Abstract: Two locking protocols are defined for distributed database systems. One protocol provides deadlock avoidance without the need to roll back transactions. The other allows a useful weakening of the protocol in which only a limited class of easily handled deadlocks may occur. The protocols are capable of handling replicated as well as partitioned data. Like the centralized protocol on which they are based, the protocol of this paper permits locking at multiple granularities and allows collections of locks to be constructed to correspond to an arbitrary collection of database operations. Special provisions are made in the protocol to allow readers, and in particular, readers that touch data at only one site, to execute with less locking overhead than writers. Following the description of the protocol, comparisons are made between the protocol of this paper and other protocols previously published that offer similar features.

Abstract: This paper presents a model for the description of communication protocol in view of the total behavior of terminal equipment. In this model, a protocol entity is modeled as a group of processes and monitors, and synchronization between input and output processes is represented by the synchronizing mechanism based on the concept of the monitor. Furthermore, it is possible to specify the relation between entities of different layers of the protocol, including the relation between communication and local functions of terminal equipment. As an example of protocol description based on this model, TELETEX document layer protocol written in concurrent PASCAL language is illustrated.

Abstract: Communications protocols are crucial for the reliable exchange of information in distributed systems. In this dissertation, we consider the problem of formally specifying and verifying properties of protocol systems. Such systems are modeled by hierarchies of concurrent processes, where interprocess communication is achieved by message passing rather than through arbitrary shared variables. Based on this model, a methodology is developed for mechanically assisted protocol analysis. The Gypsy methodology for concurrent program verification is the point of departure for much of this work. Specialized methods applicable to protocols are derived from the Gypsy methods. Behavior of protocol modules is specified in a fairly abstract manner using a state transition paradigm, thus avoiding a highly procedural form of specification. Protocol services are specified by means of assertions over message histories. Proof techniques are introduced for verifying safety properties of the process models. In addition, a specification and assertion language is developed. This language emphasizes features and operations useful for expressing protocol oriented concepts and constructing proofs about them. An important aspect of this work is use of machine assisted analysis, most notably the use of mechanical theorem proving. A strategy for applying a particular automatic theorem prover, the Boyer-Moore prover, to protocol verification problems is put forth. A consequence of this strategy is the accumulation of a large body of proved lemmas, constituting a rudimentary deductive theory for protocols. With this theory, the methodology has successfully been applied to a pair of sample transport protocols. These include the Stenning protocol and an abstraction of the data transfer function of TCP.