Types of links
Each type of link indicates a different relationship between two units, and each type of link has different rules. Refer to the individual topics on each type of link for more information.
Links are directional; they have a source unit and a target unit. When creating the link, you first indicate the source of the link and create the link to the target unit. In most cases, the direction of the link is relevant; for example, you cannot switch the source and target of a dependency link because this type of link always goes from a requirement to a capability, never from a capability to a requirement. However, in some cases, the direction of the link is not relevant, as with colocation constraint links; in this case, the link has the same meaning if the source and target units are switched.
- Hosting link
- A hosting link indicates that the source unit is hosted on the target unit; that is, that the source unit is installed on or runs on the target unit.
- Realization link
- A realization link indicates that the target unit is the specific representation of the characteristics described by the source unit.
- Dependency link
- A dependency link indicates that the source unit depends on the target unit in a peer relationship.
- Membership link
- A membership link indicates that the target unit contains the source unit.
- Constraint link
- A constraint link between two units indicates a limitation on
the relationship between those units. The following types of constraint
links are available:
- Anti-Colocation
- Specifies that the two units cannot be hosted on the same hosting stack.
- Application Communication
- Specifies that the two units must be able to communicate.
- Attribute Propagation
- Specifies that a specified attribute, such as an attribute on a requirement or capability, must have the same value on the source unit and the target unit.
- Colocation
- Specifies that the two units must be hosted on the same hosting stack.
- Deferred Hosting
- Specifies that the source unit must be hosted on the target unit or the realization of that target unit, but not necessarily directly.
- Deploy Order
- Specifies that automated tasks on the target unit must run before, after, or not at the same time as the source unit. This constraint is meaningful only when you use topologies to automate tasks as described in Automating deployment tasks.
- Network Communication
- Specifies that the two units must have access to each other over the network.
- Redundancy
- Specifies that the target unit is a backup or replacement for the source unit.
- Resource Capacity Planning
- Ensures that the target unit has sufficient resources to host the source unit.