Distributed Graphs and Graph Transformation

A distributed graph (N,D) consists of a network graph N and a commutative diagram D over the scheme N which associates local graphs D(ni) and graph morphisms D(e): D(n1) →D(n2) to nodes n1, n2 and edges e: n1 →n2 in N. Although there are several interesting applications of distributed graphs and transformations, even the basic pushout constructions for the double pushout approach of distributed graph transformation could be shown up to now only in very special cases. In this paper we show that the category of distributed graphs can be considered as a Grothendieck category over a specific indexed category, which assigns to each network N the category of all diagrams D of shape N. In this framework it is possible to give a free construction which allows to construct for each diagram D1 over N1 and network morphism h:N1 →N2 a free extension Fh(D1) over N2 and to show that the Grothendieck category is complete and cocomplete if the underlying category of local graphs has these properties. Moreover, an explicit construction for general pushouts of distributed graphs is given. This pushout construction is based on the free construction. The non-trivial proofs for free constructions and pushouts are the main contributions of this paper and they are compared with the special cases known up to now.

Qos-Driven Architectural Mining for Publish/Subscribe Systems Deployed on MANET

Analyzing huge amounts of log data is often a difficult task, especially if it has to be done in real time (e.g., fraud detection) or when large amounts of stored data are required for the analysis. Graphs are a data structure often used in log analysis. Examples are clique analysis and communities of interest (COI). However, little attention has been paid to large distributed graphs that allow a high throughput of updates with very low latency.In this paper, we present a distributed graph mining system that is able to process around 39 million log entries per second on a 50 node cluster while providing processing latencies below 10 ms. We validate our approach by presenting two example applications, namely telephony fraud detection and internet attack detection. A thorough evaluation proves the scalability and near real-time properties of our system.

Querying graph data often involves identifying matching paths, either as an end product, or as an intermediate step for further graph analysis. Distributed graph querying, suffers from high communication to computation costs, due to challenges in constructing comprehensive structural indexes. This could result in severe performance degradation in terms of turnaround time, which often worsens with increasing graph size and density. In this paper, we propose a novel topology abstraction layer, that helps improve query response time by reducing the communication overhead for selective exploration of large distributed graphs. We demonstrate the effectiveness of our model and also go on to show that our abstraction layer works well in both data-parallel and graph-parallel paradigms.

The issue of ontology evolution and change management is inadequately addressed by available tools and algorithms, mostly due to the lack of suitable knowledge representation formalisms to deal with temporal abstract notations and the overreliance on human factors. Also most of the current approaches have been focused on changes within the internal structure of ontologies and interactions with other existing ontologies have been widely neglected. In our research, after revealing and classifying some of the common alterations in a number of popular biomedical ontologies, we present a novel agent-based framework, Represent, Legitimate and Reproduce (RLR), to semi-automatically manage the evolution of bio-ontologies, with emphasis on the FungalWeb Ontology, with minimal human intervention. RLR assists and guides ontology engineers through the change management process in general and aids in tracking and representing the changes, particularly through the use of category theory and hierarchical graph transformation.

Smart grid solutions with enabling technologies such as energy management systems (EMS) and smart meters promote the vision of smart households, which also allows for active demand side in the residential sector. These technologies enable the control of residential consumption, local small-scale generation and energy storage systems to respond to time-varying prices. However, shifting loads simultaneously to lower price periods is likely to put extra stress on distribution system assets such as distribution transformers. Especially, additional new types of loads/appliances such as electric vehicles (EVs) can introduce even more burden on the operation of these assets, which is an issue that needs special attention. Such extra stress can cause accelerated ageing of distribution system assets and significantly affect the reliability of the system. In this study, the impact of a smart neighborhood load on distribution transformer ageing is investigated. The EMS of each household is designed to respond to prices and other signals emitted by the responsive load serving entity within the relevant demand response (DR) strategy. An optimization framework based on mixed-integer linear programming (MILP) is presented in order to define the EMS structure. Then, the equivalent ageing of the distribution transformer is examined with a thermal model under different scenarios. The case studies that are presented indicate that the integration of EVs in residential premises may indeed cause accelerated ageing of the distribution transformers, while the need to investigate the efficiency of dynamic pricing mechanisms is rendered evident.

