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Math Help - n-ary relations and their applications

  1. #1
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    n-ary relations and their applications

    Can anybody do the following problem?
    I don't know how to go about doing it...

    Give an example to show that if R and S are both n-ary relations, then

    <br />
P_{i_1,i_2,...,i_m}(R \cap S) may be different from <br />
P_{i_1,i_2,...,i_m}(R) \cap   P_{i_1,i_2,...,i_m}(S)
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  2. #2
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    Quote Originally Posted by robocop_911 View Post
    Give an example to show that if R and S are both n-ary relations, then <br />
P_{i_1,i_2,...,i_m}(R \cap S) may be different from <br />
P_{i_1,i_2,...,i_m}(R) \cap   P_{i_1,i_2,...,i_m}(S)
    How does your text define P_{i_1,i_2,...,i_m}(S)?
    Please be complete in your answer.
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  3. #3
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    Quote Originally Posted by Plato View Post
    How does your text define P_{i_1,i_2,...,i_m}(S)?
    Please be complete in your answer.

    The projection P_{i_1,i_2,...,i_m} where  i_1 < i_2 < ... < i_m, maps the n-tuple  (a_1, a_2,..., a_n) to the m-tuple  (a_{i_1}, a_{i_2}, ..., a_{i_m}), where m <= n.

    In other words, the projection P_i1, i_2,..., i_m deletes n-m of the components of an n-tuple, levaing the i1th, i2th and imth components.
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  4. #4
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    Quote Originally Posted by robocop_911 View Post
    The projection P_{i_1,i_2,...,i_m} where  i_1 < i_2 < ... < i_m, maps the n-tuple  (a_1, a_2,..., a_n) to the m-tuple  (a_{i_1}, a_{i_2}, ..., a_{i_m}), where m <= n.

    In other words, the projection P_i1, i_2,..., i_m deletes n-m of the components of an n-tuple, levaing the i1th, i2th and imth components.

    For example:
    If  P_{1,3} is applied to a 4 tuple (2,3,0,4) gives (2,0)
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