Research On XML Real-time Data Compressing Method For PLC In Internet Of Things

With the development of Internet of Things, the number of perceived devices are increasing, the amount of they contained data is growing. XML has been widely used in the Internet of Things for its high flexibility advantages. XML data of perceived devices not only diverse, but also contain a lot of information redundancy, including XML's structure redundant information and related-time redundant information between real-time data of XML, these information redundancy occupy large amount of bandwidth in the Internet of Things. In fact, our network bandwidth is an upper limit, when the network bandwidth can't satisfy the amount of data transmission's meets in Internet of Things, it will hinder the development of the Internet of Things in the industry. To this end, people often use compression method to reduce the redundancy of XML data in Internet of Things.Firstly, this paper investigated the PLC remote monitoring project in Internet of Things, explained the importance of real-time XML data compression of PLC and analysis of the characteristics of existing compression methods. According to the characteristics of real-time data redundancy of Internet of things, analyzes the advantages and disadvantages of existing compression methods.Conventionally, there are two kinds of XML file compressor, one is universal, the other is XML dedicated. Dedicated compression can be done some optimization for structures in XML, so that its compression effect is better than universal one. But these compression method focus only compress a single document, they have not considered that XML data have time-related redundant information in the Internet of Things. Therefore, these compression methods are less effective for real-time data of XML in the Internet of Things.In this paper, we based existing XML dedicated compression method and combined real-time data redundancy features of XML in the Internet of Things, we propose a new compressing method for real-time data of XML, the new method is called XCiot(XML Document Compressing Method Based on Internet of Things). XCiot has two main levels of compression. The first level is mainly for the dictionary compression of real-time data of XML's time-related redundant information. The second level is mainly for the compression of the XML's structure redundancy.At last, we adopt the real-time data of XML of perceived PLC-equipment in the Internet of Things, and compare XCiot, XMill, XMLPPM, WinRAR, XWRT with each other based on the compressed test for the real-time data of XML. The test results show that XCiot have a higher compression ratio than other compression methods. The compression time of XCiot is slightly longer than some classical compression algorithms, these compression time are in the same order of magnitude. At the expense of little compression time, XCiot achieved higher compression result.