Towards Next Generation Panel at SAINT 2002 Gul Agha Professor of Computer Science and Computational Science and Engineering University of Illinois at Urbana-Champaign http://www.osl.cs.uiuc.edu

Research Directions What are the programming models for Applications on the Internet? Massively parallel, distributed and mobile. Multi-agent Systems Actors Network Embedded Systems Integration of continuous and discrete processes.

Large Scale Actor Systems Reasoning about large-scale agent systems. Asynchrony: Autonomous agents that communicate asynchronously. Modularity: Concurrent components each with several agents. Locality and Non-interference: Message are the only means of information flow. Mobility: Reconfiguration and extension of systems.

Formal Methods Probabilistic reasoning about distributed and mobile real-time systems: Techniques for analysis of algorithms. Performance models. Models must account for: Stochastic duration of actions. Probabilistic behavior of node or system. Uncertainty in the environment.

Metrics for Large-Scale Systems Probabilities on evolution of system. Quantifying robustness, stability, timeliness, … Summations over execution paths for statistical metrics..

Models of Time Global synchronous wall clock Synchronization is too tight Too detailed an execution model Asynchronous, distributed time Vector clocks are too expensive Application behavior is complicated Need a more expressive model of time: Notion of distance and distribution. Space-Time cone of causal influence.

Past causally connected Causality and Time t Future causality R P Q Not Causally related x S Past causally connected y

Agents with Bounded Resources Each agent has bounded resources. Dynamic binding of agents to computational and network resources. Control of Multi-Agent Systems by bounding resources: Stability Efficiency Optimizing search Preventing denial of service attacks

Coordination Algorithms Large-scale systems where: Nodes and links have variable capabilities. Real-time requirements in the absence of a predefined global clock. Faults are common.

Example: Global Snapshot Consistent with causal relations. Real-time constraints: Duration of snapshot “skew”. Completion time of snapshot. Scalable Minimize number of messages. Dynamic topology of nodes and channels. Notion of approximation in snapshots: Farther apart nodes have larger skews.

New Directions Hybrid Systems More complex middleware Network Embedded Systems More complex middleware Naming Computational Reflection World-Wide Computer Mobility Grid-based computing