On Synchronous and Asynchronous Monitor Instrumentation for Actor-based systems

We study the impact of synchronous and asynchronous monitoring instrumentation on runtime overheads in the context of a runtime verification framework for actor-based systems. We show that, in such a context, asynchronous monitoring incurs substantially lower overhead costs. We also show how, for certain properties that require synchronous monitoring, a hybrid approach can be used that ensures timely violation detections for the important events while, at the same time, incurring lower overhead costs that are closer to those of an asynchronous instrumentation.Comment: In Proceedings FOCLASA 2014, arXiv:1502.0315

Improving Runtime Overheads for detectEr

We design monitor optimisations for detectEr, a runtime-verification tool synthesising systems of concurrent monitors from correctness properties for Erlang programs. We implement these optimisations as part of the existing tool and show that they yield considerably lower runtime overheads when compared to the unoptimised monitor synthesis.Comment: In Proceedings FESCA 2015, arXiv:1503.0437

Monitoring distributed systems with distributed polyLarva

polyLarva is a language-agnostic runtime verification tool, which converts a polyLarvaScript into a monitor for a given system. While an implementation for polyLarva exists, the language and its compilation have not been formalised. We therefore present a formal implementation-independent model which describes the behaviour of polyLarvaScript, comprising of the uLarvaScript grammar and of a set of operational semantics. This allows us to prove important properties, such as determinism, and also enables us to reason about ways of re-designing the tool in a more scalable way. We also present a collection of denotational mappings for uLarvaScript converting the constructs of our grammar into constructs of a formal actor-based model, thus providing an Actor semantics for uLarvaScript. We are also able to prove certain correctness properties of the denotational translation such as that the denoted Actors behave in a way which corresponds to the behaviour described by our implementation-independent model. We finally present distPolyLarva, a prototype implementation of the distributed polyLarva tool, which implements the new actor-based semantics over a language that can natively handle distribution and concurrency called Erlang.peer-reviewe

A study of the production structure of the Maltese economy : an input-output approach

This thesis presents a study of the production structure of the Maltese economy based on the input-output and social accounting matrix frameworks. This study provides an exhaustive analysis of the various interrelations which characterize the flow structure of production activities within the Maltese economy, as well as provides a framework in which it is possible to assess the behaviour, in terms of transactions and transfers, of all the economic agents which characterize the Maltese economic system. This thesis presents the construction of the first symmetric input-output for the Maltese economy, for the year 2000 which has a high level of sectoral disaggregation and which also conforms to both European system of accounts guidelines published in 1995 and the Eurostat input-output methodological guidelines. The constructed symmetric input-output table was subsequently employed for the compilation, via the construction of a set of income expenditure accounts, of the first fully articulated social accounting matrix for Malta for the year 2000. Via the application of input-output and social accounting matrix based linkages analysis a detailed study is carried out in order to assess the underlying inter-industry relations which characterize the flow structure of the Maltese economy. The results obtained also provide policy makers with a broad range of analytically derived estimates with which to evaluate the strategic importance of each industry within the context of the national economy

Estimates of input-output multipliers for the Maltese economy based on the symmetric input-output table for 2010

The study presents the estimates of industry specific multipliers which are derived utilizing a highly disaggregated symmetric input-output table for the Maltese Economy for 2010, published by the National Statistics Office of Malta in 2016. The aim of this study is to derive and analyse a set of output, value added, income and employment multipliers, which illustrate how an exogenous shock to the final demand of each industry would affect the production activities of the Maltese economy on the basis of the Leontief demand driven model. Both the open, as well as the closed Leontief demand driven model are utilized in order to derive the simple and total multipliers. The study presents a comparative analysis of the direct, indirect and induced multiplier effects in terms of the output, value added, income and employment generation for each industry within the Maltese economy. Although there is a considerable degree of heterogeneity in the results obtained across the various multiplier measures, when considering the complete set of multiplier results, a number of industries do feature as relatively strong performers across all categories of multipliers. The accommodation and food services activities feature in the top 15 in almost all categories of multipliers under consideration, confirming the historic tendency for the tourism sector to feature as a key important economic driver. The sectors associated with the public sector, more specifically the public administration, education and human health sectors, were also found to consistently exhibit relatively strong multiplier effects.peer-reviewe

