Vertical Implementation

We investigate criteria to relate specifications and implementations belonging to conceptually different levels of abstraction. For this purpose, we introduce the generic concept of a vertical implementation relation, which is a family of binary relations indexed by a refinement function that maps abstract actions onto concrete processes and thus determines the basic connection between the abstraction levels. If the refinement function is the identity, the vertical implementation relation collapses to a standard (horizontal) implementation relation. As desiderata for vertical implementation relations we formulate a number of congruence-like proof rules (notably a structural rule for recursion) that offer a powerful, compositional proof technique for vertical implementation. As a candidate vertical implementation relation we propose vertical bisimulation. Vertical bisimulation is compatible with the standard interleaving semantics of process algebra; in fact, the corresponding horizontal relation is rooted weak bisimulation. We prove that vertical bisimulation satisfies the proof rules for vertical implementation, thus establishing the consistency of the rules. Moreover, we define a corresponding notion of abstraction that strengthens the intuition behind vertical bisimulation and also provides a decision algorithm for finite-state systems. Finally, we give a number of small examples to demonstrate the advantages of vertical implementation in general and vertical bisimulation in particular.\u

FIR Filter Implementation by Efficient Sharing of Horizontal and Vertical Common Sub-expressions

No abstract availabl

An Antitrust Analysis of the Case for Wireless Network Neutrality

The ongoing debate about possible implementation of regulatory rules requiring “network neutrality” for wireless telecommunications services is inherently about whether to impose a prohibition on the ability of network operators to control their vertical relationships. Antitrust analysis is well suited to analyze whether a wireless network neutrality rule is socially beneficial. Implementing network neutrality rules would be akin to using a per se antitrust rule regarding vertical relationships instead of the rule of reason analysis typically applied to vertical relationships in antitrust. Per se rules are used to prevent actions that rarely, if ever, have any pro-competitive benefits, such as price-fixing agreements. Rule of reason analysis is used when there are potential efficiency gains from the actions under investigation. Some vertical practices of the wireless carriers, such as bandwidth restrictions, may appear to be anticompetitive, but may also have plausible efficiency justifications so should be judged under rule of reason analysis. Economic examination of the wireless industry shows significant competition between networks which reduces the concern about vertical relationships, but some areas that should be monitored by antitrust and regulatory authorities. We propose several regulatory changes that would likely increase wireless competition and lessen the perceived need for prophlactic network neutrality rules while at the same time allowing efficiency-enhancing vertical relationships.network neutrality, wireless internet, antitrust,

Software (Re-)Engineering with PSF III: an IDE for PSF

We describe the design of an integrated development environment (IDE) for PSF. In the software engineering process we used process algebra in the form of PSF for the specification of the architecture of the IDE. This specification is refined to a PSF specification of the IDE system as a ToolBus application, by applying vertical and horizontal implementation techniques. We implemented the various tools as specified and connected them with a ToolBus script extracted from the system specification