Dynamic Condition Response Graphs Research Articles

Safe design and evolution of smart contracts using dynamic condition response graphs to model generic role‐based behaviors

Safe design and evolution of smart contracts using dynamic condition response graphs to model generic role‐based behaviors

Proactive enforcement of provisions and obligations

We present an approach to the proactive enforcement of provisions and obligations, suitable for building policy enforcement mechanisms that both prevent and cause system actions. Our approach encompasses abstract requirements for proactive policy enforcement, a system model describing how enforcement mechanisms interact with and control target systems, and concrete policy languages and associated enforcement mechanisms. As examples of policy languages, we consider finite automata and timed dynamic condition response (DCR) graphs. We use finite automata to illustrate the basic principles and DCR graphs to show how these principles can be adapted to a practical, real-time policy language. In both cases, we show how to algorithmically determine whether a given policy is enforceable and, when this is the case, construct an associated enforcement mechanism. Our approach improves upon existing formalisms in two ways: (1) we exploit the target system’s existing functionality to avert policy violations proactively, rather than compensate for them reactively; and (2) rather than requiring the manual specification of remedial actions in the policy, we deduce required actions directly from the policy.

Assured automatic dynamic reconfiguration of business processes

In order to manage evolving organisational practice and maintain compliance with changes in policies and regulations, businesses must be capable of dynamically reconfiguring their business processes. However, such dynamic reconfiguration is a complex, human-intensive and error prone task. Not only must new business process rules be devised but also, crucially, the transition between the old and new rules must be managed.In this paper we present a fully automated technique based on formal specifications and discrete event controller synthesis to produce correct-by-construction reconfiguration strategies. These strategies satisfy user-specified transition requirements, be they domain independent – such as delayed and immediate change – or domain specific. To achieve this, we provide a discrete-event control theoretic approach to operationalise declarative business process specifications, and show how this can be extended to resolve reconfiguration problems. In this way, given the old and the new business process rules described as Dynamic Condition Response Graphs, and given the transition requirements described with linear temporal logic, the technique produces a control strategy that guides the organisation through a business process reconfiguration ensuring that all transition requirements and process rules are satisfied. The technique outputs a reconfiguration DCR whose traces reproduce the controller’s reconfiguration strategy. We illustrate and validate the approach using realistic cases and examples from the BPM Academic Initiative.

Replication, refinement & reachability: complexity in dynamic condition-response graphs

We explore the complexity of reachability and run-time refinement under safety and liveness constraints in event-based process models. Our study is framed in the DCR $$^\star $$ process language, which supports modular specification through a compositional operational semantics. DCR $$^\star $$ encompasses the “Dynamic Condition Response (DCR) graphs” declarative process model for analysis, execution and safe run-time refinement of process-aware information systems; including replication of sub-processes. We prove that event-reachability and refinement are np-hard for DCR $$^\star $$ processes without replication, and that these finite state processes recognise exactly the languages that are the union of a regular and an $$\omega $$ -regular language. Moreover, we prove that event-reachability and refinement are undecidable in general for DCR $$^\star $$ processes with replication and local events, and we provide a tractable approximation for refinement. A prototype implementation of the DCR $$^\star $$ language is available at http://dcr.tools/acta16 .

Declarative event based models of concurrency and refinement in psi-calculi

Psi-calculi constitute a parametric framework for nominal process calculi, where constraint based process calculi and process calculi for mobility can be defined as instances. We apply here the framework of psi-calculi to provide a foundation for the exploration of declarative event-based process calculi with support for run-time refinement. We first provide a representation of the model of finite prime event structures as an instance of psi-calculi and prove that the representation respects the semantics up to concurrency diamonds and action refinement. We then proceed to give a psi-calculi representation of Dynamic Condition Response Graphs, which conservatively extends prime event structures to allow finite representations of (omega) regular finite (and infinite) behaviours and have been shown to support run-time adaptation and refinement. We end by outlining the final aim of this research, which is to explore nominal calculi for declarative, run-time adaptable mobile processes with shared resources.

Concurrency Models with Causality and Events as Psi-calculi

Psi-calculi are a parametric framework for nominal calculi, where standard calculi are found as instances, like the pi-calculus, or the cryptographic spi-calculus and applied-pi. Psi-calculi have an interleaving operational semantics, with a strong foundation on the theory of nominal sets and process algebras. Much of the expressive power of psi-calculi comes from their logical part, i.e., assertions, conditions, and entailment, which are left quite open thus accommodating a wide range of logics. We are interested in how this expressiveness can deal with event-based models of concurrency. We thus take the popular prime event structures model and give an encoding into an instance of psi-calculi. We also take the recent and expressive model of Dynamic Condition Response Graphs (in which event structures are strictly included) and give an encoding into another corresponding instance of psi-calculi. The encodings that we achieve look rather natural and intuitive. Additional results about these encodings give us more confidence in their correctness.

Contracts for cross-organizational workflows as timed Dynamic Condition Response Graphs

We conservatively extend the declarative Dynamic Condition Response (DCR) Graph process model, introduced in the PhD thesis of the second author, to allow for discrete time deadlines. We prove that safety and liveness properties can be verified by mapping finite timed DCR Graphs to finite state transition systems. We exemplify how deadlines can introduce time-locks and deadlocks and violate liveness. We then prove that the general technique for safe distribution of DCR Graphs provided in previous work can be extended to timed DCR Graphs. We exemplify the use of timed DCR Graphs and the distribution technique in praxis on a timed extension of a cross-organizational case management process arising from a previous case study. The example shows how a timed DCR Graph can be used to describe the global contract for a timed workflow process involving several organizations, which can then be distributed as a network of communicating timed DCR Graphs describing the local contract for each organization.

Declarative Event-Based Workflow as Distributed Dynamic Condition Response Graphs

We present Dynamic Condition Response Graphs (DCR Graphs) as a declarative, event-based process model inspired by the workflow language employed by our industrial partner and conservatively generalizing prime event structures. A dynamic condition response graph is a directed graph with nodes representing the events that can happen and arrows representing four relations between events: condition, response, include, and exclude. Distributed DCR Graphs is then obtained by assigning roles to events and principals. We give a graphical notation inspired by related work by van der Aalst et al. We exemplify the use of distributed DCR Graphs on a simple workflow taken from a field study at a Danish hospital, pointing out their flexibility compared to imperative workflow models. Finally we provide a mapping from DCR Graphs to Buchi-automata.

Contracts as Dynamic Condition Response Graphs

Contracts as Dynamic Condition Response Graphs