Management of object-oriented action-based distributed programs

Phd ThesisThis thesis addresses the problem of managing the runtime behaviour of distributed programs. The thesis of this work is that management is fundamentally an information processing activity and that the object model, as applied to actionbased distributed systems and database systems, is an appropriate representation of the management information. In this approach, the basic concepts of classes, objects, relationships, and atomic transition systems are used to form object models of distributed programs. Distributed programs are collections of objects whose methods are structured using atomic actions, i.e., atomic transactions. Object models are formed of two submodels, each representing a fundamental aspect of a distributed program. The structural submodel represents a static perspective of the distributed program, and the control submodel represents a dynamic perspective of it. Structural models represent the program's objects, classes and their relationships. Control models represent the program's object states, events, guards and actions-a transition system. Resolution of queries on the distributed program's object model enable the management system to control certain activities of distributed programs. At a different level of abstraction, the distributed program can be seen as a reactive system where two subprograms interact: an application program and a management program; they interact only through sensors and actuators. Sensors are methods used to probe an object's state and actuators are methods used to change an object's state. The management program is capable to prod the application program into action by activating sensors and actuators available at the interface of the application program. Actions are determined by management policies that are encoded in the management program. This way of structuring the management system encourages a clear modularization of application and management distributed programs, allowing better separation of concerns. Managemental concerns can be dealt with by the management program, functional concerns can be assigned to the application program. The object-oriented action-based computational model adopted by the management system provides a natural framework for the implementation of faulttolerant distributed programs. Object orientation provides modularity and extensibility through object encapsulation. Atomic actions guarantee the consistency of the objects of the distributed program despite concurrency and failures. Replication of the distributed program provides increased fault-tolerance by guaranteeing the consistent progress of the computation, even though some of the replicated objects can fail. A prototype management system based on the management theory proposed above has been implemented atop Arjuna; an object-oriented programming system which provides a set of tools for constructing fault-tolerant distributed programs. The management system is composed of two subsystems: Stabilis, a management system for structural information, and Vigil, a management system for control information. Example applications have been implemented to illustrate the use of the management system and gather experimental evidence to give support to the thesis.CNPq (Consellho Nacional de Desenvolvimento Cientifico e Tecnol6gico, Brazil): BROADCAST (Basic Research On Advanced Distributed Computing: from Algorithms to SysTems)

Using a loadtime metaobject protocol to enforce access control policies upon user-level compiled code

This thesis evaluates the use of a loadtime metaobject protocol as a practical mechanism for enforcing access control policies upon applications distributed as user-level compiled code. Enforcing access control policies upon user-level compiled code is necessary because there are many situations where users are vulnerable to security breaches because they download and run potentially untrustworthy applications provided in the form of user-level compiled code. These applications might be distributed applications so access control for both local and distributed resources is required. Examples of potentially untrustworthy applications are Browser plug-ins, software patches, new applications, or Internet computing applications such as SETI@home. Even applications from trusted sources might be malicious or simply contain bugs that can be exploited by attackers so access control policies must be imposed to prevent the misuse of resources. Additionally, system administrators might wish to enforce access control policies upon these applications to ensure that users use them in accordance with local security requirements. Unfortunately, applications developed externally may not include the necessary enforcement code to allow the specification of organisation-specific access control policies. Operating system security mechanisms are too coarse-grained to enforce security policies on applications implemented as user-level code. Mechanisms that control access to both user-level and operating system-level resources are required for access control policies but operating system mechanisms only focus on controlling access to system-level objects. Conventional object-oriented software engineering can be used to use existing security architectures to enforce access control on user-level resources as well as system-resources. Common techniques are to insert enforcement within libraries or applications, use inheritance and proxies. However, these all provide a poor separation of concerns and cannot be used with compiled code. In-lined reference monitors provide a good separation of concerns and meet criteria for good security engineering. They use object code rewriting to control access to both userlevel and system-level objects by in-lining reference monitor code into user-level compiled code. However, their focus is upon replacing existing security architectures and current implementations do not address distributed access control policies. Another approach that does provide a good separation of concerns and allows reuse of existing security architectures are metaobject protocols. These allow constrained changes to be made to the semantics of code and therefore can be used to implement access control policies for both local and distributed resources. Loadtime metaobject protocols allow metaobject protocols to be used with compiled code because they rewrite base level classes and insert meta-level interceptions. However, these have not been demonstrated to meet requirements for good security engineering such as complete mediation. Also current implementations do not provide distributed access control. This thesis implements a loadtime metaobject protocol for the Java programming language. The design of the metaobject protocol specifically addresses separation of concerns, least privilege, complete mediation and economy of mechanism. The implementation of the metaobject protocol, called Kava, has been evaluated by implementing diverse security policies in two case studies involving third-party standalone and distributed applications. These case studies are used as the basis of inferences about general suitability of using loadtime reflection for enforcing access control policies upon user-level compiled code.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

