Formal Specification and Automatic Verification of Multi-Agent Conditional Commitments and their Applications

Modeling agent communication using social commitments in the form of obligatory contracts among intelligent agents in a multi-agent system (MAS) provides a quintessential basis for capturing flexible and declarative interactions and helps in addressing the challenge of ensuring compliance with specifications. However, on the one hand, social commitments exclusively are not able to model agent communication actions, the cornerstone of the fundamental agent communication theory, namely speech act theory. These actions provide mechanisms for dynamic interactions and enable designers to track the evolution of active commitments. On the other hand, the designers of the system cannot guarantee the emergence of expected behaviors, such as self-contained intelligent agent complies with its protocols and honors its activated commitments. Moreover, the designers might still wish to develop effective and scalable algorithms to tackle the problem of model checking complex interactions modeled by conditional commitments and conditional commitment actions and regulated by commitment-based protocols at design time. Conditional commitments are a natural and universal frame of social commitments and cope with business conditional contracts. This dissertation is in principle about addressing two open challenging issues: 1) formally defining computationally grounded semantics for agent communication messages in terms of conditional commitments and associated actions (fulfill, cancel, release, assign and delegate), which is yet to be studied; and 2) developing a symbolic algorithm dedicated to tackle the raised model checking problem and to ensure the development of correct systems. In this dissertation, we start with distinguishing between two types of conditional commitments: weak and strong. Weak conditional commitments are those that can be activated even if the antecedents will never be satisfied, while strong conditional commitments are those that can be solely activated when there is at least one possibility to satisfy their assigned antecedents. We develop a branching-time temporal logic called CTL{cc,\alpha} that extends computation tree logic (CTL) with new modalities for representing and reasoning about the two types of conditional commitments and their actions using the formalism of interpreted systems. We present a set of valid properties, a set of reasoning rules, and a set of action postulates in order to explore the capabilities of CTL{cc,\alpha}. Furthermore, we propose a new life cycle of conditional commitments. Having a new logic (CTL{cc,\alpha}), we introduce a new symbolic algorithm to tackle the problem of its model checking. Instead of developing our algorithm from scratch, we extend the standard CTL model checking algorithm with symbolic algorithms needed for new modalities. We also investigate important theoretical results (soundness and termination) of the algorithm. Given that, we completely implement our algorithm and then assemble it on top of the symbolic model checker MCMAS, developed to automatically and directly test MAS specifications. The resulting symbolic model checker is so-called MCMAS+. We extend MCMAS's input modeling and encoding language called ISPL with shared and unshared variables needed for agent interactions and with the syntactic grammar of new modalities to produce a new one called ISPL+. We also extend the MCMAS's graphical user interface to display verified models to reduce inefficient and labor-intensive processes performed by the designers. To evaluate the performance of the developed algorithm, we analyze its time and space computational complexity. The computed time and space complexity are P-complete for explicit models and PSPACE-complete for concurrent programs. Such results are positive because model checking CTL{cc,\alpha} has the same time and space complexity of model checking CTL although CTL{cc,\alpha} extends CTL. Therefore, CTL{cc,\alpha} balances between expressive power and verification efficiency. Regarding the feasibility aspect, we apply our approach in three different application domains: business interaction protocols, health care processes, and web service compositions. The MAS paradigm is successfully employed in these domains wherein a component is represented, implemented and enacted by an agent. The proposed approach improved the employed MAS paradigm by formally modeling and automatically verifying interactions among participating agents so that the bad behaviors can be detected and then eliminated or repaired at design time and the confidence on the safety, efficiency and robustness is increased. We conduct extensive experiments to evaluate the computational performance and scalability of MCMAS+ using very large case studies. The obtained results strongly confirm the theoretical findings and make MCMAS+ practical. We finally compare our approach to other available approaches and show that it outperforms such approaches in terms of execution time, memory usage and number of considered intelligent agents

