Thomas is a systems analyst for Top Flight Systems Consulting Co., Inc. Thomas has been with Top Flight Systems for three years and has so far worked primarily as a programmer on several large implementation engagements. At long last, Thomas has been assigned to a project team as a systems analyst, and he has worked hard to apply the concepts he learned in college to his work.

Thomas’ manager, Jeff, is a hard-driving perfectionist who has Thomas more than a little intimidated. Jeff’s demanding standards and blunt criticisms did a lot to motivate Thomas to do well on the development of the process model for their current project. Thomas spent long hours carefully balancing the data flow diagrams, making sure that the terminology was consistent, and decomposing the diagrams down to the same level of detail. Thomas was relieved when Jeff’s review of his work resulted in only a few minor changes to the models.

Now it’s time to begin development of the system’s data model, and Thomas is more nervous about this task. Data modeling was never his strength in college. It always seemed so mysterious. Thomas began his first draft of the data model by going through the process model descriptions and identifying data entities and attributes that seemed important to the business system. He then sketched in some relationships between entities, and tried to determine the relationships’ cardinality and modality. He always got confused about those two concepts. He knew he’d need to review some of his college textbooks at home tonight to try and make sure he’d done things right.

Suddenly, Jeff appeared at his desk and snatched up the ERDs he’d just drafted. After glancing through them, Jeff threw them down on Thomas’ desk with disgust. “Thomas,” said Jeff, “is this the best you can do? In just two minutes I can see at least three relationships where you’ve messed up the cardinality and modality. Plus, I’ve never seen such a bunch of Many-to-Many relationships on one diagram. Haven’t you ever heard of an intersection entity? This kind of work won’t cut it here at Top Flight, Thomas. I expect to see a data model that makes sense tomorrow!” As Jeff turned on his heel and walked away, Thomas felt about two inches tall.

Help Thomas out. Prepare a concise review of cardinality and modality that will help him understand the concepts and apply them correctly to his model. Also, develop an explanation of intersection entities and how they can be used to remove many-to-many relationships from a data model.