperation(owner=op3, operation=op1, priority=1)
frepple.suboperation(owner=op3, operation=op2, priority=2, effective_end=datetime.datetime(2009,10,10))
op4 = frepple.operation_routing(name="make subassembly")
frepple.suboperation(
  owner=op3,
  operation=frepple.operation_fixed_time(name="make subassembly step 1", duration=3600),
  priority=1
  )
frepple.suboperation(
  owner=op3,
  operation=frepple.operation_fixed_time(name="make subassembly step 2", duration=300),
  priority=2
  )

Deleting an operation

frepple.operation(name="make item X", action="R")

Iterate over operations, loads and flows

for o in frepple.operations():
  print("Operation:", o.name, o.description, o.category)
  for l in o.loads:
    print("  Load:", l.resource.name, l.quantity, l.effective_start, l.effective_end)
  for l in o.flows:
    print("  Flow:", l.buffer.name, l.quantity, l.effective_start, l.effective_end)