Model Checking Real-Time Conditional Commitment Logic using Transformation

A new logical language for real-time conditional commitments called RTCTLcc has been developed by extending the CTL logic with interval bounded until modalities, conditional commitment modalities, and fulfillment modalities. RTCTLcc allows us to express qualitative and quantitative commitment requirements in a convenient way. These requirements can be used to model multi-agent systems (MASs) employed in environments that react properly and timely to events occurring at time instants or within time intervals. However, the timing requirements and behaviors of MASs need an appropriate way to scale and bundle and should be carefully analyzed to ensure their correctness, especially when agents are autonomous. In this paper, we develop transformation algorithms that are fully implemented in a new Java toolkit for automatically transforming the problem of model checking RTCTLcc into the problem of model checking RTCTL (real-time CTL). The toolkit engine is built on top of the NuSMV tool, effectively used to automatically verify and analyze the correctness of real-time distributed systems. We analyzed the time and space computational complexity of the RTCTLcc model checking problem. We proved the soundness and completeness of the transformation technique and experimentally evaluated the validity of the toolkit using a set of business scenarios. Moreover, we added a capability in the toolkit to automatically scale MASs and to bundle requirements in a parametric form. We experimentally evaluated the scalability aspect of our approach using the standard ordering protocol. We further validated the approach using an industrial case study

Reducing model checking commitments for agent communication to model checking ARCTL and GCTL*

Social commitments have been extensively and effectively used to represent and model business contracts among autonomous agents having competing objectives in a variety of areas (e.g., modeling business processes and commitment-based protocols). However, the formal verification of social commitments and their fulfillment is still an active research topic. This paper presents CTLC+ that modifies CTLC, a temporal logic of commitments for agent communication that extends computation tree logic (CTL) logic to allow reasoning about communicating commitments and their fulfillment. The verification technique is based on reducing the problem of model checking CTLC+ into the problem of model checking ARCTL (the combination of CTL with action formulae) and the problem of model checking GCTL* (a generalized version of CTL* with action formulae) in order to respectively use the extended NuSMV symbolic model checker and the CWB-NC automata-based model checker as a benchmark. We also prove that the reduction techniques are sound and the complexity of model checking CTLC+ for concurrent programs with respect to the size of the components of these programs and the length of the formula is PSPACE-complete. This matches the complexity of model checking CTL for concurrent programs as shown by Kupferman et al. We finally provide two case studies taken from business domain along with their respective implementations and experimental results to illustrate the effectiveness and efficiency of the proposed technique. The first one is about the NetBill protocol and the second one considers the Contract Net protocol

Laparoscopy in management of appendicitis in high-, middle-, and low-income countries: a multicenter, prospective, cohort study.

BACKGROUND: Appendicitis is the most common abdominal surgical emergency worldwide. Differences between high- and low-income settings in the availability of laparoscopic appendectomy, alternative management choices, and outcomes are poorly described. The aim was to identify variation in surgical management and outcomes of appendicitis within low-, middle-, and high-Human Development Index (HDI) countries worldwide. METHODS: This is a multicenter, international prospective cohort study. Consecutive sampling of patients undergoing emergency appendectomy over 6 months was conducted. Follow-up lasted 30 days. RESULTS: 4546 patients from 52 countries underwent appendectomy (2499 high-, 1540 middle-, and 507 low-HDI groups). Surgical site infection (SSI) rates were higher in low-HDI (OR 2.57, 95% CI 1.33-4.99, p = 0.005) but not middle-HDI countries (OR 1.38, 95% CI 0.76-2.52, p = 0.291), compared with high-HDI countries after adjustment. A laparoscopic approach was common in high-HDI countries (1693/2499, 67.7%), but infrequent in low-HDI (41/507, 8.1%) and middle-HDI (132/1540, 8.6%) groups. After accounting for case-mix, laparoscopy was still associated with fewer overall complications (OR 0.55, 95% CI 0.42-0.71, p < 0.001) and SSIs (OR 0.22, 95% CI 0.14-0.33, p < 0.001). In propensity-score matched groups within low-/middle-HDI countries, laparoscopy was still associated with fewer overall complications (OR 0.23 95% CI 0.11-0.44) and SSI (OR 0.21 95% CI 0.09-0.45). CONCLUSION: A laparoscopic approach is associated with better outcomes and availability appears to differ by country HDI. Despite the profound clinical, operational, and financial barriers to its widespread introduction, laparoscopy could significantly improve outcomes for patients in low-resource environments. TRIAL REGISTRATION: NCT02179112

