An appropriate approach for integrating UML-B allows us to map UML specifications into B specifications. Therefore, we can formally analyze an UML specification via the corresponding B formal specification. This point is significant because B support tools are available. We can also use UML specifications as a tool for building B specifications, so the development of B specifications become easier. Hence, an approach for a practical and rigorous software development, which is based on UML and B, from the requirements elicitation to the executable code, could be achieved. In this paper, we address the problem of automatic derivation of UML behavioral diagrams into B specifications, which has been so far an open issue. For this purpose, we propose a new approach for modeling class operations in B. Each class operation is mapped into a B operation. A class operation and its concerned data are mapped into the same B abstract machine (BAM). The calling-called dependency between class operations is used to arrange B operations of class operations into BAMs. For each calling-called pair of class operations, the B operation of the called operation participates in the implementation of the B operation of the calling operation.