Tài liệu Database Systems: The Complete Book- P2 doc

Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. [...]... placing in each of their declarations the keyword inverse and the name of the other relationship If the other relationship is in some other class, as it usually is, then we refer to that relationship by the name of its class, followed by a double colori (: :) and the name of the relationship Example 4.5: To define the relationship s t a r r e d I n of class S t a r to be the inverse of the relationship... are independent of the values of all the other attributes in the relation More precisely, we say the MVD holds for a relation R if when we restrict ourselves to the t u ~ l e of R that have s particular values for each of the attributes among the A's, then the set of values we find among the B's is independent of the set of values we find among the attributes of R that are not among the A's or B's Still... let the first tuple be t and the second be u, then the S,IVD asserts that we must also find in R the tuple that has name C Fisher, a street and city that agree with the first tuple, and other attributes ( t i t l e and ear) that agree with the second tuple There is indeed such a tuple; it is the third tuple of Fig 3.29 u Similarly, we could let t be the second tuple above a ~ i d be the first Then the. .. following the decomposition rule, using the above FD The first schema of the decomposition is the attributes of ' CHAPTER 3 THE RELATIONAL DATA lVODEL the FD itself, that is: {studioName,studioAddr) The second schema is all the attributes of Moviestudio except for studiohddr,because the latter attribute is on the right of the FD used in the decomposition Thus, the other schema is: {title, year, length,... i t y ) {theater, t i t l e ) There is a proble~n with this decomposition, concerning the FD t i t l e city + theater There could be current relations for the deconiposed schemas that satisfy the FD theater -+ c i t y (which can be checked in the relation {theater, c i t y ) ) but that, when joined, yield a relation not satisfying t i t l e c i t y -+ theater For instance, the two relations The intent... task groups Person The information we wish to record about persons includes their name (an atbribute) and the following relationships: mother, father, and children Give an ODL design for the Person class Be sure to indicate the inverses of the relationships that, like mother, father, and children, are also relationships from Person to itself Is t,he inverse of the mother relationship the children relationship?... implies 3KF are the result of the decomposition In each schema there are no ~lontrivial multivalued (or functional) dependencies, so they are in 4NF Note that in the relation with schema {name, s t r e e t , c i t y ) , the I\.IVD: Another way to compare the normal forms is by the guaantees they make about the set of relations that result from a decomposition into that normal form These observations... i t l e , the name of a movie 2 theater, the name of a theater where the movie is being shown 3 c i t y , the city where the theater is located Now we immediately see a BCNF violation l i e were given functional dependency theater -+ c i t y , but its left side, theater, is not a superkey We are t,herefore tempted to decompose, using this BCSF-violating FD, into the two relation schemas: {theater, c... is just D,while the type of the relationship in D is Set 3 If the relationship is many-one from D to C , then the roles of C and D are reversed in (2) above 4 If the relationship is one-one, then the type of the relationship in C is just D, and in D it is just C Note, that as in the E/R model, we allow a many-one or one-one relationship to include the case where for some objects the "one" is actually... ~ ~ in relation Rt then Ald2 - An + Cl Cz Ck also holds in R : If some of the C's are among the A's, we may eliminate them from the right side by the trivial-dependencies rule To see why the transitive rule holds, apply the test of Section 3.5.3 To test whether AlA2 - An + ClC2 Ck holds, we need to compute the closure {A1, A2, , A , } + with respect to the two given FD's TheFDdlA2 ,.An -+