Determining How an Entity Should Be Stored › Guidelines for Determining How an Entity Should Be Stored › Is This Entity Both a Parent and a Child? › Is There Optimal Relationship Clustering for This Entity?

Is There Optimal Relationship Clustering for This Entity?

If the entity is involved in multiple relationships in which it is both the parent and child, it may be possible to cluster this entity around another related entity. Optimal clustering means that application programs access this entity most often in conjunction with another entity and clustering can be used effectively.

Clustering through a relationship is one of the most effective ways of reducing I/Os when related entity occurrences are retrieved together. Therefore, if applications accessing this entity frequently access related entities, you should generally cluster the child entities through the relationship.

Note: If the size of all clustered entity occurrences is too large, the benefit of clustering might be negated because several I/Os are required to access the entire cluster.

If there is no optimal clustering, the entity should be stored CALC, providing both an alternate entry point into the database and a parent around which other entities can be clustered.

Example

An example of such an entity is the EMPLOYEE entity. This entity is both a parent and a child but has no optimal clustering.

The COVERAGE entity, on the other hand, is both a parent and child but can be clustered optimally around the EMPLOYEE-COVERAGE relationship since access is most often by means of the EMPLOYEE entity, and multiple COVERAGE entity occurrences relating to a particular employee are often accessed at the same time.