Two-way Associations

Mostly, associations are travel in both directions, although not usually with same frequency. There are three approaches for the implementation.

• In bi-directional associations, if one direction association is seldom used, then we should implement it as unidirectional association. Searching can perform reverse association. This way, we can reduce storage and update cost.
• Implementing it as a bi-directional association using the several techniques discussed in previous sections will turn up as shown in Figure. This approach provides faster access but also requires updating of other attributes in case of any change otherwise the link will become inconsistent.

Implementing it as a separate association object, i.e., independent of any class as shown in Figure. The association object can be implemented using two objects: one in forward direction and the other one in the reverse direction. This cause increases efficiency when hashing is used, instead of attribute pointer.

  Figure:  Implementation of association as an object