====== Linking activities ======

In a schedule, activities are usually connected to define their **execution order**.

A link creates a **logical relationship** between two activities called:

  * **predecessor**: activity that must occur before
  * **successor**: activity that depends on the previous one

These relationships allow the schedule to **update automatically** when an activity is modified.

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===== Creating a link between two activities =====

{{:en:gantt:2026-03-12_10h36_11.png?600|}}

To link two activities in the **Gantt chart**:

  - Select the two activities in the desired order while holding the **CTRL** key and **right-click**
  - Select **Create link**
  - Choose **Link two activities**

A link editing window will then open.

In this window, you can define:

  * the **predecessor** activity
  * the **successor** activity
  * the **link type**
  * a possible **lag**

Once the parameters are defined, confirm with **OK** to create the link.

{{:fr:gantt:2026-03-10_10h28_50.png?350|}}

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===== Types of links =====

Several types of relationships can be defined between two activities.

The most common types are:

  * **FS – Finish to Start**  
    the successor activity starts when the previous activity finishes.

  * **SS – Start to Start**  
    both activities can start simultaneously or with a delay.

  * **FF – Finish to Finish**  
    both activities must finish at the same time.

  * **SF – Start to Finish**  
    the successor activity must finish when the previous activity starts.

The **Finish to Start (FS)** type is the most commonly used in project schedules.

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===== Adding a lag =====

It is possible to add a **lag** between two linked activities.

This lag can be expressed in:

  * **elapsed days**
  * or **working units**

A lag can represent for example:

  * drying time
  * a logistics delay
  * a waiting time between two operations

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===== Linking multiple activities =====

The **Create link** menu also allows faster creation of relationships
in certain situations:

  * **Link a sequence**: automatically creates links between several selected activities following the schedule order.

  * **Link multiple activities**: allows several relationships to be created in a single operation.

These tools help quickly structure the scheduling logic.

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===== Editing a link =====

An existing link can be modified at any time.

To do this:

  - Select the activity in the Gantt chart
  - Right-click and choose **Edit**
  - Access the different links in the **Links** tab of the editing window

{{:en:gantt:2026-03-12_10h39_44.png?400|}}

You can then adjust:

  * the relationship type
  * the lag
  * the predecessor or successor activity

From this tab, it is also possible to add links from the **Predecessor**
or **Successor** tables:

{{:en:gantt:2026-03-12_10h39_48.png?400|}}

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===== Spatio-temporal specific features =====

In some projects, additional constraints can be defined
between activities.

These constraints may include:

  * a **minimum geographical distance**
  * a **minimum time separation**

These parameters are particularly useful in **linear projects**
where several teams operate along the same alignment.

They help ensure a **safe distance** or
a **minimum time separation** between two operations.

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===== Role of links in the schedule =====

Links form the **calculation logic of the schedule**.

Once activities are connected, the software can:

  * automatically recalculate dates
  * analyse task dependencies
  * identify the impact of delays
  * ensure the consistency of the schedule

A properly linked schedule therefore becomes a true
**project management and control tool**.