Service Modules > Scheduling and Optimization > Schedule Optimization > Schedule Optimization For Implementers > Working with Dependency Scheduling > Time Dependencies
Time Dependencies
Time dependency is applicable for scenarios with two or more work orders depending on each other based on a time factor. You might have created multiple work orders for a single job, which needs the work orders to be completed in a chronological sequence. In such a scenario, creating a dependency group based on time dependency helps ensure that the work orders are correctly scheduled.
Consider the following examples:
• Two servers in a data center need to shut down simultaneously. To achieve the task:
a. Create two work orders.
b. Create a dependency group with time dependency, specifying that both the work orders should start simultaneously.
• A cooling system needs to be installed and configured. Configuration of the cooling system cannot start till the installation is complete. To achieve the task:
a. Create two work orders for installation and configuration.
b. Create a dependency group with time dependency, specifying that the work order for installation must finish before the work order for configuration starts.​
The following types of time dependencies are supported.
Type of Dependency
Correlation
Description
Example
Natural dependency
Finish > Start
If there are two work orders - WO A and WO B, the following dependencies are applied to achieve the Finish > Start correlation:
• WO A must be completed before WO B can begin.
• WO B cannot start until WO A is completed.
The work order for digging the foundation must be completed before the work order for pouring the concrete can begin.
Sequential dependencies
Start > Start
If there are two work orders - WO A and WO B, the following dependencies are applied to achieve the Start > Start correlation:
• WO B cannot start until WO A starts.
• WO B cannot start before WO A starts.
• WO B can start anytime after WO A has started.
To save time, you want to level concrete at one end of the foundation while it is still being poured at the other end. However, the level concrete task (WO B) cannot start until the pour concrete task (WO A) has also started.
Finish > Finish
If there are two work orders - WO A and WO B, the following dependencies are applied to achieve the Finish > Finish correlation:
• WO A must be completed before WO B can be completed.
• WO B cannot be completed before WO A is completed.
• WO A and WO B do not have to be completed at the same time. WO B can be completed any time after WO A ends.
The team is adding the wiring to the building and inspecting it simultaneously.
The inspection task (WO A) cannot be completed until the wiring task (WO B) is complete.
Start > Finish
If there are two work orders - WO A and WO B, the following dependencies are applied to achieve the Start > Finish correlation:
• WO A must start before WO B finishes.
• WO B cannot be completed before WO A starts.
• WO B can be completed any time after WO A starts.
The roof trusses for the building are built off-site. The team cannot finish the roof assembly task (WO B) until the truss delivery task (WO A) starts.
Unison Dependencies
Start Unison
If there are two work orders - WO A and WO B, the following dependencies are applied to achieve the Start Unison correlation:
• WO B must start at the same time as WO A has started.
• You can set a deviation buffer. For example, WO B can start with a delay of five minutes after WO A starts.
Two servers at a data center must start at the same time.
Finish Unison
If there are two work orders - WO A and WO B, the following dependencies are applied to achieve the Finish Unison correlation:
• WO B must be completed at the same time WO A is completed.
• You can set a deviation buffer. For example, WO B can be completed with a delay of five minutes after WO A is completed.
All the production machines at a factory must switch off simultaneously.
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