RDBMS
- 1. M. DHARANI M.SC (CS), NADAR SARASWATHI COLLEGE OF ARTS & SCIENCE,THENI.
- 2. INDEX oDEFINITION oUSE OF ENTITY SETS VERSUS ATTRIBUTES oUSE OF ENTITY SETS VERSUS RELATIONSHIP SETS oBINARY VERSUS N-ARY RELATIONSHIP SETS oPLACEMENT OF RELATIONSHIP ATTRIBUTES
- 3. DEFINTION oThe notions of a entity set and a relationship are not precise, and it is possible to define a set of entities and the relationship among them in a number of different way. oBasic example issues in the design of an ER diagram schema.
- 4. USE OF ENTITY SETS VERSUS ATTRIBUTES oThe entity set employee with attributes employee-name and telephone-number. oIt can easily be argued that a telephone in an entity in its own right with attributes telephone- number and location.
- 5. If you can this point of view, must redefine the employee entity set as: oThe employee entity set with attributes employee-name. oThe telephone entity set with attributes telephone-number and location. oThe relationship set emp-telephone, which denotes the association between employees and the
- 6. oTreating a telephone as an attributes telephone number implies that employee have precisely one telephone number each. oA common mistake is to use the primary key of an entity set as an attributes of an other entity set, instead of using a
- 7. USE OF ENTITY SETS VERSUS RELATIONSHIP SETS oAn alternatives is to model a loan not as an entity, but rather as a relationship between customers and branches, with loan number and amount as descriptive attributes. oIf every loan is held by exactly one customer and is association with exactly one branch. oWe may find satisfactory the design
- 8. BINARY VERSUS N-ARY RELATIONSHIP SETS oRelationship in database are often binary. oSome relationships that appear to be nonbinary could actually be better represented by several binary relationships. oIt is always possible to replace a nonbinary(n- ary, for n>2) relationship set by a number of distinct binary
- 9. We replace the relationship set R by an entity set E, and create three relationship sets: oRa, relation E and A oRb, relation E and B oRc, relation E and C oIf the relationship set R had any attributes, these are assigned to entity set E.
- 10. Relationship( ai, bi, ci )in the relationship set R, we create a new entity ei in the entity set E o(ei, ai) in Ra o(ei, bi) in Rb o(ei, ci) in Rc oWe can generalize this process in a straightforward manner to n- ary relationship sets.
- 11. we can restrict the E-R model to include only binary relationship sets oAn identifying attributes may have to be created for the entity set created to represent the relationship sets. oA n-ary relationship set shows more clearly that several entities participate in a single relationship. oThere may not be a way to translate constraints on the ternary relationship into constraints on the binary
- 12. PLACEMENT OF RELATIONSHIP ATTRIBUTES oThe cardinality ratio of a relationship can affect the placement of relationship attributes. oThus, attributes of one-to-one or one- to-many relationship sets can be associated with one of the participating entity sets, rather than with the relationship set.
- 13. Access-date as attributes of the account entity set Depositor JOHNSON SMITH HAYES TURNER JONES A-101 24 May 1996 A-215 3 June 1996 A-102 10 June 1996 A-305 28 May 1996 A-201 17 June 1996 A-222 24 June 1996
- 14. Thank you