Database Design & Deployment

Transcription

1 ICS 321 Data Storage & Retrieval High Level Database Models Prof. Lipyeow Lim InformaCon & Computer Science Department University of Hawaii at Manoa Lipyeow Lim - - University of Hawaii at Manoa 1

2 Database Design & Deployment Requirements Analysis Conceptual Database Design Business Processes Logical Database Design Physical Database Design (DDL/DML) SQL OperaCons & program code iterate TesCng ProducCon Lipyeow Lim - - University of Hawaii at Manoa 2

3 Overview Database Design Conceptual Design Use encty- relaconship (aka ER) model represented pictorially as ER diagrams Map ER model to relaconal schema QuesCons to ask yourself What are the encces and relaconships in the applicacon? What informacon about these encces and relaconships should we store in the database? What are the integrity constraints or business rules that hold? Lipyeow Lim - - University of Hawaii at Manoa 3

4 ER Model Basics: ssn name lot EnCCes Employees! En#ty: Real- world object discnguishable from other objects. An encty is described (in DB) using a set of a)ributes.! En#ty Set: A colleccon of similar encces. E.g., all employees.! All encces in an encty set have the same set of axributes. (UnCl we consider ISA hierarchies, anyway!)! Each encty set has a key.! Each axribute has a domain. Lipyeow Lim - - University of Hawaii at Manoa 4

5 ER Model Basics: RelaConships ssn name lot since did dname budget Employees Works_In Departments! Rela#onship: AssociaCon among two or more encces.! Rela#onship Set: CollecCon of similar relaconships.! An n- ary relaconship set R relates n encty sets E1... En; each relaconship in R involves encces e1 E1,..., en En! Same encty set could parccipate in different relaconship sets, or in different roles in same set. Lipyeow Lim - - University of Hawaii at Manoa 5

6 Cardinality RaCos of RelaConships! Consider binary relaconships, i.e., between two encty sets! Alternate notacon: 1:1, 1:M, M:1, M:N 1-to-1 1-to Many Many-to-1 Many-to-Many Lipyeow Lim - - University of Hawaii at Manoa 6

7 Key Constraints ssn name lot since did dname budget Employees Manages Departments Works_In since! Consider Works_In: An employee can work in many depts; a dept can have many employees : m- to- m! Consider Manages: each dept has at most one manager! Dept has a key constraint on Manages: each instance of dept appears in at most one instance of manages! Denoted by an arrow: given a dept encty we can uniquely idencfy the manages relaconship in which it appears Lipyeow Lim - - University of Hawaii at Manoa 7

8 ParCcipaCon constraints name since dname ssn lot did budget Employees Manages Departments! Does every dept have a manager?! If so, this is a par#cipa#on constraint: the parccipacon of dept in Manages is said to be total (vs. par#al). Denoted by thick/double line! Meaning that every Dept encty must appear in an instance of the Manages relaconship Lipyeow Lim - - University of Hawaii at Manoa 8

9 Set TheoreCc FormulaCon A B C D Employees Manages (1:m) Departments ParCal ParCCcipaCon: Not all members of the Employees encty set take part in the manages relacons Total ParCCcipaCon: All members of the Dept encty set take part in the manages relaconship Dept has a key constraint on Manages: each member of the dept encty set takes part in at most one member of the manages relaconship set Lipyeow Lim - - University of Hawaii at Manoa 9

10 Weak EnCCes name ssn lot cost pname age Employees Policy Dependents! A weak en#ty can be idencfied uniquely only by considering the primary key of another (owner) encty.! Owner encty set and weak encty set must parccipate in a one- to- many relaconship set (one owner, many weak encces).! Weak encty set must have total parccipacon in this iden#fying relaconship set.! Denoted by a box with double or thick lines Lipyeow Lim - - University of Hawaii at Manoa 10

11 Design Choices! Should a concept be modeled as an encty or an axribute?! Should a concept be modeled as an encty or a relaconship?! IdenCfying relaconships: Binary or ternary? AggregaCon?! How much semanccs to capture in the form of constraints? Lipyeow Lim - - University of Hawaii at Manoa 11

12 EnCty vs. AXribute address Employee Employee has address! Depends upon how we want to use the address informacon, and the semanccs of the data: - If we have several addresses per employee, address must be an encty (since axributes cannot be set- valued). - If the structure (city, street, etc.) is important, e.g., we want to retrieve employees in a given city, address must be modeled as an encty (since axribute values are atomic). Lipyeow Lim - - University of Hawaii at Manoa 12

13 Logical DB Design: ER to RelaConal EnCty sets to tables: ssn name Employees lot CREATE TABLE Employees (ssn CHAR(11), name CHAR(20), lot INTEGER, PRIMARY KEY (ssn)) Lipyeow Lim - - University of Hawaii at Manoa 13