Global economic burden of unmet surgical need for appendicitis

Background: There is a substantial gap in provision of adequate surgical care in many low-and middle-income countries. This study aimed to identify the economic burden of unmet surgical need for the common condition of appendicitis. Methods: Data on the incidence of appendicitis from 170 countries and two different approaches were used to estimate numbers of patients who do not receive surgery: as a fixed proportion of the total unmet surgical need per country (approach 1); and based on country income status (approach 2). Indirect costs with current levels of access and local quality, and those if quality were at the standards of high-income countries, were estimated. A human capital approach was applied, focusing on the economic burden resulting from premature death and absenteeism. Results: Excess mortality was 4185 per 100 000 cases of appendicitis using approach 1 and 3448 per 100 000 using approach 2. The economic burden of continuing current levels of access and local quality was US $92 492 million using approach 1 and$73 141 million using approach 2. The economic burden of not providing surgical care to the standards of high-income countries was $95 004 million using approach 1 and$75 666 million using approach 2. The largest share of these costs resulted from premature death (97.7 per cent) and lack of access (97.0 per cent) in contrast to lack of quality. Conclusion: For a comparatively non-complex emergency condition such as appendicitis, increasing access to care should be prioritized. Although improving quality of care should not be neglected, increasing provision of care at current standards could reduce societal costs substantially

Pooled analysis of WHO Surgical Safety Checklist use and mortality after emergency laparotomy

Background The World Health Organization (WHO) Surgical Safety Checklist has fostered safe practice for 10 years, yet its place in emergency surgery has not been assessed on a global scale. The aim of this study was to evaluate reported checklist use in emergency settings and examine the relationship with perioperative mortality in patients who had emergency laparotomy. Methods In two multinational cohort studies, adults undergoing emergency laparotomy were compared with those having elective gastrointestinal surgery. Relationships between reported checklist use and mortality were determined using multivariable logistic regression and bootstrapped simulation. Results Of 12 296 patients included from 76 countries, 4843 underwent emergency laparotomy. After adjusting for patient and disease factors, checklist use before emergency laparotomy was more common in countries with a high Human Development Index (HDI) (2455 of 2741, 89.6 per cent) compared with that in countries with a middle (753 of 1242, 60.6 per cent; odds ratio (OR) 0.17, 95 per cent c.i. 0.14 to 0.21, P <0001) or low (363 of 860, 422 per cent; OR 008, 007 to 010, P <0.001) HDI. Checklist use was less common in elective surgery than for emergency laparotomy in high-HDI countries (risk difference -94 (95 per cent c.i. -11.9 to -6.9) per cent; P <0001), but the relationship was reversed in low-HDI countries (+121 (+7.0 to +173) per cent; P <0001). In multivariable models, checklist use was associated with a lower 30-day perioperative mortality (OR 0.60, 0.50 to 073; P <0.001). The greatest absolute benefit was seen for emergency surgery in low- and middle-HDI countries. Conclusion Checklist use in emergency laparotomy was associated with a significantly lower perioperative mortality rate. Checklist use in low-HDI countries was half that in high-HDI countries.Peer reviewe

Mortality of emergency abdominal surgery in high-, middle- and low-income countries

