Databases CIS 422

Lifetime of Data Transient results to the evaluations of expression Variables involved in procedure activation Global variables Dynamically allocated variables Data that exists between executions Data that exits between versions Data that outlives a program

Essentials to Provide Persistence Object ID Properties and relationships Scale of the store Stability of the store

Database vs File System Marketing Engineering Accounting DBMS Database Sales Accounts Employee Inventory Customer Parts Engineering Marketing Accounting Parts Customer Inventory Accounts

Database A collection of related data Represents some aspect of the real world Is a logically coherent collection of data with some inherent meaning Is designed, built, and populated with data for a specific purpose.

Database Management Systems Data Schema Program Independence Views

Hierarchical Model Motor Vehicle BusTruckCar

Network Model Customer Soup Order

Relational Model Soup-ID Soup Name Price Cust-ID Name Address Phone Order-ID Soup-ID Cust-ID Qty

Database Interface Approaches Data Definition Language CREATE TABLE inventory (inventory-number CHAR(20)NOT NULL description CHAR(25)NOT NULL price DECIMAL (9,2) Data Manipulation Language

Shareability Transactions Commit Abort Atomicity

Concurrency Locking Conservative Locking Policy Read Locks Write Locks

Object Oriented vs Traditional Objects are active components OO Databases have inheritance Allow storage in the form of objects

OODBMS - OO Part The system must support complex objects Object identity must be supported Objects must be encapsulated The system must support types or classes The system must support inheritance The system must avoid premature binding The system will be computationally complete The system must be extensible

OODBMS - DB Part It must be persistent, able to remember object state It must be able to manage very large databases It must accept concurrent users It must be able to recover from hardware and software failures Data query must be simple

Complex Objects Job Object OID eee Emp# E001 PositionSalary 50,000 ENAME Smith DEPT# D01 Budget 1,000,000 DNAME Mktg MgrEmpsOID ddd OID sss …... OID’s of Employee Objects

Object Data Management Group Model Parts Literals Objects (OID) –system assigned –not dependent on attribute values –conceptual address Collections

Abstract Types - Interfaces Inherit signatures of operations Noninstantiable Behaviour Inheritance –Supertype must be an interface –Subtype may be interface or class

Classes Specifies both attributes and behavior Instantiable Class Inheritance –supertype must be a class –subtype must be a class

Relationships Inverses 1-1 n-1 n-m

Persistent Objects Naming & Extents Reachablility Key

Company Schema Worker calcDeductions calcPay Employee string name string ssn int dependents Salaried double salary Hourly double hours double rate department n1 office 11

Representation interface Worker { method double calcDeductions(); method double calcpay(); }; class Employee : Worker ( extent workers key ssn) { atttribute string name attribute string ssn attribute int dependents relationship Department worksIn inverse Department::hasEmployees relationship Office residesAt inverse Office::houses }

Representation Continued class Salaried extends Employee ( extent salaried) { attribute double salary } class Department ( extent departments key number) { attribute int number attribute string name relationship set hasEmployees inverse Employee::worksIn }

Table-Class Mapping costcolormakemodelcar Cost color make model

Table-Multiple Classes Mapping nameaddresscustIDempID Employee name address empID Customer name address custID

Table-Inheritance Classes Mapping Employee name ssn address HourlyEmp wage SalariedEmp salary nameaddressssnwagesalary

Instance Relationships NameDepartmentID Name deparmentID ssn salary Department name departmentID Employee name salary ssn

Client Sends message to server Manages user interface –validate data –dispatch requests Solution specific logic GUI

Server Fulfills the client request Usually does database access functions File server Transaction server Located separate from client

Basic Characteristics of Client-Server Apps Front-end client acts with back-end server The two tasks have fundamentally different needs Environment is generally heterogeneous and multivendor Scalability

Common Components User Interface Business Processing Database Processing

Distributed Processing Processing divided up between processes Objects can be distributed and accessed by users across a network