True Concurrency in Long-running Transactions for Digital Ecosystems

Abstract

The concept of a digital ecosystem (DE) has been used to explore scenarios in which multiple online services and resources can be accessed by users without there being a single point of control, which can be used to effectively serialise their interactions. We argue in this paper that this weak coupling between services places additional demands on the modelling of compensation and recovery management in long-running transactions over traditional SOC related formalisms. We describe an adaptation of Shields' vector languages, in that the synchronisation constraint is removed (no shared actions), as a formal semantics for a transaction in terms of the common ordering constraints on the underlying interactions between its participants. The notation afforded by the so-called transaction languages captures the invocations on each participant service (online resource), and at each point during execution, across the whole transaction. Concurrency is modelled explicitly through a notion of independence, which is lifted onto tuples of sequences (one for each participant of the transaction) rather than individual sequences, as in Mazurkiewicz trace languages or events, as in the event structures model. Participating subcomponents execute concurrently and failure of one or more causes the recovery of the whole transaction. Compensations are triggered immediately upon failure and concurrent forward actions are compensated concurrently. We highlight the benefits of our true-concurrent approach in the context of DEs and outline connections of transaction languages to other partial order models. Further, we discuss how our approach supports forward recovery in that recovering the whole transaction is avoided wherever possible.

Service Choreography, SBVR, and Time

“…In view of that example, it seems appropriate to look into expressing ordering of Fact Types in SBVR without changing the OMG standard or introducing special primitives particular to our approach. The idea is to express ordering in terms of dependency between certain messages (causality), and by implication also choice (conflict) and concurrency, which should be possible, especially if a true concurrency semantics is pursued as done in [22].…”

“…In the context of service choreography, verification additionally comes in the form of conformance and realisation [33,5]. Moreover, if choreographies are to be equipped with transactional guarantees [22], meaning that a series of compensations are performed upon failure, the ordering of the interactions is doubly important.…”

SBVR2Alloy: An SBVR to Alloy Compiler

“…Compensating behaviour is beyond the scope of the current paper. We refer the interested reader to work in [27], [28] on web transactions and the work in [16] on providing transactional guarantees to service interactions in the absence of a central coordinator.…”

“…Like UML design models it provides user-friendly graphical notations but these often exhibit various divergent semantics. UML collaboration diagrams [14] and UML 2 sequence diagrams [15], [16] have also been proposed, but drawing the diagrams typically requires integration with a UML tool.…”

“…Work on formal semantics in this area has focused more on the imperative (or procedural) approach [14], [17], [18], [19], [20], [21], [16], [22] and has been geared towards an interleaving semantics which sometimes unnecessarily restricts the possible behaviours, e.g., see PROPANE in [20], or forces the modeller into making premature decisions, e.g., see separated collaboration diagrams [14]. A true concurrency semantics is proposed in [16].…”