The intelligence level of distribution networks keeps improving in recent years. For example, in China, the distribution transformer supervisory terminal unit(TTU), which can intelligently monitor and manage the distribution transformer area, is being widely installed in distribution networks. These TTUs can provide real-time distribution transformer operation data. To increase the value of these data, this paper focuses on the line switch statuses identification technology in distribution networks using TTU measurement data. Firstly, based on the analysis of the TTU measurement data, an optimization equation of which the objective function is the residual error between measurements and estimations is formulated. Secondly, the nonlinear terms in the original optimization equation are eliminated, and it is converted into a mixed integer quadratic programming(MIQP) problem so that it can be solved using the standard method. Moreover, a voltage measurement correction algorithm using the solution of the objective function is proposed. Finally, case studies are conducted to verify the effectiveness of the proposed method.

Graph Grammars are a visual formal language for which there are several techniques of system specification and verification. This fact makes them an attractive option for describing complex systems. Fuzzy graph grammars generalize the concept of graph grammars, using fuzzy graphs. A fuzzy graph is composed of vertices and edges that have an associated membership value, which varies within a range of 0 to 1. Due to the lack of technique and analysis tools for fuzzy graph grammars, their use is still quite limited. One way to allow the analysis of fuzzy graphs grammars is using the extension of existing graph grammar approaches, including the concept of membership in the graph components. There is a relational approach of graph grammars that allows the use of theorem provers to perform property analysis of systems described in this language. This approach is the basis of a translation of graph grammars into the Event-B language, which enables the use of theorem provers of the Rodin tool. Therefore, the aim of this work is to extend this graph grammar approach, including fuzzy concepts, to allow the use of the theorem proving technique to analyze fuzzy graph grammars. In order to set this extension was first necessary to define the notion of typed fuzzy graph grammars.

A graph-based approach to the compositional specification of distributed systems

The paper presents a conceptual framework for a module concept for graph transformation systems from a software engineering as well as from a theoretical point of view. The basic idea is to reuse concepts, which are known within or without the graph grammar field, to structure large specifications. These are the concept of distributed graph transformation systems, the concept of inheritance of specifications, and the import-export-interface concept. All these concepts are presented in a uniform framework based on the syntactical notion of a graph class specification and its semantics given by a graph transformation system. This is the basis for an explicit integration of these concepts and a corresponding specification language, to be discussed in a subsequent paper.

Firstly, net theory, which is a well established theory of distributed systems and processes [I] relies heavily on a graphical notation. One of the strengths of this theory is that many of the fundamental notions concerning concurrent systems and in particular, the dynamics of a concurrent systemcan be made transparent with the help of simple net diagrams and transformations of such diagrams. It is important to provide a solid formal foundation to this aspect of net theory and graph grammars appear to be the obvious tool for doing so. The second motivation is that in the study of concurrency problems that arise within the area of graph grammars [2] we think it is possible and fruitful to apply the concepts and techniques of net theory.

Distributed graph transformation has been used to specify static as well as dynamic aspects of distributed systems. To support distributed designs by different developers, local views are introduced. A local view on a distributed system consists of one local system, its import and export interfaces, and connected remote interfaces. The behavior of a local system is specified by a set of graph rules that are applicable only to the local view of the local system. Local systems communicate either synchronously or asynchronously via their import and export interfaces. Asynchronous communication is modeled by sequential application of graph rules, synchronous communication by the amalgamation of graph rules. We compose a distributed system grammar from the rule sets for local systems. The operational semantics of the distributed system is given by distributed transformation sequences.

High penetration level of rooftop small-scale renewable energy generation (REG) such as solar and wind power into the existing low voltage (LV) network would cause the flow of power in reverse direction. This would also vary the level of short-circuit current required for relays to operate. Relay settings would be required to properly detect the unpredictable fault current and isolate the faulty section. This paper investigates the impact of residential distributed generation (DG) penetration level on the typical UK low voltage network protection system. Studies were commenced to properly charge and discharge the home connected energy storage battery (ESB). ESB is used as a remedial measure to confine the flow of reverse power due to rooftop DGs. Penetration level DGs are modeled based on proper ESB charging and discharging states in daily load cycle. Short circuit analysis is simulated on Matlab/Simulink. The power flow from the transformer secondary is managed to avoid malfunctioning of relays according to daily load cycle. Short circuit analysis results are compared with the UK passive network to investigate the impact of the DG on the short circuit currents at distribution transformer.

Multi-stage optimization for energy management and trading for smart homes considering operational constraints of a distribution network

Improving the Usability of a Graph Transformation Language