Investigating, Modeling, and Ranking Interface Complexity of Web Services on the World Wide Web

Analyzing factors of affecting Web Service invocation performance is a hot topic. Among the factors, service interface complexity is a key one investigated by much research work. However, these researches mainly analyze the impact on the performance of primitives, some simple data structures like mesh interface object, or array of them. For the complex data structures, these works lack of a systematic approach to characterize the impact. This paper firstly makes a detailed statistics of service interface complexity based on a large sample space (10K+ WSDL files) on the World Wide Web, and we find about 41.6% services contain complex data structures. The statistic results guide us to conduct many experiments for finding out the correlation of service interface complexity to invocation performance. We discover an interesting feature on commonly used Web Service platforms (Axis/gSOAP/.Net), called Data Structural Form Unaware. As each parameter or return value can be represented as a tree with two kinds of nodes, structure type node and primitive type node, then the feature means that the overhead caused by parameters or return values is independent of the organization of nodes in the trees, but it is only related with the number and the type of nodes. By this feature, we present a simple model to quantify the impact of service interface complexity. Using our model, a Service Interface Performance Vector can be calculated by parsing a WSDL file to estimate the overhead of service interface design. This vector, together with the invocation probability of each operation, generates the Service Interface Performance Score, a comprehensive complexity indicator which can be used to evaluate and rank the service interfaces. At last, a rank report of services on the WWW is shown. Our work can play a guiding role in service interface designing, service interface performance predicting, and ranking.