This is the foreign key relating to the SavedSearch resource. A unique identifier for this record from the immediate source. This is a string that can include URI or other forms. Alternatively use the SavedSearchKeyNumeric for a numeric only key field. This is the local key of the system. When records are received from other systems, a local key is commonly applied. If conveying the original keys from the source or originating systems, see SourceSystemKey and OriginatingSystemKey variants.