Any project, whether it's cooking a meal or building a house, can be broken down into a set of separate activities.
Some activities cannot be started before others have been finished. For example, when building a house you cannot put in the windows before you have built the walls.
Making a cup of tea involves the following activities:
|A||Boil the kettle|
|B||Put a tea bag in a mug|
|C||Brew the tea|
But there are constraints as some activities depend on each other:
A precedence table helps you organise the activities and shows where there are constraints caused by dependencies. A dependency is where carrying an activity depends on another activity having been carried out.
Notice that a dependency only refers to the activity immediately before the activity in question.
From this table you can see that either A or B could be started first as they do not depend on any other activity.