Table-Driven Detection and Resolution of Operation-Based Merge Conflicts with Mirador

This is the 1st International Workshop on Model Comparison in Practice, organized in the context of the 3rd International Conference on Model Transformation (ICMT 2010). For this year's workshop we have accepted 9 papers after detailed review and revision. The accepted papers reflect the state-of-the-art in research performed in the field of model comparison and address a wide range of issues including identification of corresponding model elements, model differencing, conflict detection and resolution, and model merging. More specifically, Koegel et. al. present operation-based conflict detection to detect conflicts in terms of model-changing operations, Westfechtel presents a formal approach for three-way merging of models in the context of the Eclipse Modelling Framework, Herrmannsdoerfer et. al. propose a generic operation recorder that simplifies the development of tool-support for operation-based model evolution approaches, Brosch et.al. introduce Colex, a collaborative web-based lexicon and invite the community to use it in order to build a body of knowledge in the area of conflict detection and resolution, Konemann proposes an approach for semantic grouping of model changes, Espinazo-Pagan et.al. propose a homogeneous repository for uniform management of metamodels and models in the development process, Protic et.al. present an approach for fine-grained metamodel-assisted comparison, Barrett et.al. introduce Mirador, a model merging tool that supports configurable model comparison strategies. Finally, Protic et.al. present a generic tool for visualization of model differences using polymetric views. The number of submitted and accepted papers indicates that the field of model comparison is an important and actively-researched field within the community. Our hope is that this workshop will trigger useful discussions and help with establishing a deeper understanding - and potentially new collaborations - between researchers. With this we wish you all an enjoyable and fruitful workshop.

Stochastic optimal control for aircraft conflict resolution under wind uncertainty

A method for conflict detection and resolution based on the parameterization of the aircraft intents is presented. The method is also based on the use of predefined trajectory patterns, which are in fact flight intents; these patterns include standard airline procedures and air traffic control regulations. The conflict resolution problem is formulated as a parametric optimization problem subject to constraints; the optimality criterium is defined so that the deviation from the intended (preferred) trajectories in the lateral profile is minimized. The resolution trajectory patterns take into account changes of the nominal waypoints (vectoring) and changes of the aircraft speeds. The method is applied to the case of multiple conflicts among commercial transport aircraft in converging traffic in the terminal area; different scenarios are considered, which include locked aircraft, that is, aircraft whose trajectories are known and fixed. The conflict detection and resolution algorithm relies on a kinetic trajectory predictor (nonlinear point-mass model with variable mass), which is accurate, flexible, and transparent, and provides the high-fidelity prediction required in the analysis of the demanding terminal area traffic. The cost of the global conflict resolution process is assessed, in terms of extra distance traveled, extra flight time, and extra fuel consumed for each aircraft.

With the rapid development of the aviation industry, the complexity and intertwinement of various aviation activities have been continuously increasing, leading to the escalating of potential conflicts in limited airspace resources. Efficient airspace management is crucial for flight safety. To address the issues of conflict detection and resolution in localized high-density multi-airspace environments, this paper proposes an end-to-end integrated framework that integrates octree spatial partitioning, hierarchical conflict detection, and a conflict resolution module based on the Improved Whale Migration Algorithm (IWMA). This framework takes the airspace safety separation standards as constraints and the minimization of multi-airspace adjustment offsets as the optimization objective. The IWMA integrates diverse population structures and multi-strategy optimization technologies to balance global search and local exploration capabilities and avoid falling into local optima. Experiments on high-density conflict scenarios of different scales have verified the effectiveness and robustness of the proposed method. Simulation results show that compared with traditional detection methods and other classic optimization algorithms, the conflict detection and resolution method proposed in this paper can quickly and efficiently provide reliable solutions for multi-airspace conflict issues.

The detection and resolution of conflicts among norms are key processes to guarantee the proper behavior of multi-agent systems (MAS) regulated by norms. A way of regulation is required to restrict and guide the autonomous and possibly heterogeneous software agents that act according to their own interests. When norms are applied to regulate MAS, normative conflicts may arise. A conflict between norms is a situation in which the fulfillment of a norm causes a violation of another one. We present and compare different techniques proposed to detect and resolve conflicts.

