Rectangles represent objects, diamonds represent a certain association between two objects, and triangles represent a further subdivision of a certain object. Example: A research director is like a normal researcher (does research also), with the added functionality that it has to supervise a section.
The diagram is read right to left, top to bottom.
The dashed line indicates that this is an external relationship; assistants are in fact not part of the RD.
If you need clarifications, ask.
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