Development and usage of online social networking web sites are growing rapidly. Millions members of these web sites publicly articulate mutual "friendship" relations and share user-created contents, such as photos, videos, files, and blogs. The advances in web designing technology and fast growing usage of online resources prompted web designers to improve features and architectures of social web sites. This paper, with the experience of the authors in developing the Iranian Experts Social Network containing above 120,000 official members, describes the features of Social Web Sites (SWSs) and proposes a taxonomy and comprehensive definition in designing such social networking tools. We then present different SWS architectures and also introduce some useful tools for social network analysis.