Sarajane Marques Peres, Ph.D. University of São Paulo Based on Elsmari, Navathe / Silberschatz, Korth, Sudarshan s books

Transcription

1 Sarajane Marques Peres, Ph.D. University of São Paulo Based on Elsmari, Navathe / Silberschatz, Korth, Sudarshan s books ER MODEL à R MODEL

2 Mapping of Regular EnKty Types For each regular (strong) enkty type E in the ER schema, create a relakon R that includes all the simple apributes (or simple components of composite apributes) of E. Choose one of the key apributes of E as the primary key for R. If the chosen key of E is a composite, then the set of simple apributes that form it will together form de primary key of R.

3 Mapping of Regular EnKty Types For each regular (strong) enkty type E in the ER schema, create a relakon R that includes all the simple apributes (or simple components of composite apributes) of E. Choose one of the key apributes of E as the primary key for R. If the chosen key of E is a composite, then the set of simple apributes that form it will together form de primary key of R.

4 Mapping of Regular EnKty Types

5 Mapping of MulKvalued APributes For each mulkvalued apribute A, create a new relakon R. This relakon R will include an apribute corresponding to A, plus the primary key apribute K as a foreign key in R of the relakon that represents the enkty type or relakonship type that has A as a mulkvalued apribute. The primary key of R is the combinakon of A and K.

6 Mapping of MulKvalued APributes For each mulkvalued apribute A, create a new relakon R. This relakon R will include an apribute corresponding to A, plus the primary key apribute K as a foreign key in R of the relakon that represents the enkty type or relakonship type that has A as a mulkvalued apribute. The primary key of R is the combinakon of A and K.

7 Mapping of MulKvalued APributes Dname Dnumber Research 5 AdministraKon 4 Headquarters 1 Dnumber Dloca2on 1 Houston 4 Stafford 5 Bellaire 5 Sugarland 5 Houston

8 Mapping of Weak EnKty Types For each weak enkty type W in the ER schema with owner enkty type E, create a relakon R and include all simple apributes (or simple components of composite apributes) of W as apributes of R. Include as foreign key apribute(s) of R, the primary key apribute(s) of the relakons(s) that correspond to the owner(s) enkty type(s); The primary key of R is the combinakon of the primary key(s) of the owner(s) and the parkal key of the weak enkty type W, if any.

9 Mapping of Weak EnKty Types For each weak enkty type W in the ER schema with owner enkty type E, create a relakon R and include all simple apributes (or simple components of composite apributes) of W as apributes of R. Include as foreign key apribute(s) of R, the primary key apribute(s) of the relakons(s) that correspond to the owner(s) enkty type(s); The primary key of R is the combinakon of the primary key(s) of the owner(s) and the parkal key of the weak enkty type W, if any.

10 Mapping of Weak EnKty Types

11 Mapping of Binary 1:1 RelaKonship Types For each binary 1:1 relakonship type R in the ER schema, idenkfy the relakons S and T that correspond to the enkty types parkcipakng in R. Choose one approach: 1. The foreign key approach (most useful) 2. The merged relakonship approach 3. The cross- reference or relakonship relakon approach

12 Mapping of Binary 1:1 RelaKonship Types 1. Foreign key approach: Choose one of the relakons S, say and include as a foreign key in S the primary key of T. It is beper to choose an enkty type with total par2cipa2on in R in the role of S. Include all the simple apributes (or simple components of composite apributes) of the 1:1 relakonship type R as apributes of S.

13 Mapping of Binary 1:1 RelaKonship Types 1. Foreign key approach: Choose one of the relakons S, say and include as a foreign key in S the primary key of T. It is beper to choose an enkty type with total par2cipa2on in R in the role of S. Include all the simple apributes (or simple components of composite apributes) of the 1:1 relakonship type R as apributes of S. Mgr_ssn: APribute unique key!

14 Mapping of Binary 1:1 RelaKonship Types Using the same approach, but choosing the relakon T instead the relakon S. Dname Dnumber Research 5 AdministraKon 4 Headquarters 1 Fname Ssn Sex Mgr_dno Mgr- start- date John 1 M Franklin 2 M NULL NULL Alicia 3 F NULL NULL Jennifer 4 F NULL NULL Joyce 5 F NULL NULL Ahmed 6 M James 7 M

15 Mapping of Binary 1:1 RelaKonship Types Using the same approach, but choosing the relakon T instead the relakon S. Dname Dnumber Research 5 AdministraKon 4 Headquarters 1 Fname Ssn Sex Mgr_dno Mgr- start- date John 1 M Franklin 2 M NULL NULL Alicia 3 F NULL NULL Jennifer 4 F NULL NULL Joyce 5 F NULL NULL Ahmed 6 M James 7 M

16 Mapping of Binary 1:1 RelaKonship Types Using the same approach, but choosing the relakon T instead the relakon S. Dname Dnumber Research 5 AdministraKon 4 Headquarters 1 Fname Ssn Sex Mgr_dno Mgr- start- date John 1 M Franklin 2 M NULL NULL Alicia 3 F NULL NULL Jennifer 4 F NULL NULL Joyce 5 F NULL NULL Ahmed 6 M James 7 M

