Josva Kleist

I&C Journal 2002 Journal Article

Aliasing Models for Mobile Objects

• Uwe Nestmann
• Hans Hüttel
• Josva Kleist
• Massimo Merro

In Obliq, a lexically scoped, distributed, object-oriented programming language, object migration was suggested as the creation of a copy of the state of an object at the target site, followed by turning the object itself into an alias, also called surrogate, for the remote copy. We consider the creation of object surrogates as an abstraction of the above-mentioned style of migration. We introduce Øjeblik, a typed distribution-free subset of Obliq, and provide four different configuration-style semantics, which only differ in the respective aliasing model. We show that two of the semantics, one of which matches Obliq's implementation, render migration unsafe, while our new proposal allows for safe migration at least for a large class of program contexts. In addition, we propose a type system that allows a programmer to statically guarantee that programs belong to that class. Our work suggests a straightforward repair of Obliq's aliasing model.

I&C Journal 2002 Journal Article

Mobile Objects as Mobile Processes

• Massimo Merro
• Josva Kleist
• Uwe Nestmann

Obliq is a lexically scoped, distributed, object-based programming language. In Obliq, the migration of an object is proposed as creating a clone of the object at the target site, whereafter the original object is turned into an alias for the clone. Obliq has only an informal semantics, so there is no proof that this style of migration is safe, i. e. , transparent to object clients. In previous work, we introduced Ø, an abstraction of Obliq, where, by lexical scoping, sites have been abstracted away. We used Ø in order to exhibit how the semantics behind Obliq's implementation renders migration unsafe. We also suggested a modified semantics that we conjectured instead to be safe. In this paper, we rewrite our modified semantics of Ø in terms of the π-calculus, and we use it to formally prove the correctness of object surrogation, the abstraction of object migration in Ø.

I&C Journal 2002 Journal Article

Mobile Objects as Mobile Processes

• Massimo Merro
• Josva Kleist
• Uwe Nestmann