WebIME is an Web-based integrated modeling environment that implements a multi-facetted modeling approach to mathematical model representation and management. Key features of WebIME include the follwing: (ⅰ) sharing of modeling knowledge on the Web, (ⅱ) a user-friendly interface for creating, maintaining, and solving models, (ⅲ) independent management of mathematical models from conceptual models, (ⅳ) object-oriented conceptual blackboard concept, (ⅴ) multi-facetted mathematical modeling, and (ⅵ) declarative representation of mathematical knowledge. This paper presents details of design and implementation issues that were encountered in the development of WebIME.