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Tool for Entity Relationship Diagrams (TERD).
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This tool is intended for entity relationship diagrams (ERDs) that are
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used in classic Entity Relationship (ER) modeling.
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More about the drawing of ERDs can be found in chapter 4 of the
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user's guide and more about the use of this notation technique can be
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found in appendix A of the user's guide.
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Diagram editing in general.
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Diagrams that are made by a diagram editor are a special
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kind of graph consisting of nodes and edges and with a certain
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representation. In the representation of a graph, nodes and edges are
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shown as shapes (boxes, lines, diamonds etc.).
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Documents should satisfy certain constraints. Most constraints
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are specific for the particular diagram technique supported by the
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editor. In the editors there are three kinds of constraints:
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1. Built-in constraints which are constraints which can never be
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violated because there is no command in the user interface to achieve
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2. Immediately enforced constraints: when you perform a command that
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would violate a constraint that is immediately enforced, this command
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is rejected immediately by the editor and a pop-up window with an error
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3. Soft constraints which are constraints that can be violated.
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Soft constraints are checked by the editor when the Check Document
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from the Document menu is issued by you. Check Document displays a list
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of error messages in a pop-up window. As opposed to the previous two
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classes of constraints, you are responsible for correcting the diagram.
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lib/help/TERDIntro
