Book Chapters

Almeida PS, Moreno CB, Fonte V.  2007.  Improving on version stamps. On the Move to Meaningful Internet Systems 2007: OTM 2007 Workshops. 4806:1025–1031. Abstract

Optimistic distributed systems often rely on version vectors or their variants in order to track updates on replicated objects. Some of these mechanisms rely on some form of global configuration or distributed naming protocol in order to assign unique identifiers to each replica. These approaches are incompatible with replica creation under arbitrary partitions, a typical operation mode in mobile or poorly connected environments. Other mechanisms assign unique identifiers relying on statistical correctness. In previous work we have introduced an update tracking mechanism that overcomes these limitations. This paper presents results from recent experimentation, that brought to surface a particular pattern of operation that results in an unforeseen, unlimited growth in space consumption. We also describe informally a new update tracking mechanism that does not exhibit this pathological growth while providing guaranteed unique identifiers for a dynamic number of replicas under arbitrary partitions and the same functionality of version vectors.

Noble J, Vitek J, Lea D, Almeida PS.  1999.  Aliasing in object oriented systems. Object-Oriented Technology ECOOP’99 Workshop Reader. :793–793. Abstract

This chapter contains summaries of the presentations given at the Intercontinental Workshop on Aliasing in Object-Oriented Systems (IWAOOS’99) at the European Conference on Object-Oriented Programming (ECOOP’99) which was held in Lisbon, Portugal on June 15, 1999.

Almeida PS.  1997.  Balloon types: Controlling sharing of state in data types. ECOOP'97—Object-Oriented Programming. :32–59. Abstract

Current data abstraction mechanisms are not adequate to control sharing of state in the general case involving objects in linked structures. The pervading possibility of sharing is a source of errors and an obstacle to language implementation techniques.
We present a general extension to programming languages which makes the ability to share state a first class property of a data type, resolving a long-standing flaw in existing data abstraction mechanisms.
Balloon types enforce a strong form of encapsulation: no state reachable (directly or transitively) by a balloon object is referenced by any external object. Syntactic simplicity is achieved by relying on a non-trivial static analysis as the checking mechanism.
Balloon types are applicable in a wide range of areas such as program transformation, memory management and distributed systems. They are the key to obtaining self-contained composite objects, truly opaque data abstractions and value types—important concepts for the development of large scale, provably correct programs.