Objective: The student is able to use object diagrams to communicate ideas in familiar domains. Initial script for introducing object diagrams:
Here we have an object diagram that represents a situation in some particular school. The actual school is much larger; we are only representing a subset of all the situations, and there are many more types of links and many more types of objects that might be used. An object diagram can be paraphrased in a natural language. Here is a description that can be deducted from the above object diagram. Based on general background knowledge, a few details have been added parenthetically, but these are not explicitly represented in the diagram. The instructor of the Geometry I course meeting at 13:00 is Professor Diethelm. That course has three students waiting for some reason (perhaps to be added to the course if a seat becomes available). The first student waiting is Harrold Bolz, the second is John Jones, and the third is Sally Smith. (Perhaps they are ordered by priority to be admitted into the course, like a waiting line.) John Jones and Sally Smith both have Professor Buck as their advisor. Sally can also consult with Professor Diethelm as her advisor. Because the links are not ordered, we cannot tell if she has a preference for one over the other. Harold Bolz has Professor Buck as his sole advisor. Facts about object diagrams Objects are drawn as rectangles with two compartments. The top compartment has an identifier followed by a colon and then the type of object that is represented, underlined. For instance:
Notice that the identifier gives no indication of what the object represents. It is just made up so we can refer to the object without pointing to it on the diagram. In this particular diagram, we can also refer to students by their name, since each one has a name that’s unique. In this case, it is perfectly okay to omit the object’s identifier, but you must still precede the object’s type with a colon, so...
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