17 Mapping of Binary 1:1 RelaKonship Types Using the same approach, but choosing the relakon T instead the relakon S. Dname Dnumber Research 5 AdministraKon 4 Headquarters 1???? Mgr???? Fname Ssn Sex Mgr_dno Mgr- start- date John 1 M Franklin 2 M NULL NULL Alicia 3 F NULL NULL Jennifer 4 F NULL NULL Joyce 5 F NULL NULL Ahmed 6 M James 7 M

18 Mapping of Binary 1:1 RelaKonship Types Using the same approach, but choosing the relakon T instead the relakon S. Dname Dnumber Research 5 AdministraKon 4 Headquarters 1???? Mgr???? Fname Ssn Sex Mgr_dno Mgr- start- date John 1 M Franklin 2 M NULL NULL Alicia 3 F NULL NULL Jennifer 4 F NULL NULL Joyce 5 F NULL NULL Ahmed 6 M James 7 M

19 Mapping of Binary 1:1 RelaKonship Types 2. Merged relakon approach: An alternakve mapping is to merge the two enkty types and the relakonship into a single relakon. This is possible when both parkcipakons are total, as this would indicate that the two tables will have the exact same number of tuples at all Kmes. 3. Cross- reference or relakonship relakon approach: The third opkon is to set up a third relakon R for the purpose of cross- referencing the primary keys of the two relakons S and T represenkng the enkty type. The relakon R will include the primary key apributes of S and T as foreign keys to S and T. The primary key of R will be one of the two foreign keys, and the other foreign key will be a unique key of R.

20 Mapping of Binary 1:N RelaKonship Types For each regular binary 1:N relakonship type R, idenkfy the relakon S that represents the parkcipakng enkty type at the N- side of the relakonship type; Include as foreign key in S the primary key of the relakon T that represents the other enkty type parkcipakng in R; Be careful! Include any simple apributes (or simple components of composite apributes) of the 1:N relakonship type as apributes of S.

21 Mapping of Binary 1:N RelaKonship Types Be careful! For each regular binary 1:N relakonship type R, idenkfy the relakon S that represents the parkcipakng enkty type at the N- side of the relakonship type; Include as foreign key in S the primary key of the relakon T that represents the other enkty type parkcipakng in R; Include any simple apributes (or simple components of composite apributes) of the 1:N relakonship type as apributes of S. A cross- reference approach is also possible.

22 Mapping of Binary 1:N RelaKonship Types

23 Mapping of Binary M:N RelaKonship Types For each binary M:N relakonship type R, create a new relakon S to represent R. Include as foreign key apributes in S the primary keys of the relakons that represent the parkcipakng enkty types; their COMBINATION will form the primary key of S. Also includes any simple apributes of the M:N relakonship type (or simple components of composite apributes) as apribute of S.

24 Mapping of Binary M:N RelaKonship Types For each binary M:N relakonship type R, create a new relakon S to represent R. Include as foreign key apributes in S the primary keys of the relakons that represent the parkcipakng enkty types; their COMBINATION will form the primary key of S. Also includes any simple apributes of the M:N relakonship type (or simple components of composite apributes) as apribute of S.

25 Mapping of Binary M:N RelaKonship Types

26 Mapping of Binary M:N RelaKonship Types

27 Mapping of Binary M:N RelaKonship Types

28 RelaKonal Model (complete)

29 Analysing

30 Mapping of N- ary RelaKonship Types For each n- ary relakonship type R, where n>2, create a new relakon S to represent R. Include as foreign key apributes in S the primary keys of the relakons that represent the parkcipakng enkty types. Include any simple apributes of the n- ary relakonship type (or simple components of composite apributes) as apributes of S. The primary key of S is usually a combinakon of all the foreign keys that reference the relakons represenkng the parkcipakng enkty types. If the cardinality constraints on any of the enkty types E parkcipakng in R is 1, then the primary key of S should no include the foreign key apribute that references relakon E corresponding to E. K N 1 N M M

31 Mapping of N- ary RelaKonship Types K N 1 N M M

32 Mapping of N- ary RelaKonship Types Sname A B Proj_name Alfa Beta Part_no 1 2 C Gama 3 Sname Proj_name Part_no Quan2ty A Alfa 1 20 A Alfa 2 20 B Alfa 1 20 B Beta 1 10 C Beta 1 20 C Beta 3 40

33 Mapping of N- ary RelaKonship Types Sname A B Proj_name Alfa Beta Part_no 1 2 C Gama 3 Sname Proj_name Part_no Quan2ty A Alfa 1 20 A Alfa 2 20 B Alfa 3 20 B Beta 1 10 C Beta 2 20 C Beta 3 40

34 Mapping of SpecializaKon or GeneralizaKon NotaKon: APrs(R): apributes of relakon R PK(R): primary key of R OpKons for Mapping SpecializaKon or GeneralizaKon: Convert each specializakon with m subclasses {S 1, S 2,, S m } and (generalized) superclass C, where the apributes of C are {k, a 1,, a n } and k is the (primary) key, into relakon schemas using one of the following opkons: OpKon A: MulKple relakons superclass and subclasses; OpKon B: MulKple relakons subclass relakons only; OpKon C: Single relakons with one type apribute; OpKon D: Single relakon with mulkple type apributes.

