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ODBMS what is object oriented database ? An object-oriented database management system (OODBMS), sometimes shortened to ODBMS for object database management system, is a database management system (DBMS) that supports the modelling and creation of data as objects ODBMS ODBMS includes some kind of support for classes of objects and the inheritance of class properties and methods by subclasses and their objects There is currently no widely agreed-upon standard for an OODBMS, and OODBMS products are considered to be still in their imature stage ODBMS In the meantime, the object-relational database management system (ORDBMS), the idea that object-oriented database concepts can be superimposed on relational databases, is more commonly available products An object-oriented database interface standard is being developed by an industry group, the Object Data Management Group (ODMG) ODBMS Object Data Management Group has set a standard for Object Databases (version 30) ODL - Object Definition Language OML - Object Manipulation Language ODBMS Typical Applications for ODBMS: - Computer-aided design (CAD) - Computer-aided software engineering (CASE) - Multimedia databases --- Images, video, games, etc - Office automation systems (OIS) - Expert database systems ODBMS OBJECT STRUCTURE Objects basically consist of the following: Attributes - Attributes are data which defines the characteristics of an object This data may be simple such as integers, strings, and real numbers or it may be a reference to a complex object Methods - Methods define the behavior of an object and are what was formally called procedures or functions ODBMS Attributes Contain current state of an object Attributes can be classified as simple or complex Simple attribute can be a primitive type such as integer, string, etc, which takes on literal values Complex attribute can contain collections and/or references Reference attribute represents relationship An object that contains one or more complex attributes is called a complex object ODBMS Object Identity Object identifier (OID) assigned to object when it is created that is: ± System-generated ± Unique to that object ± Invariant ± Independent of the values of its attributes (that is, its state) ± Invisible to the user (ideally) ODBMS Object Identity - Implementation In RDBMS, object identity is value-based: primary key is used to provide uniqueness Primary keys do not provide type of object identity required in OO systems: - key only unique within a relation, not across entire system; - key generally chosen from attributes of relation, making it dependent on object state ODBMS Methods and Messages Method ± Defines behavior of an object, as a set of encapsulated functions Message ± Request from one object to another asking second object to execute one of its methods ODBMS Object Showing Attributes and Methods Class Instance Share Attributes and Methods ODBMS Subclasses, Superclasses, and Inheritance ‡ All instances of subclass are also instances of superclass ‡ Principle of substitutability states that instance of subclass can be used whenever method/construct expects instance of superclass ‡ Relationship between subclass and superclass known as A KIND OF (AKO) relationship ‡ Four types of inheritance: single, multiple, repeated, and selective ODBMS Single Inheritance ODBMS Multiple Inheritance ODBMS Repeated Inheritance Class Hierarchy class person{ stringname; stringaddress: }; class customer isa person { int credit-rating; }; class employee isa person { date start-date; int salary; }; class officer isa employee { int office-number, int expense-account-number, }; ODBMS OODBMS vs RDBMS RDBMS have been around for more than 20 years, OODBMS are relatively new RDBMS can handle >10 to 107 10 records, OODBMS up OODBM good for storing complex descriptions (eg, a plant schematic), RDBMS appropriate for simple, ³flat´ data ODBMS OODBMS vs RDBMS RDBMS control the DB market (>90%), OODBMS own Returns a table with rows Example of OQL query Result of the query (SQL) Original table Product no P1 P2 P3 Name Ford Mustang Toyota Celica Mercedes SLK Color Black Green Black Result String Ford Mustang String Mercedes SLK - The statement queries a object-oriented database => Returns a collection of objects Comparison Queries look very similar in SQL and OQL, sometimes they are the same In fact, the results they give are very different Query returns: OQL Object Collection of objects SQL Tuple Table SQL3 ³Object-oriented SQL´ Foundation for several OO database management systems ORACLE8, DB2, etc New features relational & Object oriented Relational Features new data types, new predicates, enhanced semantics, additional security and an active database Object Oriented Features and procedures support for functions







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