Abstract

Abstract

The recent advances in microelectro devices have led the researchers to an area of developing a large distributed system that consist of small, wireless sensor nodes. These sensor nodes are usually equipped with sensors to perceive the environment. Synchronization is an important component of almost all distributed systems and has been studied by many researchers. There are many solutions for the classical networks, but the traditional synchronization techniques are not suitable for sensor networks because they do not consider the partitioning of the network and message delay. Additionally, limited power, computational capacity, and memory of the sensor nodes make the problem more challenging for wireless sensor networks. This paper examines the clock synchronization issues in wireless sensor networks. Energy efficiency, cost, scalability, lifetime, robustness, and precision are the main problems to be considered in design of a synchronization algorithm. There is no one single system that satisfies all these together. A comparison of different clock synchronization algorithms in wireless sensor networks with a main focus on energy efficiency, scalability, and precision properties of them will be provided here.

Abstract-Email has become one of the fastest and most economical forms of communication. However, the increase of email users has resulted in the dramatic increase of spam emails during the past few years. As spammers always try to find a way to evade existing filters, new filters need to be developed to catch spam. Ontologies allow for machine-understandable semantics of data. It is important to share information with each other for more effective spam filtering. Thus, it is necessary to build ontology and a framework for efficient email filtering. Using ontology that is specially designed to filter spam, bunch of unsolicited bulk email could be filtered out on the system. Similar to other filters, the ontology evolves with the user requests. Hence the ontology would be customized for the user. This paper proposes to find an efficient spam email filtering method using adaptive ontology

Ontologies play a key role in realizing the full power of e-technology. Ontologies allow for machine-understandable semantics of data, and facilitate the search, exchange, and integration of knowledge for B2B (business-to-business) and B2C (business-to-consumer) e-commerce. Ontology is defined as the specification of shared knowledge (Waterson & Preece, 1999). By using semantic data, the usability of e-technology can be facilitated. There are several languages like XML (extensible markup language), RDF (resource description framework), RDFS (RDF schema), DAML+OIL (DARPA Markup Language+Web Ontology Language), and OWL. Many tools have been developed for implementing metadata of ontologies using these languages. However, current tools have problems with interoperation and collaboration. The primary goal of this survey is to introduce and understand several tools through their use. Therefore, we can develop a new generation of tools that not only support more capabilities, but also solve the problems of current tools.