10431 Abstracts Collection -- Software Engineering for Self-Adaptive Systems

From 24.10. to 29.10.2010, the Dagstuhl Seminar 10431 ``Software Engineering for Self-Adaptive Systems\u27\u27 was held in Schloss Dagstuhl~--~Leibniz Center for Informatics. During the seminar, several participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this paper. The first section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available

Graph Structures for Knowledge Representation and Reasoning

This open access book constitutes the thoroughly refereed post-conference proceedings of the 6th International Workshop on Graph Structures for Knowledge Representation and Reasoning, GKR 2020, held virtually in September 2020, associated with ECAI 2020, the 24th European Conference on Artificial Intelligence. The 7 revised full papers presented together with 2 invited contributions were reviewed and selected from 9 submissions. The contributions address various issues for knowledge representation and reasoning and the common graph-theoretic background, which allows to bridge the gap between the different communities

Run-time Variability with Roles

Adaptability is an intrinsic property of software systems that require adaptation to cope with dynamically changing environments. Achieving adaptability is challenging. Variability is a key solution as it enables a software system to change its behavior which corresponds to a specific need. The abstraction of variability is to manage variants, which are dynamic parts to be composed to the base system. Run-time variability realizes these variant compositions dynamically at run time to enable adaptation. Adaptation, relying on variants specified at build time, is called anticipated adaptation, which allows the system behavior to change with respect to a set of predefined execution environments. This implies the inability to solve practical problems in which the execution environment is not completely fixed and often unknown until run time. Enabling unanticipated adaptation, which allows variants to be dynamically added at run time, alleviates this inability, but it holds several implications yielding system instability such as inconsistency and run-time failures. Adaptation should be performed only when a system reaches a consistent state to avoid inconsistency. Inconsistency is an effect of adaptation happening when the system changes the state and behavior while a series of methods is still invoking. A software bug is another source of system instability. It often appears in a variant composition and is brought to the system during adaptation. The problem is even more critical for unanticipated adaptation as the system has no prior knowledge of the new variants. This dissertation aims to achieve anticipated and unanticipated adaptation. In achieving adaptation, the issues of inconsistency and software failures, which may happen as a consequence of run-time adaptation, are evidently addressed as well. Roles encapsulate dynamic behavior used to adapt players representing the base system, which is the rationale to select roles as the software system's variants. Based on the role concept, this dissertation presents three mechanisms to comprehensively address adaptation. First, a dynamic instance binding mechanism is proposed to loosely bind players and roles. Dynamic binding of roles enables anticipated and unanticipated adaptation. Second, an object-level tranquility mechanism is proposed to avoid inconsistency by allowing a player object to adapt only when its consistent state is reached. Last, a rollback recovery mechanism is proposed as a proactive mechanism to embrace and handle failures resulting from a defective composition of variants. A checkpoint of a system configuration is created before adaptation. If a specialized bug sensor detects a failure, the system rolls back to the most recent checkpoint. These mechanisms are integrated into a role-based runtime, called LyRT. LyRT was validated with three case studies to demonstrate the practical feasibility. This validation showed that LyRT is more advanced than the existing variability approaches with respect to adaptation due to its consistency control and failure handling. Besides, several benchmarks were set up to quantify the overhead of LyRT concerning the execution time of adaptation. The results revealed that the overhead introduced to achieve anticipated and unanticipated adaptation to be small enough for practical use in adaptive software systems. Thus, LyRT is suitable for adaptive software systems that frequently require the adaptation of large sets of objects

MetaBETA: Model and Implementation

Object-oriented programming languages are excellent for expressing abstractions in many application domains. The object-oriented programming methodology allows real-world concepts to modelled in an easy and direct fashion and it supports refinement of concepts. However, many object-oriented languages and their implementations fall short in two areas: dynamic extensibility and reflection.Dynamic extensibility is the ability to incorporate new classes into an application at runtime. Reflection makes it possible for a language to extend its own domain, e.g., to build type-orthogonal functionality. MetaBETA is an extension of the BETA language that supports dynamic extensibility and reflection. MetaBETA has a metalevel interface that provides access to the state of a running application and to the default implementation of language primities.This report presents the model behind MetaBETA. In particular, we discuss the execution model of a MetaBETA program and how type- orthogonal abstractions can be built. This includes precentation of dynamic slots, a mechanism that makes is possible ectend objects at runtime. The other main area covered in this report is the implementation of MetaBETA. The central component of the architecture is a runtime system, which is viewed as a virtual machine whose baselevel interface implements the functionality needed by the programming language