An apparatus for implementing "links" between objects or content items in applications or documents in a distributed system such that changes to the source objects or items are reflected in changes to the target objects or content items. The apparatus includes mechanisms for allowing users to establish links, to break individual links, to copy documents or content including links, and to determine locations and/or descriptions of the source of a given target or any or all of the multiple targets of a given source. Advantageously, the apparatus of this invention uses remote message passing for communication, thereby permitting links to be established even when the source and target applications execute on different platforms and even when they share no common file system. The apparatus includes an availability server which can serve as a surrogate for applications which are currently not running. This permits targets of links to query the state of a link source, to register/unregister with the link source in order to receive notification of updates, create new links linked to the same link source, and to break their link to the link source, even though the application containing the link source is unavailable. The apparatus of the availability server can be generalized to support the ability to support transparent access from one application to objects of a second application in the face of unavailability of the second application.