Activities

Defines activities in the data model.
An activity is a task to be completed. Activities are hierarchical in nature. This means that a main activity, called parent activity, can be broken down into subactivities. A subactivity, or child activity, can in turn be a parent activity of other subactivities or, if it is at the very end of a branch of the hierarchy, it is a leaf activity. A leaf activity is an activity that has no child activity.
In addition to its name and identifier, an activity is defined by its start time and end time, which determine an interval called the duration of the activity. If the start and end times are identical, the duration is equal to 0. A zero-duration activity is commonly called a milestone. Typically, milestones are not rendered by the same renderer as activities with a non-zero duration.

Resources

A resource is a means by which an activity can be completed. Resources can be persons, premises, equipment, and so forth. Like activities, resources are also hierarchical in nature.
If resources are people, the parent resource is a department while the child resources are the individual employees. Likewise, you may want to group resources by physical location or by type of machinery.

Constraints

A constraint is a type of condition set between two activities. Constraints are represented by arrowed polyline links.
Constraints can have one of the following types:

• start to start
• start to end
• end to start
• end to end
  
  

The source activity—that is, the activity whose start or end controls the start or end of another activity—is called the From activity. Conversely, the target activity—that is, the activity whose start or end depends on the start or end of another activity—is called the To activity.

Reservations

When a resource is assigned to an activity, this assignment is called a reservation. In the terminology of JViews Gantt, a reservation represents the assignment of one resource to one activity.
An activity can have multiple resources reserved and similarly, a resource can be reserved for more than one activity. The activity that reserves the resource cannot be changed after the reservation is created.