The two types of relationships between object classes that are indicated by association classes are relationship by the same key property and relationship by different key properties.

Some association classes have a master-slave relationship (Weak association).

This section describes the relationships between object classes that are indicated by association and weak association.

• Relationship by the same key property
  For example, the association class HardwareLink indicates the relationship between asset information AssetInfo and hardware information HardwareInfo. The key property of both object classes is AssetID.
  Because AssetInfo and HardwareInfo always have a one-to-one correspondence, the relationship between these two object classes can be represented by AssetID.
  For this reason, information defining the relationship between AssetInfo and HardwareInfo (association class information) is not created in the asset management database.
  The figure below shows the relationship between object classes that is represented by HardwareLink.
  

  Figure 8-3 Relationship by the same key property

  

• Relationship by the different key properties
  For example, the association class ContractLeaseLink indicates the relationship between contract information Contract and asset information AssetInfo. Their key properties are ContractID and AssetID, which are not the same.
  This is because when multiple devices are contracted as a group, multiple AssetInfos are associated with a single Contract.
  In the asset management database, information defining the relationship between two object classes is created (as an association class) using different key properties.
  The figure below shows the relationship between the object classes represented by ContractLeaseLink:
  

  Figure 8-4 Relationship by different key properties

  

• Master-slave relationship (weak association)
  Two different classes are represented by a master-slave relationship. In this relationship, deleting the master class automatically deletes the slave class (weak class).
  HardwareLink is an example of an association class that indicates a master-slave relationship. When the asset is hardware, the asset information class AssetInfo is associated with the hardware asset class HardwareInfo. This means that there is an asset, and that it has hardware information as its additional information. Therefore, AssetInfo is the master class and this master class has a weak association with HardwareInfo, which is the slave class.
  For details about the master-slave relationship between object classes, see 14.1.3 Relationships between classes.