Database Modeling & Design Fourth Edition- P23 pdf

@Spy 5.1 Transformation Rules and SQL Constructs 97 Figure 5.6 UML: ternary and n-ary relationships Technician Project emp_id project_name notebook_no 35 alpha 5001 35 gamma 2008 42 delta 1004 42 epsilon 3005 81 gamma 1007 93 alpha 1009 93 beta 5001 Notebook 11 1 uses-notebook A technician uses exactly one notebook for each project. Each notebook belongs to one technician for each project. Note that a technician may still work on many projects and maintain different note- books for different projects. create table technician (emp_id char(10), primary key (emp_id)); create table project (project_name char(20), primary key (project_name)); create table notebook (notebook_no integer, primary key (notebook_no)); create table uses_notebook (emp_id char(10), project_name char(20), notebook_no integer not null, primary key (emp_id, project_name), foreign key (emp_id) references technician on delete cascade on update cascade, foreign key (project_name) references project on delete cascade on update cascade, foreign key (notebook_no) references notebook on delete cascade on update cascade, unique (emp_id, notebook_no), unique (project_name, notebook_no)); uses_notebook emp_id, project_name → notebook_no emp_id, notebook_no → project_name project_name, notebook_no → emp_id (a) one-to-one-to-one ternary association Functional dependencies Teorey.book Page 97 Saturday, July 16, 2005 12:57 PM @Spy 98 CHAPTER 5 Transforming the Conceptual Data Model to SQL Figure 5.6 (continued) emp_id project_name loc_name 48101 forest B66 48101 ocean E71 20702 ocean A12 20702 river D54 51266 river G14 51266 ocean A12 76323 hills B66 Each employee assigned to a project works at only one location for that project, but can be at a different location for a different project. At a given location, an employee works on only one project. At a particular location there can be many employees assigned to a given project. create table employee (emp_id char(10), emp_name char(20), primary key (emp_id)); create table project (project_name char(20), primary key (project_name)); create table location (loc_name char(15), primary key (loc_name)); create table assigned_to (emp_id char(10), project_name char(20), loc_name char(15) not null, primary key (emp_id, project_name), foreign key (emp_id) references employee on delete cascade on update cascade, foreign key (project_name) references project on delete cascade on update cascade, foreign key (loc_name) references location on delete cascade on update cascade, unique (emp_id, loc_name)); assigned_to (b) one-to-one-to-many ternary associations emp_id, loc_name → project_name emp_id, project_name → loc_name Functional dependencies Employee Project Location 11 * assigned-to Teorey.book Page 98 Saturday, July 16, 2005 12:57 PM @Spy 5.1 Transformation Rules and SQL Constructs 99 Figure 5.6 (continued) emp_idproject_name mgr_id 4106alpha 27 4200alpha 27 7033beta 32 4200beta 14 4106gamma 71 7033delta 55 4106delta 39 4106iota 27 Each engineer working on a particular project has exactly one manager, but a project can have many managers and an engineer may have many managers and many projects. A manager may manage several projects. create table project (project_name char(20), primary key (project_name)); (c) one-to-many-to-many ternary association create table manager (mgr_id char(10), primary key (mgr_id)); create table engineer (emp_id char(10), primary key (emp_id)); create table manages (project_name char(20), mgr_id char(10) not null, emp_id char(10), primary key (project_name, emp_id), foreign key (project_name) references project on delete cascade on update cascade, foreign key (mgr_id) references manager on delete cascade on update cascade, foreign key (emp_id) references engineer on delete cascade on update cascade); manages project_name, emp_id → mgr_id Functional dependency Project Manager Engineer 1* * manages Teorey.book Page 99 Saturday, July 16, 2005 12:57 PM @Spy 100 CHAPTER 5 Transforming the Conceptual Data Model to SQL Figure 5.6 (continued) emp_id project_nameskill_type 101 electronicsalgebra 101 electronicscalculus 101 mechanicsalgebra 101 mechanicsgeometry 102 electronicsalgebra 102 electronicsset-theory 102 mechanicsgeometry 105 mechanicstopology Employees can use different skills on any one of many projects, and each project has many employees with various skills. create table employee (emp_id char(10), emp_name char(20), primary key (emp_id)); create table skill (skill_type char(15), primary key (skill_type)); create table project (project_name char(20), primary key (project_name)); create table skill_used (emp_id char(10), skill_type char(15), project_name char(20), primary key (emp_id, skill_type, project_name), foreign key (emp_id) references employee on delete cascade on update cascade, foreign key (skill_type) references skill on delete cascade on update cascade, foreign key (project_name) references project on delete cascade on update cascade); skill_used (d) many-to-many-to-many ternary association None Functional dependencies Employee Skill Project ** * skill-used Teorey.book Page 100 Saturday, July 16, 2005 12:57 PM @Spy 5.1 Transformation Rules and SQL Constructs 101 5.1.4 Generalization and Aggregation The transformation of a generalization abstraction can produce separate SQL tables for the generic or supertype entity and each of the subtypes (Figure 5.7 for the ER model and Figure 5.8 for UML). The table derived from the supertype entity contains the supertype entity key and all com- mon attributes. Each table derived from subtype entities contains the supertype entity key and only the attributes that are specific to that sub- type. Update integrity is maintained by requiring all insertions and dele- tions to occur in both the supertype table and relevant subtype table— that is, the foreign key constraint cascade must be used. If the update is to the primary key of the supertype table, then all subtype tables, as well as the supertype table, must be updated. An update to a nonkey attribute affects either the supertype or one subtype table, but not both. The Figure 5.7 ER model: generalization and aggregation create table (indiv_id char(10),individual indiv_name char(20), indiv_addr char(20), primary key (indiv_id)); create table (emp_id char(10),employee job_title char(15), primary key (emp_id), foreign key (emp_id) references individual on delete cascade on update cascade); create table (cust_no char(10),customer cust_credit char(12), primary key (cust_no), foreign key (cust_no) references individual on delete cascade on u p date cascade); Individual An individual may be either an employee or a customer, or both, or neither. Employee Customer Teorey.book Page 101 Saturday, July 16, 2005 12:57 PM