数据库 chp4_sql_oo.pdf

第四章ODL/OQL与SQL 3 面向对象数据库系统(Object Orient Database System OODBS) 一、三个发展方向: 1.扩展关系模型(Sybase/Oracle/DB2/Informix) 2.面向对象程序设计语言(C++,smalltalk) 3.面向对象数据库系统(法国O2,美国Itasca) 二、OO模型概念 1. Object对象和对象标识OID(全局唯一，不是key) object identifer OID永久持久性，从记录到对象，提高版本管理和动态模式修改 2. 封装(Encapsulation): 状态(属性)+行为(操作)=对象 对象实现和应用隔离,消息沟通 查属性通过调用(object.sno)，失去关系数据库优点，需要妥协 3. Class类:共享同样属性和方法的所有对象构成一个对象类,型 对象为值,是类的实例,类的属性可以类自身 4.类层次(结构) 子类和超类 继承:单继承和多重继承(在职博士:学生和老师) 嵌套:对象的属性是对象 5.消息(Message) 对象与外界通信方式 三、SQL3 SQL99:加入OODB许多特征-代替关系数据库霸主地位还需要不断改进 OQL Bring the best of sql into the OO world SQL3 Bring the best of OO into the relational world;ADT(abstract data types) OQL:embeded,shares the same programming and data model(C++,smalltalk java) SQL interface,values to be passed; ADTuse external functions SQL3 relations remain central,ADT’s new types OQL sets and bags of objects or structures 封装) SQL3 row type not; ADT’s are encapsulated in the usual sense OQL ODL classes are very close to SQL3 ADT’s OQL a single extent maintained for each class; member or members of this extent SQL3 an extent for a row type,a relation containing every existing tuple of that type (易变性retains its object identity, ODLwithin surrounding programming language,not through OQL applied to their values a new value interface Movie -class (extent movies key(title,year)) -analogous to the name of relation { attribute string title; attribute integer year; attribute integer length; attribute enumeration(color,blackandwhite) filmtype; relationship setstar stars inverse star::starredin; relationship studio ownedby inverse studio::owns; float lengthinhours() raises(nolengthf