Web service is a standard for publishing services for users to access. Currently, more and more services are provided on various web sites. Notably, users access web services based on their preferences. An autonomous mechanism for dynamic and intelligent access to such personalized web services is thus a necessity. Using agent and ontology technologies seem to provide this much-needed capability. Unfortunately, there seems to lack either enough knowledge representation to operational concepts of agent or the engines to use the knowledge. This book presents a novel group-based agent architecture, in which the operational ontologies and engines are proposed to generate semantic behavior to solve the problem above. Combining it with user ontology, preferred value of services can be evaluated dynamically by agent to access personalized web service. We further extend the 22 FIPA communicative acts to propose 13 group communicative acts and 3 associated interactive protocols in order to facilitate the communication among group-based agents. We figure that this architecture can easily extend the engines and the ontologies to generate semantic behaviors to meet user preferences.