Affine Sessions

Session types describe the structure of communications implemented by channels. In particular, they prescribe the sequence of communications, whether they are input or output actions, and the type of value exchanged. Crucial to any language with session types is the notion of linearity, which is essential to ensure that channels exhibit the behaviour prescribed by their type without interference in the presence of concurrency. In this work we relax the condition of linearity to that of affinity, by which channels exhibit at most the behaviour prescribed by their types. This more liberal setting allows us to incorporate an elegant error handling mechanism which simplifies and improves related works on exceptions. Moreover, our treatment does not affect the progress properties of the language: sessions never get stuck

There are no universal rules for induction

In a material theory of induction, inductive inferences are warranted by facts that prevail locally. This approach, it is urged, is preferable to formal theories of induction in which the good inductive inferences are delineated as those conforming to universal schemas. An inductive inference problem concerning indeterministic, nonprobabilistic systems in physics is posed, and it is argued that Bayesians cannot responsibly analyze it, thereby demonstrating that the probability calculus is not the universal logic of induction. Copyright 2010 by the Philosophy of Science Association.All right reserved

CaSPiS: A Calculus of Sessions, Pipelines and Services

Service-oriented computing is calling for novel computational models and languages with well disciplined primitives for client-server interaction, structured orchestration and unexpected events handling. We present CaSPiS, a process calculus where the conceptual abstractions of sessioning and pipelining play a central role for modelling service-oriented systems. CaSPiS sessions are two-sided, uniquely named and can be nested. CaSPiS pipelines permit orchestrating the flow of data produced by different sessions. The calculus is also equipped with operators for handling (unexpected) termination of the partner’s side of a session. Several examples are presented to provide evidence of the flexibility of the chosen set of primitives. One key contribution is a fully abstract encoding of Misra et al.’s orchestration language Orc. Another main result shows that in CaSPiS it is possible to program a “graceful termination” of nested sessions, which guarantees that no session is forced to hang forever after the loss of its partner

PROPORTIONALITY: THE STRUGGLE FOR BALANCE IN U.S. IMMIGRATION POLICY†

In September 1957, Governor Orval Faubus dispatched Arkansas National Guard troops to prevent black students from entering Central High School in Little Rock, Arkansas. The Eisenhower Administration responded by sending Justice Department lawyers to enter school desegregation litigation brought by the NAACP that was already pending before the U.S. District Court in Arkansas. The court granted the preliminary injunction sought by the Justice Department and the NAACP, holding that federal law preempted state interference with school integration. A few weeks later, in the face of local resistance edged with hatred and violence, President Eisenhower ordered the famous 101st Airborne to Arkansas to maintain order and safeguard the black school children. The court\u27s injunction was upheld on appeal, and Central High was eventually desegregated. The most important legacy of the conflict, however, may have been the images from the streets of Little Rock–striking photographs of tense black students, sturdy federal troops, and a surging, spitting crowd of white protesters