Nested Petri nets (NP-nets) have proved to be one of the convenient formalisms for distributed multi-agent systems modeling and analysis. It allows representing multi-agent systems structure in a natural way, since tokens in the system net are Petri nets themselves, and have their own behavior. Multi-agent systems are highly concurrent. Verification of such systems with model checking method causes serious difficulties arising from the huge growth of the number of system intermediate states (state-space explosion problem). To solve this problem an approach based on unfolding system behavior was proposed in the literature. Earlier in  the applicability of unfolding for nested Petri nets verification was studied, and the method for constructing unfolding for safe conservative nested Petri nets was proposed. In this work we propose another method for constructing safe conservative nested Petri nets unfoldings, which is based on translation of such nets into classical Petri nets and applying standard method for unfolding construction to them. We discuss also the comparative merits of the two approaches.
Graph partitioning is required for solving tasks on graphs that need to be split across disks or computers. This problem is well studied, but most results are not suitable for processing graphs with billons of nodes on commodity clusters, since they require shared memory or low-latency messaging. One approach suitable for cluster computing is Balanced Label Propagation, based on distributed label propagation algorithm for community detection. In this work we show how multi-level optimization can be used to improve partitioning quality of Balanced Label Propagation. One of major difficulties with distributed multi-level optimization is finding a matching in the graph. The matching is needed to choose pairs of vertices for collapsing in order to produce a smaller graph. As this work shows, simply splitting graph into several parts and finding matching in these parts independently is enough to improve the quality of partitioning generated by Balanced Label Propagation. Proposed algorithm can be implemented within any framework that supports MapReduce. In our experiments, when graphs were partitioned into 32 parts, ratio of edges that don’t cross partitions increased from 54-60% to 66-70%. One of significant problems of our implementation is performance – work time of multi-level algorithm was approximately twice that of the original algorithm. It seems likely that implementation can be improved so that multi-level algorithm would achieve better computational performance as well as partitioning quality.
In October 2013, the eighth meeting of researchers in the field of databases was held. The first such meeting took place in February 1988, so that 25 years passed between them. After each meeting, a report was published containing an overview of the current state of the field and a research program for the nearest future, a kind of set of forecasts for the development of research activities. This paper looks at the most interesting forecasts from the reports of the research meetings, discusses how they proved to be valid, to what extent they were true or not. Among the various problems of database technology under consideration are the following: the role of specialized hardware in building effective DBMS; SQL and database applications; perspectives of object-relational extensions; distributed heterogeneous database systems; databases and Web; databases and data warehouses, OLAP and data mining; component organization of DBMS; query optimization criteria; self-tuning and self-management of DBMS; DBMS architecture and new hardware capabilities: SSD, non-volatile memory, massively multithreaded processors; specialized DBMS; data fusion and data spaces; the Big Data problem and the response to it in the database community; architectural shifts in computing.
Requirements are an integral part of any software and hardware development process. The area where requirements become significantly important is the development of safety-critical systems which usage may cause risks on human lives. So the process of their development is often maintained by certification centers that requires from developers to meet the best practices supporting the safety of end product. This article reveals one possible approach to requirements management that was based on experience of embedded hardware development for civil avionics. This approach is now spread over different areas. Authors list the set of common tasks related to given approach. They also define the set of software features used to reduce the complexity of development and to mitigate risks. Authors review set of existing solutions in requirements management area using the listed features. In this article it is also defined on how given features can be applied within the given approach.