Extending and Relating Semantic Models of Compensating CSP

Business transactions involve multiple partners coordinating and interacting with each other. These transactions have hierarchies of activities which need to be orchestrated. Usual database approaches (e.g.,checkpoint, rollback) are not applicable to handle faults in a long running transaction due to interaction with multiple partners. The compensation mechanism handles faults that can arise in a long running transaction. Based on the framework of Hoare's CSP process algebra, Butler et al introduced Compensating CSP (cCSP), a language to model long-running transactions. The language introduces a method to declare a transaction as a process and it has constructs for orchestration of compensation. Butler et al also defines a trace semantics for cCSP. In this thesis, the semantic models of compensating CSP are extended by defining an operational semantics, describing how the state of a program changes during its execution. The semantics is encoded into Prolog to animate the specification. The semantic models are further extended to define the synchronisation of processes. The notion of partial behaviour is defined to model the behaviour of deadlock that arises during process synchronisation. A correspondence relationship is then defined between the semantic models and proved by using structural induction. Proving the correspondence means that any of the presentation can be accepted as a primary definition of the meaning of the language and each definition can be used correctly at different times, and for different purposes. The semantic models and their relationships are mechanised by using the theorem prover PVS. The semantic models are embedded in PVS by using Shallow embedding. The relationships between semantic models are proved by mutual structural induction. The mechanisation overcomes the problems in hand proofs and improves the scalability of the approach

Hierarchical models for service-oriented systems

We present our approach to the denotation and representation of hierarchical graphs: a suitable algebra of hierarchical graphs and two domains of interpretations. Each domain of interpretation focuses on a particular perspective of the graph hierarchy: the top view (nested boxes) is based on a notion of embedded graphs while the side view (tree hierarchy) is based on gs-graphs. Our algebra can be understood as a high-level language for describing such graphical models, which are well suited for defining graphical representations of service-oriented systems where nesting (e.g. sessions, transactions, locations) and linking (e.g. shared channels, resources, names) are key aspects

An Algebra of Hierarchical Graphs and its Application to Structural Encoding

We define an algebraic theory of hierarchical graphs, whose axioms characterise graph isomorphism: two terms are equated exactly when they represent the same graph. Our algebra can be understood as a high-level language for describing graphs with a node-sharing, embedding structure, and it is then well suited for defining graphical representations of software models where nesting and linking are key aspects. In particular, we propose the use of our graph formalism as a convenient way to describe configurations in process calculi equipped with inherently hierarchical features such as sessions, locations, transactions, membranes or ambients. The graph syntax can be seen as an intermediate representation language, that facilitates the encodings of algebraic specifications, since it provides primitives for nesting, name restriction and parallel composition. In addition, proving soundness and correctness of an encoding (i.e. proving that structurally equivalent processes are mapped to isomorphic graphs) becomes easier as it can be done by induction over the graph syntax

The Total Takings Myth

For almost thirty-five years, the U.S. Supreme Court has attempted to carve out a total takings doctrine within its regulatory takings jurisprudence. Most regulatory takings claims are evaluated under the “ad hoc” threefactor test first articulated in Penn Central Transportation Co. v. City of New York. Exceedingly few of these claims are successful. But the Court has identified certain categories of government actions that are compensable takings per se, otherwise known as total takings. This began in 1982 with Loretto v. Teleprompter Manhattan CATV Corp., where the Court held that a land use ordinance requiring a landowner to endure a permanent physical occupation of a portion of her property is always a compensable taking. Ten years later, in Lucas v. South Carolina Coastal Council, the Court held that a land use restriction depriving an owner of all economically viable use of her property is also compensable per se. Finally, in 2015, in Horne v. Department of Agriculture, the Court extended its total takings jurisprudence to personal property, announcing that the government appropriation of personal property is a per se compensable taking. Although the Court has had more than three decades to articulate theoretical justifications for its total takings jurisprudence and to provide guidance for lower courts in determining when a regulation constitutes a total taking, it has failed to do so. This failure reflects the underlying reality that the total takings doctrine is a myth. More particularly, the categories that the Court has identified as constituting total takings are analytically incoherent, and the terms the Court has used to demarcate total takings from regulations that are not per se compensable cannot be applied in the real world. As a result, lower courts struggle to apply the total takings doctrine and the case law remains in utter disarray. In fact, lower courts have resorted to creating “shadow” total takings doctrines that rely on obvious distortions of the plain meaning of outcome-determinative terms and deflect attention from the fundamental question of whether compensation is warranted. This Article argues that the Court’s attempt to create a total takings doctrine has failed, and that the Court should repudiate it. It demonstrates that the Court’s initial total takings opinions were conceptually incoherent and woefully undertheorized. And it shows that attempts by lower courts to rehabilitate the doctrine by crystallizing the bright-line rules through careful and consistent application were doomed to, and did, fail. This Article also explains why the entire enterprise was misguided from the start. Although bright-line rules have their place, it is not in the heart of regulatory takings doctrine, which is premised on concerns for fairness and justice in distributing the burdens of land use regulation. Last term, the Court had a perfect opportunity to begin the process of repudiating the total takings myth. Murr v. Wisconsin was a run-of-the-mill regulatory takings case masquerading as a Lucas-type total takings claim, and it presented the Court with a vehicle to either remedy the central doctrinal incoherence of Lucas’s bright-line rule or to overrule Lucas and turn its attention to the much needed task of clarifying and refining the Penn Central test. Instead, by offering a new multifactored test in a sort of regulatory takings “step zero,” the Court in Murr merely exacerbated the core flaws of the Lucas bright-line rule. Now, more than ever, it is imperative that the Court recognize and begin to dismantle the total takings myth

Activity diagrams: a formal framework to model business processes and code generation

Activity Diagram is an important component of the set of diagrams used in UML. The OMG document on UML 2.0 proposes a Petri net based semantics for Activity Diagrams. While Petri net based approach is useful and interesting, it does not exploit the underlying inherent reactive behaviour of activity diagrams. In the first part of the paper, we shall capture activity diagrams in synchronous language framework to arrive at executional models which will be useful in model based design of software. This also enables validated code generation using code generation mechanism of synchronous language environments such as Esterel and its programming environments. Further, the framework leads to scalable verification methods. The traditional semantics proposed in OMG standard need enrichment when the activities are prone to failure and need compensating actions. Such extensions are expected to have applications in modelling complex business processes. In the second part of the paper, we propose an enrichment of the UML Activity Diagrams that include compensable actions. We shall use some of the foundations on Compensable Transactions and Communicating Sequential Processes due to Tony Hoare. This enriched formalism allows UML Activity Diagrams to model business processes that can fail and require compensating actions