4D-trajectory based operations is one of the big enabler for future high-capacity, efficient and environmentally friendly air traffic management. Every aircraft is scheduled to fly along a predicted 4D path that can be calculated from gate to gate pre-flight. 4D trajectories are optimized individually for aircraft taking into account performance models, routes, weather conditions and airline preferences. However, individual calculation of trajectories does not ensure conflict-freeness with surrounding traffic. This work describes an efficient algorithm detecting conflicts for large traffic scenarios. Conflict detection is performed between aircraft trajectories, also taking into account environmental constraints like severe weather zones and restricted areas. Basic idea is an N-dimensional bisection of airspace allowing a significant reduction of complexity. Thus, potential conflicts are identified very fast. A slower high precision conflict check is performed on potential conflicts only. On average, conflicts of one 4D-trajectory can be detected in a European traffic sample holding more than 33 000 flights in less than 2.5 ms on standard PC hardware. Fast detection times are predestined for trial-and-error conflict resolution. Different conflict resolution methods are illustrated, taking into account the major key performance areas in air traffic management, e. g., safety, efficiency, and predictability. As an example, deconfliction is performed on an optimized version of aforementioned European traffic sample holding 33 000 flights.

Conflict Detection and Resolution (CD&R) for Unmanned Aerial Vehicles (UAVs) has become important consideration with remarkable development of sensor technology and autonomous control system. Since CD&R deals with safety of UAVs and aircraft, it has to be validated by rigorous analytical verification. This paper investigates the application of differential geometry to UAV CD&R algorithm for non-cooperating intruders such as static and dynamic obstacles. Two-dimensional geometry is used to detect a single conflict and multiple conflicts, and find the condition for resolution guidance. The existence and stability of the conflict resolution, which controls either heading angle only or heading angle and ground speed simultaneously, are then analysed. Whilst there exist region which the UAV can not resolve due to its physical and operational limitations as every CD&R algorithms, the resolution guidance can find the region and prove local stability using Lyapunov theory. The analysis and resolution guidance design do not rely on local linearisation and can be shown that the derived conflict resolution is equivalent concepts to Proportional Navigation Guidance (PNG) and Traffic alert and Collision Avoidance Systems (TCAS). The paper finishes with numerical simulation in two dimensions, illustrating the performance and properties of the proposed CD&R algorithm.

In this paper, we propose a conflict detection and resolution scheme of multi aircrafts for an intersection region of two aircraft flows. The scheme is based on dynamic flight models, which allows the status of aircrafts is checked constantly. Therefore, we can detect conflicts in real-time and determine the conflict resolution scheme based on optimal control theory and speed change. In order to demonstrate the validity of our scheme, two examples are designed: one is two aircrafts and the other is three aircrafts. These two examples show that the scheme is safe.

China has been gradually relaxing its ban on the use of low-altitude airspace across the country. To guarantee the high reliability of air traffic management (ATM), conflict detection and conflict resolution (CDR) approaches are indispensable to maintain safe separation between neighbouring small fixed-wing aircraft. In this study, we analyse a temporal and spatial integrated strategy for safety assessment purposes in opening the low-altitude urban airspace of Chinese pilot cities. First, we present a detailed mathematical description of the proposed algorithms based on a spatial grid partitioning system (SGPS). For our system, a conflict detection (CD) algorithm is designed to determine if two trajectories pass through the same grid space within overlapping time windows. A conflict resolution (CR) algorithm integrates a proposed time scheduling-based technique (TST) and vertical change-based technique (VCT), which operate under predetermined basic principles. Then, based on our novel CDR algorithms, a causal model is constructed in graphical modelling and analysis software (GMAS) to generate a state space that can provide a global perspective on scenario dynamics and better understanding of induced conflict occurrences. Finally, simulation results demonstrate that the proposed approach is practical and efficient.

Aiming at solving the conflict of military aircraft passing through airlines, after modeling and analyzing the scenario that aircraft flows fly to converge, a conflict detection and resolution approach is proposed. When the aircraft flow enters the pre-designated control zone, the conflict in the forward looking time is determined by a ‘sliding detection window’, which moves with the military aircraft. After analyzing resolution boundary condition, a conflict resolution model is established. In this way, the avoidance action, heading and speed change maneuvering, would not cause the domino effect. The analytical mathematics result has shown the viability.

