Nazir Ahmad Zafar

Formal Specification and Validation of a Localized Algorithm for Segregation of Critical/Noncritical Nodes in MAHSNs

Timely segregation of critical/noncritical nodes is extremely crucial in mobile ad hoc and sensor networks. Most of the existing segregation schemes are centralized and require maintaining network wide information, which may not be feasible in large-scale dynamic networks. Moreover, these schemes lack rigorous validation and entirely rely on simulations. We present a localized algorithm for segregation of critical/noncritical nodes (LASCNN) to the network connectivity. LASCNN establishes and maintains a k-hop connection list and marks a node as critical if its k-hop neighbours become disconnected without the node and noncritical otherwise. A noncritical node with more than one connection is marked as intermediate and leaf noncritical otherwise. We use both formal and nonformal techniques for verification and validation of functional and nonfunctional properties. First, we model MAHSN as a dynamic graph and transform LASCNN to equivalent formal specification using Z notation. After analysing and validating the specification through Z eves tool, we simulate LASCNN specification to quantitatively demonstrate its efficiency. Simulation experiments demonstrate that the performance of LASCNN is scalable and is quite competitive compared to centralized scheme with global information. The accuracy of LASCNN in determining critical nodes is 87% (1-hop) and 93% (2-hop) and of noncritical nodes the accuracy is 91% (1-hop) and 93% (2-hop).

Formal specification and validation of railway network components using Z notation

The railway interlocking system, being a safety-critical system, has achieved importance in the railway industry. Advanced technologies are being applied for its modelling, preventing collision and derailing of trains and at the same time allowing efficient movement of trains. In this study, we have applied Z notation by constructing a specification of the critical components of moving block interlocking. Graphs are used for modelling static components and are then integrated with Z to describe its entire state space. At first a real topology is transferred to a model topology in graph theory and then the critical components of the railway network, for example, tracks, switches, crossings and level crossing, are formalised. These components are integrated to define the static part of the system and then dynamic components, the state space of the static part, trains and controls, are integrated to describe the complete system. Formal specification of the system is given using Z and the model is analysed and validated using Z/EVES tool.

Requirements Analysis of Air Traffic Control System Using Formal Methods

Formal methods is an emerging technology that uses mathematical notations to write precise and unambiguous specifications which makes it possible to prove and analyze certain properties of the system so that errors and inconsistencies are identified during early stages of the development process. In this paper formal methods in terms of Z notation is applied for the specification of safety critical system of Air Traffic Control (ATC). Firstly, ATC system model in real world is described. For connectivity of different zones of airspace, the real world ATC system is transformed into a directed graph, which is then used to formalize the major components of formal ATC Model i.e static Topology, Network State, Aircraft and Controller. The whole Formal ATC Model is then presented as encapsulation of formal models of its basic components. Finally, the Formal A TC system Model is checked and analyzed with Z/EVES tool-set.

Formal analysis of departure procedure of air traffic control system

In recent years, the volume of air traffic has increased dramatically which caused for unwanted delay in flights at the airports during the departure and arrival process of aircrafts. In this paper we have proposed step by step modeling process for the departure of the aircraft with the coordination of the air traffic controllers. These controllers are responsible for safe and secure movement of the aircrafts. In this procedure initially the control of the aircraft is to the gate controller. Further after the operations of the gate controller the control is transfer to the ramp controller and the aircraft proceed for the departure in a series of the steps. The methodology used for this modeling process is VDM++ which is an object oriented model based formal approach. This method ensures the safety and correctness by identifying errors at early stages of systems designing. It also provides extremely valuable solution of problem and also improves the confidence of the quality of the software.

Designing Verifiable and Reusable Data Access Layer Using Formal Methods and Design Patterns

Layering is a concept widely used in computer and software modeling. Many modern information systems are designed and built using a layered model where the function of each layer is specified and well defined. In this paper we will be discussing the layer whose responsibilities include data extraction, manipulation and provision of data to the rest of the application. Common design problems that designers face while designing object oriented system can be resolved by using design patterns. These patterns are reusable solutions used heavily in application framework design. Formal methods are mathematical techniques used to construct models that can be proved for consistency, completeness and correctness of computerized systems. We have applied formal methods to data access layer patterns which has resulted a verifiable recipes for solving data access layer design problems. Our formal models are described using VDM++ specification language and are analyzed and validated using the VDM++ Toolbox.

