If a [[MetaProxyProperty]] related to a [[MetaProxy]] is configured to be a an '''ExternalPrimaryKey''' {{UBIK}} will handle this property of the corresponding [[Proxy]] object as an '''external key property'''.
== Feature ==Such properties provide the following features:It is possible to search for * Proxy objects can be searched by their external key property;* Proxy objects can be linked to each other by using their external key properties and an external reference.
It is possible to create links between proxy objects by using their external key properties and an external reference. == External Reference reference ==An external Reference reference is a link to a Proxy instance via a property valuesvalue. If the ProxyMetaProperty MetaProxyProperty has a defined Reference it is defined as an External Reference. The Proxy will refer automatically to the instance of the targeted MetaProxy having the same entry in its external Primary Key Property than the given Proxy instance.
{{Hint|When using external keys and external references it does not matter which object is created first (master or child), the linkage will be done!}}