35 Mapping of SpecializaKon or GeneralizaKon OpKon A: MulKple relakons superclass and subclasses. Create a relakon L for C with apributes APrs(L) = {k, a 1,, a n } and PK(L) = k. Create a relakons L i for each subclass S i, 1 <= i <= m, with the apributes APrs(L i ) = {k} U {apributes of S i } and PK(L i ) = k. This opkon works for any specializakon (total or parkal, disjoint or overlapping).

36 Mapping of SpecializaKon or GeneralizaKon OpKon A: MulKple relakons superclass and subclasses. Create a relakon L for C with apributes APrs(L) = {k, a 1,, a n } and PK(L) = k. Create a relakons L i for each subclass S i, 1 <= i <= m, with the apributes APrs(L i ) = {k} U {apributes of S i } and PK(L i ) = k. This opkon works for any specializakon (total or parkal, disjoint or overlapping).

37 Mapping of SpecializaKon or GeneralizaKon OpKon A: MulKple relakons superclass and subclasses.

38 Mapping of SpecializaKon or GeneralizaKon OpKon B: MulKple relakons subclass relakons only. Create a relakon L i for each subclass S i, 1 <= i <= m, with the apributes APrs(Li) = {apributes of S i } U {k, a i,, a n } and PK(L i ) = k. This opkon only works for a specializakon whose subclasses are total. AddiKonally, it is only recommended if the specializakon has the disjointedness constraint. If the specializakon is overlapping, the same enkty may be duplicated in several relakons.

39 Mapping of SpecializaKon or GeneralizaKon OpKon B: MulKple relakons subclass relakons only. Create a relakon L i for each subclass S i, 1 <= i <= m, with the apributes APrs(Li) = {apributes of S i } U {k, a i,, a n } and PK(L i ) = k. This opkon only works for a specializakon whose subclasses are total. AddiKonally, it is only recommended if the specializakon has the disjointedness constraint. If the specializakon is overlapping, the same enkty may be duplicated in several relakons.

40 Mapping of SpecializaKon or GeneralizaKon OpKon B: MulKple relakons subclass relakons only.

41 Mapping of SpecializaKon or GeneralizaKon OpKon C: Single relakons with one type apribute. Create a single relakon L with apributes APrs(L) = {k, a 1,, a n } U {apributes of S i } U U {apributes of S i } U {t} and PK(L) = k. The apribute t is called a type (or discriminakng) apribute whose value indicates the subclass to which each tuple belongs, if any. This opkons works only for specializakon whose subclasses are disjoint, and has the potenkal for generakng many NULL values if many specific apributes exist in the subclasses.

42 Mapping of SpecializaKon or GeneralizaKon OpKon C: Single relakons with one type apribute. Create a single relakon L with apributes APrs(L) = {k, a 1,, a n } U {apributes of S i } U U {apributes of S i } U {t} and PK(L) = k. The apribute t is called a type (or discriminakng) apribute whose value indicates the subclass to which each tuple belongs, if any. This opkons works only for specializakon whose subclasses are disjoint, and has the potenkal for generakng many NULL values if many specific apributes exist in the subclasses.

43 Mapping of SpecializaKon or GeneralizaKon OpKon C: Single relakons with one type apribute.

44 Mapping of SpecializaKon or GeneralizaKon OpKon D: Single relakon with mulkple type apributes. Create a single relakon schema L with apributes APrs(L) = {k, a 1,, a n } U {apributes of S 1 } U U {apributes of S m } U {t 1, t 2,, t m } and PK(L) = k. Each t i, 1 <= i <= m, is a Boolean type apribute indicakng whether a tuple belongs to subclass S i. This opkon is used for a specializakon whose subclasses are overlapping (but will also work for a disjoint specializakon).

45 Mapping of SpecializaKon or GeneralizaKon OpKon D: Single relakon with mulkple type apributes. Create a single relakon schema L with apributes APrs(L) = {k, a 1,, a n } U {apributes of S 1 } U U {apributes of S m } U {t 1, t 2,, t m } and PK(L) = k. Each t i, 1 <= i <= m, is a Boolean type apribute indicakng whether a tuple belongs to subclass S i. This opkon is used for a specializakon whose subclasses are overlapping (but will also work for a disjoint specializakon).

46 Mapping of SpecializaKon or GeneralizaKon OpKon D: Single relakon with mulkple type apributes.

47 MulKlevel specializakon (or generalizakon)

48 MulKlevel specializakon (or generalizakon)

49 Sarajane Marques Peres, Ph.D. University of São Paulo Based on Elsmari, Navathe / Silberschatz, Korth, Sudarshan s books ER MODEL à R MODEL