The evidence relationship entity manages relationships between business entities. These relationships are normally referred to as parent child relationships and can exist for a number of reasons. One such reason is where the parent is the main business entity and the child provides further details, the further details being separated into a separate entity because there's potentially more than one occurrence. For example income and income usage has a parent child relationship as the income usage provides more information about income evidence and there may be more than one usage of income at any one point in time.

Another reason for a relationship between two evidence types is where one aspect of the evidence is optional and this information may also be used elsewhere in a different context i.e. with a different business entity. For example a client takes out a loan, the loan may be used for property repairs and therefore a relationship is created between the loan and the property. However the property could exist for the client anyway and there may never be a loan associated with it.