The Web Services (WS) technology provides a comprehensive solution for representing, discovering and invoking services in a wide variety of environments, including SOA (Service Oriented Architectures) and grid computing systems. At the core of WS technology lie a number of XML-based standards, such as the Simple Object Access Protocol (SOAP), that have successfully ensured WS extensibility, transparency, and interoperability. Nonetheless, there is an increasing demand to enhance WS performance, which is severely impaired by XML's verbosity. SOAP communications produce considerable network traffic, making them unfit for distributed, loosely coupled and heterogeneous computing environments such as the open Internet. Also, they introduce higher latency and processing delays than other technologies, like Java RMI and CORBA. WS research has recently focused on SOAP performance enhancement.Many approaches build on the observation that SOAP message exchange usually involves highly similar messages (those created by the same implementation usually have the same structure, and those sent from a server to multiple clients tend to show similarities in structure and content). Similarity evaluation and differential encoding have thus emerged as SOAP performance enhancement techniques. The main idea is to identify the common parts of SOAP messages, to be processed only once, avoiding a large amount of overhead. Other approaches investigate non-traditional processor architectures, including micro-and macro-level parallel processing solutions, so as further increase the processing rates of SOAP/XML software toolkits.Thissurvey paper provides a concise, yet comprehensive review of the research efforts aimed at similarity-based SOAP performance enhancement. A unified view of the SOAP performance enhancement problem is provided, covering almost every phase of SOAP processing, ranging over message parsing, serialization, de-serialization, compression, multicasting, security evaluation, and data/instruction-level processing.
