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in the base case of the inductive definition of the operations of the relational algebra there is also the so called "constant relation" (as for example found in the definition here https://www2.cs.sfu.ca/CourseCentral/354/zaiane/material/notes/Chapter3/node9.html). However, until now I have not understood the following points:

  • what is it?
  • what is it good for?
  • what does it look like?
  • can one use it to create "customized" databases (i.e. that I can define them completely manually by inserting the elements that I want)?

Thanks for you help!

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  • $\begingroup$ Which 'inductive definition'? What is 'the so called "constant relation"'? What are '"customized" databases'? What is the context of your question & how is your question not answered there?Use enough words, sentences & references to parts of examples to clearly & fully say what you mean. How to Ask PS Putting words in scare quotes does not clarify the idiosyncratic meaning that you don't make clear by actually saying what you mean. $\endgroup$
    – philipxy
    Jun 2, 2021 at 19:44
  • $\begingroup$ I hope the edit satisfies your critique $\endgroup$
    – sorry
    Jun 2, 2021 at 20:03
  • $\begingroup$ Please put what is needed to ask your question in your post, not just at a link. Please use text, not images/links, for text. Paraphrase and/or quote from other text. Give just what you need & relate it to your problem. Give credit. Use block or inline quote format as appropriate. Use images only for what cannot be expressed as text or to augment text. Ask 1 (specific researched non-duplicate) question re where you are 1st stuck & explain about being stuck & what you do understand. help center $\endgroup$
    – philipxy
    Jun 2, 2021 at 20:07
  • $\begingroup$ That resource is poor. But: It does tell you, it is defining a language. It does tell you, a terminal expression is either a variable name or "a constant relation"--a literal denoting a relation value. $\endgroup$
    – philipxy
    Jun 3, 2021 at 5:36

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