Current investigations into urban aerial mobility, as well as the continuing growth of global air transportation, have renewed interest in Conflict Detection and Resolution (CD&R) methods. With the new applications of drones, and the implications of a profoundly different urban airspace, new demands are placed on such algorithms, further spurring new research. This paper presents a review of current CR methods for both manned and unmanned aviation. It presents a taxonomy that categorises algorithms in terms of their approach to avoidance planning, surveillance, control, trajectory propagation, predictability assumption, resolution manoeuvre, multi-actor conflict resolution, considered obstacle types, optimization, and method category. More than a hundred CR methods were considered, showing how most work on a tactical, distributed framework. To enable a reliable comparison between methods, this paper argues that an open and ideally common simulation platform, common test scenarios, and common metrics are required. This paper presents an overview of four CR algorithms, each representing a commonly used CR algorithm category. Both manned and unmanned scenarios were tested, through fast-time simulations on an open-source airspace simulation platform.

Reconciliation of replicated data objects is tedious and error-prone in eventually consistent systems. Syntactic reconciliation techniques use serializability or causality as the basis for conflict-detection and resolution. These techniques are fast and efficient and the resolutions can be directly managed at the database side. However, for use cases where conflict resolution demands knowledge of the application semantics, domain-specific semantic reconciliation is required. Semantic reconciliation techniques often involve maintaining all possible values and perform the resolution via domain-specific knowledge at the client side. This involves additional cost in terms of network bandwidth and latency, and considerable complexity. In this paper, we discuss the motivation and design of a novel data type called priority register that implements a domain-specific conflict detection and resolution scheme directly at the database side, while leaving open the option of additional reconciliation at the application level. Our approach uses the notion of an application-defined replacement ordering and we show that a data type parameterized by such an order can provide an efficient solution for applications that demand domain-specific conflict resolution. We also describe the proof-of-concept implementation of the priority register inside the Cassandra distributed storage system.

The Semantic Web is about collaboration and exchange of information. While the data on the Semantic Web is constantly evolving and meant to be collaboratively edited there is no practical transactional concept or method to control concurrent writes to a dataset and avoid conflicts. Thus, we follow the question, how can we ensure a controlled state of a SPARQL Store when performing non transactional write operations? Based on the Distributed Version Control System for RDF data implemented in the Quit Store we present the Quit Editor Interface Concurrency Control (QEICC). QEICC provides a protocol on top of the SPARQL 1.1 standard to identify, avoid, and resolve conflicts. The strategies reject, branch, and merge are presented to allow different levels of control over the conflict resolution. While the reject strategy gives full control to the client, with branch and merge it is even possible to postpone the conflict resolution and integrate it into the date engineering process.

As air traffic intensity increases and stochastic uncertainties, such as wind direction and speed, continue to impact air traffic controllers' workload significantly, airlines are increasingly pressured to reduce costs by flying via straighter/more direct trajectories. Due to these changes, it is important to search for new means/solutions for aircraft conflict resolution to ensure the required level of safety and rational flight trajectory. Such a solution could be the implementation of Dubin's method of flight trajectories. This paper aims to propose and deeply analyze a new mathematical model for two-aircraft conflict resolution where the Dubins method is applied in a dynamic conflict scenario. In this model, at a certain moment, the flight trajectory of one aircraft follows a path similar to a moving circle's tangential line. Upon that, the conflict detection and resolution (CDR) model considers wind uncertainty. The proposed CDR method could be applied when uncertainty such as wind direction and speed are inconstant (stochastic) throughout the simulation.

This paper is incidental to a research program of finding an automation system to govern the civil flight corridors in which the instrumentality of human agency is all but totally devolved onto a complex, multi-layered data electro-mathematical analyzer. Six major actualities comprising of dimensionality, probabilisticality, conflict detection, conflict resolution, maneuvering, global multiplicity of aircraft management, have become the focus of the proposed automation. The un-touched bench mark discourse of the prevalency of an “orderer-ordered” intercommunication between the aircraft agents and the Air Traffic Control meta-agent(s) has been kept sacrosanct for a variety of reasons to avert an over-revolutionary discourse change in a sphere of trafficking where any probable risk entails extraordinary losses of all sorts. A cutaneously rigid, layerized maths-speech act programming adapted by the present authors makes it feasible in the format of Prolog to deliver the responsibility of a mono-controller only capable of being in touch with just one flying object at each real-time instance on to some machine governing “more-than-several” aerospace SUSPENDING DOTS at the very same real-time instance.