14 RelaConship Sets to Tables AXributes of the relacon must include: Keys for each parccipacng encty set (as foreign keys). This set of axributes forms a superkey for the relacon. All descripcve axributes. ssn name Employees CREATE TABLE Works_In( ssn CHAR(11), did INTEGER, since DATE, PRIMARY KEY (ssn, did), FOREIGN KEY (ssn) REFERENCES Employees, FOREIGN KEY (did) REFERENCES Departments) lot since Works_In did dname budget Departments Lipyeow Lim - - University of Hawaii at Manoa 14

15 TranslaCng ER Diagrams with Key Constraints ssn since did Employees Manages Departments A B C D Map relaconship to a table: Note that did is the key now! Since each department has a unique manager, we could instead combine Manages and Departments. Emp. Manages (1:m) Depts CREATE TABLE Manages( ssn CHAR(11), did INTEGER, since DATE, PRIMARY KEY (did), FOREIGN KEY (ssn) REFERENCES Employees, FOREIGN KEY (did) REFERENCES Departments) CREATE TABLE Dept_Mgr( did INTEGER, dname CHAR(20), budget REAL, ssn CHAR(11), since DATE, PRIMARY KEY (did), FOREIGN KEY (ssn) REFERENCES Employees) Lipyeow Lim - - University of Hawaii at Manoa 15

16 ParCcipaCon Constraints in SQL We can capture parccipacon constraints involving one encty set in a binary relaconship, but lixle else (without resorcng to CHECK constraints). CREATE TABLE Dept_Mgr( did INTEGER, dname CHAR(20), budget REAL, ssn CHAR(11) NOT NULL, since DATE, PRIMARY KEY (did), FOREIGN KEY (ssn) REFERENCES Employees, ON DELETE NO ACTION) Lipyeow Lim - - University of Hawaii at Manoa 16

17 TranslaCng Weak EnCty Sets Weak encty set and idencfying relaconship set are translated into a single table. When the owner encty is deleted, all owned weak encces must also be deleted. CREATE TABLE Dep_Policy ( pname CHAR(20), age INTEGER, cost REAL, ssn CHAR(11) NOT NULL, PRIMARY KEY (pname, ssn), FOREIGN KEY (ssn) REFERENCES Employees, ON DELETE CASCADE) Lipyeow Lim - - University of Hawaii at Manoa 17

18 ISA Hierarchies As in C++, or other PLs, axributes are inherited. If we declare A ISA B, every A encty is also considered to be a B encty. hourly_wages ssn hours_worked Hourly_Emps name lot Employees ISA contrac9d Contract_Emps Overlap constraints: Can Joe be an Hourly_Emps as well as a Contract_Emps encty? (Allowed/disallowed) Covering constraints: Does every Employees encty also have to be an Hourly_Emps or a Contract_Emps encty? (Yes/no) Lipyeow Lim - - University of Hawaii at Manoa 18

19 TranslaCng ISA Hierarchies to RelaCons General approach: 3 relacons: Employees, Hourly_Emps and Contract_Emps. Hourly_Emps: Every employee is recorded in Employees. For hourly emps, extra info recorded in Hourly_Emps (hourly_wages, hours_worked, ssn); must delete Hourly_Emps tuple if referenced Employees tuple is deleted). Queries involving all employees easy, those involving just Hourly_Emps require a join to get some axributes. AlternaCve: Just Hourly_Emps and Contract_Emps. Hourly_Emps: ssn, name, lot, hourly_wages, hours_worked. Each employee must be in one of these two subclasses. Lipyeow Lim - - University of Hawaii at Manoa 19

20 Unified Modeling Language Standardized general- purpose modeling language for sonware design Based on object- oriented model Class diagrams Lipyeow Lim - - University of Hawaii at Manoa 20

21 UML Classes Class name length year Ctle Movies genre Methods seccon typically not used in data modeling ER Entity Set UML Class Lipyeow Lim - - University of Hawaii at Manoa 21

22 AssociaCons Cardinality constraints : one instance of Stars can be connected to at least 0 instance of movies and at most inifinite instances of movies Lipyeow Lim - - University of Hawaii at Manoa 22

23 ReferenCal Integrity AggregaCon: Must be 0..1 (includes 1..1) ComposiCon : Must be 1..1 Every president runs exactly one studio AggregaCon never named Lipyeow Lim - - University of Hawaii at Manoa 23

24 AssociaCon Classes Lipyeow Lim - - University of Hawaii at Manoa 24

25 Sub- Class Hierarchies Lipyeow Lim - - University of Hawaii at Manoa 25

26 Modeling Tips Faithful to the semanccs of the applicacon Model only what is needed in the applicacon Minimize redundancy (why?) Simple is good If the model is geong too complicated, take a step back and ask Am i conceptualizing the right encces? Am i thinking of the right relaconships? Should some relaconships become encces? Vice versa? Should some axributes become encces? Vice versa? Lipyeow Lim - - University of Hawaii at Manoa 26