Thor is a distributed object-oriented database where objects are stored persistently at highly-available servers called object repositories, or ORs. In a large Thor system, performance tuning and system reconfiguration dictate that objects must be able to migrate among ORs. The paper describes two schemes for object references that support object migration, one using location-independent names and the other, location-dependent names. The paper analyzes the performance of the two schemes and concludes that location-dependent names are the right choice for systems like Thor, where we want fast access to objects that have migrated. Categories and Subject Descriptors: H.2.4 [Database Management]: Systems: Distributed systems; C.2.4 [Computer-Communication networks]: Distributed Systems --- Distributed databases; D.4.7 [Operating Systems]: Organization and Design --- Distributed systems; E.2 [Data Storage Representations]: Linked representations; H.2.2 [Database Management]: Physical Desig..