If a task is relatively large and requires several users with different skills to manage, break the task into subtasks and create parent-child relationships. A child task is a relatively smaller, manageable size of work.

When you group child tasks together under a parent, values such as Estimated cost aggregate and roll up to the parent task. So the parent task takes on the form of a summary task or rollup task for its child tasks. Planned start date and Planned end date rollup occurs when you create child tasks: the duration of the parent automatically adjusts to cover its child tasks.

A parent-child relationship is different from a dependency relationship. In a dependency, one task must finish before another begins. In a parent-child relationship, any number of tasks can be nested under a parent task with or without any dependencies. When you create a parent-child relationship, the parent task number is saved in the Parent field in the Project Tasks table. All project management tasks have a parent: either another project task or the project itself.

Unlike a dependency, a parent-child relationship is not saved as a record in any table. The only modification that takes place when a parent-child relationship is modified is the Parent field in the child task record.

You can create predecessor-successor relationships between child tasks with different parents, between two different parent tasks, or between a child task and another parent task. However, if the predecessor task finishes after the successor task starts, creating a dependency between child tasks that have different parents is not allowed.