Presentation level integration now becomes an important and fast growing trend in enterprise computing and portal-based composite applications are the mainstream to realize it. Such applications use portlet and interactive web service, which usually offers several portlets, as their basic constituents. Hence, portlet description and discovery are the key issues that have to be considered. This paper proposes a novel concept POI (Presentation Oriented Interface) to describe the presentation features of a portlet, so that interactive web services may be extended to facilitate the selection and interoperation of portlets. Interactive web services discovery can be effectively achieved based on the calculation of POI similarity that considers both type and structure similarity. Experiments show that the proposed approach can improve the satisfaction of service discovery, thereby achieving better application integration at presentation level.