Linking Finite Automata and Formal Methods Enhancing Modeling Power for Complex Systems

Automata have various applications and it plays an important role in computer science, particularly, in modeling behavior of systems. Z notation is an ideal one to be used defining state space of a system and then operations over it. Consequently, it requires an integration of automata and Z increasing its modeling power. Further, finite automata may have different implementations therefore if we give a mathematical analysis and describe formal specification of it before implementing then correctness of a model can be argued. Formal methods are rigorous mathematical techniques which can be used for specification of software systems. To achieve an objective of integration of approaches, we have combined automata and Z. Formalism of this relationship is analyzed and validated using Z/EVES tool.

Towards the formalization of railway interlocking system using Z-notations

Railway interlocking system is a safety critical system. Its malfunction can cause the loss of human life and severe injuries. To remove difficulties from this type of system better and advanced methodologies are required. This paper presents the use of Z-specification to specify the safety properties of the train system. The paper provides division of railway track into sectors and further division into segments. For the safety of the train a safe distance (open block) is associated with trains to avoid collision. Furthermore, this work uses the circular block around the crossing region. The circular block changes its state from green to red whenever it becomes occupied. Moreover the paper also specifies the safety of trains along the linear motion. This work uses the approach of promotion, which provides relation from local to global system. The authors take train as local system and relate it to the whole system through the operation of promotion. The paper also shows how formal methods are used to specify industrial application successfully.

Verifying Monoid and Group Morphisms over Strongly Connected Algebraic Automata

Automata theory has played an important role in theoretical computer science since last couple of decades. The alge-braic automaton has emerged with several modern applications, for example, optimization of programs, design of model checkers, development of theorem provers because of having certain interesting properties and structures from algebraic theory of mathematics. Design of a complex system requires functionality and also needs to model its control behavior. Z notation has proved to be an effective tool for describing state space of a system and then defining operations over it. Consequently, an integration of algebraic automata and Z will be a useful computer tool which can be used for modeling of complex systems. In this paper, we have linked algebraic automata and Z defining a relationship between fundamentals of these approaches which is refinement of our previous work. At first, we have described strongly connected algebraic automata. Then homomorphism and its variants over strongly connected automata are specified. Next, monoid endomorphisms and group automorphisms are formalized. Finally, equivalence of endomorphisms and automorphisms under certain assumptions are described. The specification is analyzed and validated using Z/Eves toolset.

Possible Improvements in UML Behavior Diagrams

Although, Unified Modeling Language (UML) has become a de-facto standard for design and specification of object oriented systems but its structures being semi-formal in nature have various disadvantages. The UML diagrams lack with defining semantics of the functionality of a system to be developed. Automata theory and formal methods are proved powerful at requirement specification, modeling, design and test case generation. To address and realize the benefits of liking UML, automata and formal methods, our project on formalization of UML diagrams is in progress. This paper is continuation of the same project in which behavior diagrams namely use case, activity and state diagrams are selected for critical analysis and possible improvements. Advantages, disadvantages and limitations of the diagrams are addressed. Finally, a treatment is suggested to link UML diagrams with nondeterministic and parallel finite automata to enhance modeling power of UML for facilitating the software development procedures.

Modeling Agent-Based Systems Using X-Machine and Z Notation

Developing correct and complete real-world software applications is a difficult task in terms of the number and flexibility of the essential components and their interrelationship. As the field of agent-based computing matures, the requirements of well-founded techniques and methodology for such systems modeling will increased. This paper used integration of two well known modeling techniques, X-machines and Z notation for modeling and writing the specification of agent-based systems. This modeling approach supports the behavioral modeling, data modeling and property analysis of agent-based systems. It also provides a mechanism for translating the formal model to executable code.