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BACS485 – E/R to Relational Notation1 BACS 485 Translating E/R to Relational Notation

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BACS485 – E/R to Relational Notation2 Relational Notation Relational Notation is a shorthand way to represent E/R diagrams. It is a half-way step between an abstract tool (i.e., E/R diagrams) and an implementation specific tool (i.e., SQL Create Table commands). The format is as follows: Table-name(key-attribute, attribute-1,… attribute-N)

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BACS485 – E/R to Relational Notation3 Relational Notation The basic rules of translating E/R diagrams to Relational Notation are given below: l Each entity becomes a table l Each attribute on the table becomes an attribute on the table l Primary keys are underlined l Foreign keys are underlined with a dashed line l In 1:1, the foreign key can be on either side of the relation (context dependent) l In 1:N, the foreign key goes on the N side l In M:N, the relation becomes a table and the key for the new table is the concatenated primary keys of the original tables l In sub-type/super-type, the primary key of the sub-type(s) is the same as the super-type (thus, no foreign key)

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BACS485 – E/R to Relational Notation4 1:1 E/R to Relational Notation l Translates to 2 tables: Table1 (A,B,C,D) OR Table1 (A,B,C) Table2 (D,E,F) Table2 (D,E,F,A) pick one depending upon context, dashed underlined letter is foreign key

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BACS485 – E/R to Relational Notation5 1:1 Relational Notation to E/R l Translate from 2 tables: Table1 (X,Y,Z) OR Table1 (X,Y,Z,L) Table2 (L,M,N,X) Table2 (L,M,N) pick one depending upon context, dashed underlined letter is foreign key

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BACS485 – E/R to Relational Notation6 1:N E/R to Relational Notation l Translates to 2 tables: Table1 (A,B,C) Table2 (D,E,F,A) dashed underlined letter is foreign key

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BACS485 – E/R to Relational Notation7 1:N Relational Notation to E/R l Translate from 2 tables: Table1 (X,Y,Z,L) Table2 (L,M,N) dashed underlined letter is foreign key

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BACS485 – E/R to Relational Notation8 Simple M:N E/R to Relational Notation l Translates to 3 tables: Table1 (A,B,C) Table2 (D,E,F) Table3 (A,D) Notice that there is no foreign key

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BACS485 – E/R to Relational Notation9 Simple M:N Relational Notation to E/R l Translate from 3 tables: Table1 (X,Y,Z) Table2 (L,M,N) Table3 (X,L)

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BACS485 – E/R to Relational Notation10 More Complex M:N E/R to Relational Notation l Translates to 3 tables: Table1 (A,B,C) Table2 (D,E,F) Table3 (A,D,X) Notice that relationship attribute is attached to new table

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BACS485 – E/R to Relational Notation11 More Complex M:N Relational Notation to E/R l Translate from 3 tables: Table1 (X,Y,Z) Table2 (L,M,N) Table3 (X,L,P)

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BACS485 – E/R to Relational Notation12 More Complex M:N E/R to Relational Notation l Translates to 3 tables: Table1 (A,B,C) Table2 (D,E,F) Table3 (A,D,X) Notice that relationship attribute is attached to new table

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BACS485 – E/R to Relational Notation13 More Complex M:N E/R to Relational Notation l Translates to 4 tables: Table1 (A,B,C) Table2 (D,E,F) Table3 (H,I,J) Table4 (A,D,H,K)

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BACS485 – E/R to Relational Notation14 Sub-Type / Super-Type E/R to Relational Notation l Translates to 3 tables: Table1 (A,B,C) Table2 (A,D,E,F) Table3 (A,H,I,J) Notice that Table2 and Table3 do not have a key in the E/R.

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