Building a Data Warehouse requires focusing closely on understanding three main areas; the source area, the destination area, and the mapping area (ETL processes). The source area has standard models such as entity relationship diagram, and the destination area has standard models such as star schema, but the mapping area has no standard model till now. During the last few years, researchers and developers had proposed various attempts to put a standard conceptual design of ETL processes in data warehousing. These attempts try to represent the main mapping activities at the conceptual level. Due to the variation and limitations of the proposed trials, this work aims at presenting these conceptual modeling techniques, classify them into broad approaches, and show the features of each. In addition, we introduce a novel model proposed for conceptual designing of ETL processes in data warehouse systems. This model is built upon the enhancement of the previous trials by supporting some missing mapping features. A complete prototype tool is implemented to illustrate the feasibility of the new model.