Tackling Universal Properties of Minimal Trap Spaces of Boolean Networks

Minimal trap spaces (MTSs) capture subspaces in which the Boolean dynamics is trapped, whatever the update mode. They correspond to the attractors of the most permissive mode. Due to their versatility, the computation of MTSs has recently gained traction, essentially by focusing on their enumeration. In this paper, we address the logical reasoning on universal properties of MTSs in the scope of two problems: the reprogramming of Boolean networks for identifying the permanent freeze of Boolean variables that enforce a given property on all the MTSs, and the synthesis of Boolean networks from universal properties on their MTSs. Both problems reduce to solving the satisfiability of quantified propositional logic formula with 3 levels of quantifiers ($\exists\forall\exists$). In this paper, we introduce a Counter-Example Guided Refinement Abstraction (CEGAR) to efficiently solve these problems by coupling the resolution of two simpler formulas. We provide a prototype relying on Answer-Set Programming for each formula and show its tractability on a wide range of Boolean models of biological networks.Comment: Accepted at 21st International Conference on Computational Methods in Systems Biology (CMSB 2023

The role of community conversations in facilitating local HIV competence: case study from rural Zimbabwe

Background This paper examines the potential for community conversations to strengthen positive responses to HIV in resource-poor environments. Community conversations are an intervention method through which local people work with a facilitator to collectively identify local strengths and challenges and brainstorm potential strategies for solving local problems. Methods We conducted 18 community conversations (with six groups at three points in time) with a total of 77 participants in rural Zimbabwe (20% HIV positive). Participants were invited to reflect on how they were responding to the challenges of HIV, both as individuals and in community groups, and to think of ways to better support openness about HIV, kindness towards people living with HIV and greater community uptake of HIV prevention and treatment. Results Community conversations contributed to local HIV competence through (1) enabling participants to brainstorm concrete action plans for responding to HIV, (2) providing a forum to develop a sense of common purpose in relation to implementing these, (3) encouraging and challenging participants to overcome fear, denial and passivity, (4) providing an opportunity for participants to move from seeing themselves as passive recipients of information to active problem solvers, and (5) reducing silence and stigma surrounding HIV. Conclusions Our discussion cautions that community conversations, while holding great potential to help communities recognize their potential strengths and capacities for responding more effectively to HIV, are not a magic bullet. Poverty, poor harvests and political instability frustrated and limited many participants’ efforts to put their plans into action. On the other hand, support from outside the community, in this case the increasing availability of antiretroviral treatment, played a vital role in enabling communities to challenge stigma and envision new, more positive, ways of responding to the epidemic

Digital Government Systems: Tackling The Legacy Problem Through A Game-Based Approach To Business Requirements Analysis

Government agency reliance on legacy systems is problematic: they are costly to maintain, difficult to integrate with and they hinder innovation. However, the replacement of legacy systems is not a straightforward endeavor, and it often results in technology substitution that is not accompanied by business process change. The focus of this dissertation is on the phenomenon of legacy system replication wherein the requirements for applications replacing outdated technologies mimic legacy features and reflect status quo operational processes that have been historically shaped by the legacy system itself. This problem is referred to throughout the dissertation as the “legacy problem.” The dissertation investigates its roots and proposes an approach to overcome it. Specifically, a mixed method research approach is taken, including a survey of public sector practitioners to explore the extent of the legacy problem, and a series of semi-structured interviews with government information technology and management professionals to delve into the dynamics of legacy system replacement projects. Findings indicate that the legacy problem often stems from a lack of critical analysis of business requirements and the desire to minimize the risks associated with organizational change, which often result in missed opportunities for digital government innovation. As a consequence, the dissertation proposes a candidate approach to deal with the legacy problem in the development of a requirements game (RE-PROVO) which supports requirements discussions structured around the themes of legacy (or heritage) preservation and innovation. The game is evaluated by local government practitioners through several iterations and their feedback is analysed to gauge the potential utility of the approach. The results indicate that with a streamlined user interface and accentuated game elements RE-PROVO can be a valuable and effective tool for requirements analysis in legacy system replacement projects

On protection in federated social computing systems

Nowadays, a user may belong to multiple social computing systems (SCSs) in order to benefit from a variety of services that each SCS may provide. To facilitate the sharing of contents across the system boundary, some SCSs provide a mechanism by which a user may “connect ” his accounts on two SCSs. The effect is that contents from one SCS can now be shared to another SCS. Although such a connection feature delivers clear usability advantages for users, it also generates a host of privacy challenges. A notable challenge is that the access control policy of the SCS from which the content originates may not be honoured by the SCS to which the content migrates, because the latter fails to faithfully replicate the protection model of the former. In this paper we formulate a protection model for a fed-eration of SCSs that support content sharing via account connection. A core feature of the model is that sharable con-tents are protected by access control policies that transcend system boundary — they are enforced even after contents are migrated from one SCS to another. To ensure faith-ful interpretation of access control policies, their evaluation involves querying the protection states of various SCSs, us-ing Secure Multiparty Computation (SMC). An important contribution of this work is that we carefully formulate the conditions under which policy evaluation using SMC does not lead to the leakage of information about the protection states of the SCSs. We also study the computational prob-lem of statically checking if an access control policy can be evaluated without information leakage. Lastly, we identify useful policy idioms

Secure Virtual Machine Migration in Cloud Data Centers

While elasticity represents a valuable asset in cloud computing environments, it may bring critical security issues. In the cloud, virtual machines (VMs) are dynamically and frequently migrated across data centers from one host to another. This frequent modification in the topology requires constant reconfiguration of security mechanisms particularly as we consider, in terms of firewalls, intrusion detection/prevention as well as IPsec policies. However, managing manually complex security rules is time-consuming and error-prone. Furthermore, scale and complexity of data centers are continually increasing, which makes it difficult to rely on the cloud provider administrators to update and validate the security mechanisms. In this thesis, we propose a security verification framework with a particular interest in the abovementioned security mechanisms to address the issue of security policy preservation in a highly dynamic context of cloud computing. This framework enables us to verify that the global security policy after the migration is consistently preserved with respect to the initial one. Thus, we propose a systematic procedure to verify security compliance of firewall policies, intrusion detection/prevention, and IPsec configurations after VM migration. First, we develop a process algebra called cloud calculus, which allows specifying network topology and security configurations. It also enables specifying the virtual machines migration along with their security policies. Then, the distributed firewall configurations in the involved data centers are defined according to the network topology expressed using cloud calculus. We show how our verification problem can be reduced to a constraint satisfaction problem that once solved allows reasoning about firewall traffic filtering preservation. Similarly, we present our approach to the verification of intrusion detection monitoring preservation as well as IPsec traffic protection preservation using constraint satisfaction problem. We derive a set of constraints that compare security configurations before and after migration. The obtained constraints are formulated as constraint satisfaction problems and then submitted to a SAT solver, namely Sugar, in order to verify security preservation properties and to pinpoint the configuration errors, if any, before the actual migration of the security context and the virtual machine. In addition, we present case studies for the given security mechanisms in order to show the applicability and usefulness of our framework, and demonstrate the scalability of our approach

The Daily Texan

Texas Student Medi