abstract-les摘要-莱斯

Naftaly Minsky Rutgers University,On the Governance of Open Distributed Systems,N. Minsky, PUC Nov25/05,The phenomenon of Open Distributed Systems ,Computing is undergoing a transition from monolithic systems, constructed according to a single overall design, into open and irregular conglomerates of distributed components. The composition of such open system is changing dynamically, and largly unknown. Examples of open systems. Heterogeneous multi-agents systems, like sensor systems. Distributed Enterprises Coalitions of enterprises (e.g., grids, virtual enterprises),N. Minsky, PUC Nov25/05, and their Problematics,How does one design and built such systems, so that they would operate coherently as a whole? How does one ensure the security and fault tolerance of such systems? How can one reason about such systems?,N. Minsky, PUC Nov25/05,On Reasoning about Systems,The conventional approachaccording to a 2000 report by SEI of CMU, which views the key challenge facing Component-Based SE, the “holy grail”, they call it, as follows: “to ensure that the properties of a system of components can be predicted from the properties of the components themselves” . But in open systems the components are unknown so, the real challenge is: to reason about a system without knowing its details.,N. Minsky, PUC Nov25/05,Reasoning about Open Systems,We do it all the time We reason about the physical world, relying on the laws of nature; And about the social world, relying on social laws and norms. But, there are virtually no laws regulating distributed software systems.,N. Minsky, PUC Nov25/05,The “Governance” Approach,This approach- introduced in “The Imposition of Protocols Over Open Distributed Systems“, by Minsky, in IEEE Trans. on SE, 1991. -rests on the following simple observations: In the absence of natural laws of software, we need to formulate artificial laws, like we do for societies. Such laws need to be enforced, by preventing their violations, so they can be as dependable as laws of physics. The enforcement needs to be done in a decentralized fashion, for scalability.,N. Minsky, PUC Nov25/05,Potential Benefits of Laws, and their Pitfalls,The benefits They could engender predictabilitydespite the openness and heterogeneity of the system at handthus simplifying it. They could facilitate harmonious collaboration, and safe competition. They could provide protection against ignorant, careless, or malicious, agents. The Pitfalls: one can overregulate, or just formulate bad laws. “Law is order-good law is good order” Aristotle, in Politics Book 7.,N. Minsky, PUC Nov25/05,The Concept of Law-Governed Interaction (LGI),LGI is a message exchange mechanism that enables a community of distributed agents to interact under an explicit and strictly enforced policy, called the “law” of this community. Some characteristics of LGI: The law treats the agents regulated by it as black boxes, governing only their interaction; but it is sensitive to the history of their interaction. Laws are expressed locally, but they govern globally the entire community subject to them. A single system may have a multitude of interrelated laws, which may interoperate, and be hierarchically organized. Laws are enforced, in a decentralized manner.,N. Minsky, PUC Nov25/05,Centralized Enforcement of Communal Policies,* The problems: potential congestion, and single point of failure,* Replication does not help, if S changes rapidly enough,N. Minsky, PUC Nov25/05,Distributed Law-Enforcement under LGI,N. Minsky, PUC Nov25/05,Deployment of LGI,N. Minsky, PUC Nov25/05,Applicationsto Security and SE,Large and Heterogeneous agent systems, such as systems of sensors. In particular, ensuring their underlying protocols, and providing for fault tolerance. Mobile computing. Structuring distributed systems In particular, by providing for traditionally language based capabilities like scope rules and exception handling. Composition of Web Services.,N. Minsky, PUC Nov25/05,Applications (cont),Electronic commerce, particularly of the B2B type The management and distribution of medical records. Regulating entreprise systems Involves hierarchy of laws, and interoperability between them. Generalizing the concept of workflows Flexible regulation of dynamic coalitions As in grids, virtual enterprises, supply chains.,N. Minsky, PUC Nov25/05,Coalitions, and their Governance,Consider a coalition C of enterprises E1,., En, governed by a coalition-policy PC-where each Ei is governed by its own internal-policy Pi .,N. Minsky, PUC Nov25/05,The Main Issues,Enforcement of these policies, in a scalable and trustworthy manner. Ensuring that every interaction between xi /Ei and xj /Ej conforms to all three policies Pi , PC , Pj, which are to govern it? The flexible formulation of these policies, so that their specification and evolution would be manageable.,N. Minsky, PUC Nov25/05,A Principle of Flexible Policy Formulation,Each coalition member Ei should be able