The Realization relationship links a logical entity with a more concrete entity that realizes it.
The Realization relationship indicates how logical entities ("what" or "logical"), such as services, are realized by means of more concrete entities ("how" or "physical").
A Business Process or Function may realize a Service. A Data Object may realize a Business Object. An Artifact may realize an Application Component. A core element may realize a Motivation element.
An Application Component, "Financial Application", realizes a "Billing" Service.
A "Billing" Data Object realizes the Business Object, "Invoice".