SECTION III Subject Area, Logical, and Physical Data Models Section III explores the three different levels of models: subject area, logical, and physical. You'll recall from the camera analogy that the format or film the camera uses is analogous to the three levels of modeling: subject area, logical, and physical. A subject area model (SAM) is analogous to a proof sheet that contains small thumbnail images of each photograph. It represents a business need. It is a very broad view, containing only the basic and critical concepts for a given scope. The logical data model (LDM) equates to the film negative; a perfect view of the picture, yet also impractical as you can't put a negative in a photo frame and show it to your friends. The LDM represents a detailed business solution, capturing the business requirements without complicating the model with implementation concerns such as software and hardware. The physical data model (PDM) equates to 93