Analysis of Input (Supply) Multipliers for the Maltese Economy on the Basis of the SIOTs for 2010 and 2015

The goal of this study is to present and assess estimates of input (supply) multipliers within the context of the Maltese economy to identify in which economic sectors it is the most beneficial to allocate primary resources with the aim to support economic growth. Via the application of the Ghoshian Supply-Driven Model, this study presents the first highly disaggregated input (supply) multiplier estimates for the Maltese economy based on the 2010 and 2015 Symmetric Input-Output Tables. This study also includes a comparative analysis between the years 2010 and 2015 to assess changes in the input (supply) multipliers ranking across economic sectors. Based on the 2015 Symmetric Input-Output Table, potential output is mostly increased following the additional allocation of primary inputs to the Manufacturing of other non-metallic mineral products sector following the highest input (supply) multiplier estimate, keeping all else constant. Furthermore, based on the 2010 Symmetric Input-Output Table, the Advertising and market research sector registered the highest input (supply) multiplier. The input (supply) multipliers are subject to the traditional input-output framework and the supply-side modelling assumptions. However, they do provide estimates on the potential change in economy-wide output following exogenous primary input shocks in every sector. In other words, the input (supply) multipliers provide policy makers a guide in which economic sector it is most beneficial to allocate primary inputs, such as labour supply, with the aim of supporting economic growth. The derived input (supply) multipliers may be utilised to aid in the formation of industry specific labour market policies with the aim of supporting overall economic expansion

On Runtime Enforcement via Suppressions

Runtime enforcement is a dynamic analysis technique that uses monitors to enforce the behaviour specified by some correctness property on an executing system. The enforceability of a logic captures the extent to which the properties expressible via the logic can be enforced at runtime. We study the enforceability of Hennessy-Milner Logic with Recursion (muHML) with respect to suppression enforcement. We develop an operational framework for enforcement which we then use to formalise when a monitor enforces a muHML property. We also show that the safety syntactic fragment of the logic, sHML, is enforceable by providing an automated synthesis function that generates correct suppression monitors from sHML formulas

Developing theoretical foundations for runtime enforcement

The ubiquitous reliance on software systems is increasing the need for ensuring their correctness. Runtime enforcement is a monitoring technique that uses moni- tors that can transform the actions of a system under scrutiny in order to alter its runtime behaviour and keep it in line with a correctness specification; these type of enforcement monitors are often called transducers. In runtime enforcement there is often no clear separation between the specification language describing the cor- rectness criteria that a system must satisfy, and the monitoring mechanism that actually ensures that these criteria are met. We thus aim to adopt a separation of concerns between the correctness specification describing what properties the sys- tem should satisfy, and the monitor describing how to enforce these properties. In this thesis we study the enforceability of the highly expressive branching time logic μHML, in a bid to identify a subset of this logic whose formulas can be adequately enforced by transducers at runtime. We conducted our study in relation to two different enforcement instrumentation settings, namely, a unidirectional setting that is simpler to understand and formalise but limited in the type of system actions it can transform at runtime, and a bidirectional one that, albeit being more complex, it allows transducers to effect and modify a wider set of system actions. During our investigation we define the behaviour of enforcement transducers and how they should be embedded with a system to achieve unidirectional and bidirectional enforcement. We also investigate what it means for a monitor to adequately enforce a logic formula, and define the necessary criteria that a monitor must satisfy in order to be adequate. Since enforcement monitors are highly intrusive, we also define a notion of optimality to use as a guide for identifying the least intrusive monitor that adequately enforces a formula. Using these enforcement definitions, we identify a μHML fragment that can be adequately enforced via enforcement transducers that drop the execution of certain actions. We then show that this fragment is maximally expressive, i.e., it is the largest subset that can be enforced via these type of enforcement monitors. We finally look into static alternatives to runtime enforcement and identify a static analysis technique that can also enforce the identified μHML fragment, but without requiring the system to execute