Concur: An Investigation of Lightweight Migration in Support of Centralized Synchronous Distributed Collaboration Public Deposited

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  • March 20, 2019
  • Menges, John Edward
    • Affiliation: College of Arts and Sciences, Department of Computer Science
  • Synchronous distributed collaborative systems support simultaneous observation of and interaction with shared objects by multiple, dispersed participants. Centralized architectures for such systems support simple user mental models and are comparatively easy to implement, but they suffer from high latency. Replicated architectures improve latency at the expense of more complex user mental models and implementations. Hybrid and dynamic architectures apply centralized and replicated sub-architectures in an attempt to get the best of both worlds, but in reality they further complicate implementations and user mental models. Concur is an architecture I developed to investigate lightweight migration as an alternative means to attain the best characteristics of centralized and replicated architectures. Previous dynamic architectures improved latency using the migration of heavyweight processes or (object-oriented) objects, which is costly in terms of migration time and runtime requirements. In Concur I have instead organized collaborative applications and supporting infrastructures around migrating entities which are not required to have full process or object semantics. These entities are classified by properties affecting migration, such as their size and their use of external references. In this way I achieved both the simpler user mental models and implementations of centralized systems and the superior latency characteristics of replicated systems. Concur accomplishes this through the fast migration of lightweight entities in a multi-centered centralized system, where a multi-centered system is defined as having single physical center and multiple, independently-migrating and entity-specific logical centers. This dissertation also identifies other significant advantages of the Concur architecture. Sub-object, easily-migratable entity classes minimize runtime requirements, facilitating widespread entity distribution. This in turn helps us to achieve the critical mass required for the success of any communication technology. The speed of lightweight entity migration also enables migrations to be triggered based on telegraphed user intentions (user actions that hint at imminent succeeding actions). I have demonstrated that telegraphed intentions are more accurate predictors of future interactions than the recent interaction histories considered in previous systems. Migrating entities based on these telegraphed intentions increases the probability that an entity will be located near a user when he begins to manipulate it.
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  • Jeffay, Kevin
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