I just started learning about Databases, and my first assignment has information about an Art Museum that we are supposed to use to define a DB for, demonstrated with an EER Diagram.

One specification is as follows:

"The museum has a collection of ART_OBJECTS. Each ART_OBJECT has a unique Id_no, an Artist (if known), a Year (when it was created, if known), a Title, and a Description. The art objects are categorized in several ways, as discussed below."

What role, if any, does "if known" play in terms of the diagram? I reviewed the instructors notes looking for something resembling such specification, but I couldn't find anything in the diagram components that would imply whether or not information is available. Thoughts?

  • My guess is they want to either allow a null creation year (most likely for an assignment), or something like a range (most likely for real life IMO), ie "XYZ statute was created sometime between 1200 and 1100 BCE." That being said you should ask for clarification from your instructor. They're really the only person who can answer this. – Erik Feb 1 '17 at 20:37

In the logical model it means that the attribute is optional, which translates into a nullable column in the physical implementation.

  • ok, but does this translate to any specific notation in an EER Diagram of this field? – Natalie Spatharakis Feb 1 '17 at 18:46
  • Well, whatever notation you use for optional attributes. Your instructor should have provided a reference to the conventions he or she expects. May be you specify the attribute cardinality as (0,1), or draw it with the dotted line, or something. – mustaccio Feb 1 '17 at 18:47

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