Background: Surgical mortality data are collected routinely in high-income countries, yet virtually no low- or middle-income countries have outcome surveillance in place. The aim was prospectively to collect worldwide mortality data following emergency abdominal surgery, comparing findings across countries with a low, middle or high Human Development Index (HDI). Methods: This was a prospective, multicentre, cohort study. Self-selected hospitals performing emergency surgery submitted prespecified data for consecutive patients from at least one 2-week interval during July to December 2014. Postoperative mortality was analysed by hierarchical multivariable logistic regression. Results: Data were obtained for 10 745 patients from 357 centres in 58 countries; 6538 were from high-, 2889 from middle- and 1318 from low-HDI settings. The overall mortality rate was 1⋅6 per cent at 24 h (high 1⋅1 per cent, middle 1⋅9 per cent, low 3⋅4 per cent; P < 0⋅001), increasing to 5⋅4 per cent by 30 days (high 4⋅5 per cent, middle 6⋅0 per cent, low 8⋅6 per cent; P < 0⋅001). Of the 578 patients who died, 404 (69⋅9 per cent) did so between 24 h and 30 days following surgery (high 74⋅2 per cent, middle 68⋅8 per cent, low 60⋅5 per cent). After adjustment, 30-day mortality remained higher in middle-income (odds ratio (OR) 2⋅78, 95 per cent c.i. 1⋅84 to 4⋅20) and low-income (OR 2⋅97, 1⋅84 to 4⋅81) countries. Surgical safety checklist use was less frequent in low- and middle-income countries, but when used was associated with reduced mortality at 30 days. Conclusion: Mortality is three times higher in low- compared with high-HDI countries even when adjusted for prognostic factors. Patient safety factors may have an important role. Registration number: NCT02179112 (http://www.clinicaltrials.gov)

Global variation in anastomosis and end colostomy formation following left-sided colorectal resection

Background End colostomy rates following colorectal resection vary across institutions in high-income settings, being influenced by patient, disease, surgeon and system factors. This study aimed to assess global variation in end colostomy rates after left-sided colorectal resection. Methods This study comprised an analysis of GlobalSurg-1 and -2 international, prospective, observational cohort studies (2014, 2016), including consecutive adult patients undergoing elective or emergency left-sided colorectal resection within discrete 2-week windows. Countries were grouped into high-, middle- and low-income tertiles according to the United Nations Human Development Index (HDI). Factors associated with colostomy formation versus primary anastomosis were explored using a multilevel, multivariable logistic regression model. Results In total, 1635 patients from 242 hospitals in 57 countries undergoing left-sided colorectal resection were included: 113 (6·9 per cent) from low-HDI, 254 (15·5 per cent) from middle-HDI and 1268 (77·6 per cent) from high-HDI countries. There was a higher proportion of patients with perforated disease (57·5, 40·9 and 35·4 per cent; P < 0·001) and subsequent use of end colostomy (52·2, 24·8 and 18·9 per cent; P < 0·001) in low- compared with middle- and high-HDI settings. The association with colostomy use in low-HDI settings persisted (odds ratio (OR) 3·20, 95 per cent c.i. 1·35 to 7·57; P = 0·008) after risk adjustment for malignant disease (OR 2·34, 1·65 to 3·32; P < 0·001), emergency surgery (OR 4·08, 2·73 to 6·10; P < 0·001), time to operation at least 48 h (OR 1·99, 1·28 to 3·09; P = 0·002) and disease perforation (OR 4·00, 2·81 to 5·69; P < 0·001). Conclusion Global differences existed in the proportion of patients receiving end stomas after left-sided colorectal resection based on income, which went beyond case mix alone

Representing and Reasoning about Communicative Conditional Commitments

ABSTRACT Social commitments provide a powerful representation for modeling multi-agent interactions without relinquishing part of agents autonomy and flexibility. However, distinguishing between different but related types of conditional commitments, a natural frame of social commitments, is not considered yet. In this paper, we define a new logical language, CTL cc , which extends CTL with modalities to represent conditional commitments and their fulfillments using the formalism of interpreted systems. Such a language excludes the paradox that plagues the semantics of fulfilling commitments in the literature. We present a set of rules to reason about conditional commitments and their fulfillments. (resp. τi : Li × Acti → Li), where ACT = Act1 × . . . × Actn and each component a ∈ ACT is a &quot;joint action&quot; Categories and Subject Descriptors The idea is that a communication channel between i and j does exist iff V ari ∩V arj̸ = ∅. means the values of x in li(g) for i and in lj(g ′ ) for j are the same. As commitments are established through communication among agents, we call them communicative conditional commitments. Definition 1. A model of communicative conditional commitments generated from interpreted systems is a tupl