Attribute analysis between object database system and relational database

In this paper, many netizens on the object database system and relational database system of confusion between the detailed analysis.

Object-oriented database system

Object oriented data base system, referred to as Oodbs, is a product of the combination of database technology and object-oriented programming method.

The research of OO data model and object-oriented database system is mainly embodied in: research on extended relation model based on relational database and SQL, research on persistent programming language based on object-oriented programming language, Support OO model, build new object-oriented database system, support OO data model.

Object-Oriented programming method is a practical and feasible programming method to support modular design and software reuse. It focuses the main activities of programming on establishing the connection (or communication) between objects and objects, thus completing the required calculations. An object-oriented program is a collection of objects that are interconnected (or communicated). The basic idea of object-oriented programming is encapsulation and scalability.

Object-oriented database systems support object-oriented data models (hereinafter referred to as OO models). Object-oriented database system is a persistent, shareable object library storage and management; An object library is a collection of objects defined by an OO model.

An OO model is a model that describes the logical organization of real-world entities (objects), the constraints between objects, and so on, in object-oriented perspective. A series of object-oriented core concepts form the basis of OO model. To sum up, the core concepts of the OO model are as follows:

(1) Object and Object identity OID (objects IDentifier).

Any entity in the real world is uniformly modeled as an object, each with a unique identity called the object Identifier (OID).

(2) Encapsulation (encapsulation).

Each object is an encapsulation of its state and behavior, where the state is a collection of a set of attribute values for that object, and the behavior is a collection of operations on the state of the object, also known as method.

(3) class (C1ass).

All objects that share the same attributes and set of methods form an object class (abbreviated Class), and an object is an instance of a class (instance).

(4) class hierarchy (structure).

In an object-oriented database schema, you can define subclasses (such as C2) of a class (such as C1), and the class CL is called a superclass (or parent class) of class C2. Subclasses, such as C2, can also redefine subclasses such as C3. Thus, a set of classes of object-oriented database schemas form a finite hierarchy, called class level.

(5) message.

Because objects are encapsulated, objects and external communications generally can only be passed through explicit messaging, that is, messages are passed externally to objects, properties and methods in the object are accessed and invoked, the required operations are executed internally, and the result of the operation is returned as a message.

The Oodb language is used to describe object-oriented database schemas, and to illustrate and manipulate class definitions and object instances. The Oodb language mainly includes object definition language (ODL) and Object Manipulation Language (OML), and an important subset of object manipulation language is Object Query Language (OQL). Oodb languages generally should have the following functions:

(1) Definition and manipulation of classes.

Object-oriented database languages can manipulate classes, including defining, generating, accessing, modifying, and revoking classes. The definition of a class includes defining the properties, operating characteristics, inheritance, and constraints of the class.

(2) The definition of operation/method.

Object-oriented database language can be used for the definition and implementation of object operations/methods. In operational implementations, language commands can be used to manipulate local data structures of objects. Encapsulation in the object model allows the operation/method to be implemented by different programming languages and hides the fact that different programming languages are implemented.

(3) The manipulation of the object.

Object-oriented database language can be used to manipulate (i.e. build, access. Modify and delete) instance object.

At present, there is no standard for object-oriented database language like SQL, so different OODBMS their specific database language.

Object Database System

Object-relational database system combines the characteristics of relational database system and object-oriented database system. In addition to the characteristics of the original relational database, the object-relational database system should also provide the following features:

(1) Expand data types, such as arrays, vectors, matrices, collections, and other data types, and operations on those data types.

(2) supports complex objects, i.e. objects consisting of a variety of basic data types or user-defined data types.

(3) Support the concept of inheritance.

(4) Provide common rules system, greatly enhance the function of object-relational database, so that it has the characteristics of active database and knowledge base.

Object Database VS relational database

We define the object database management system (ODBMS) as a database management system (DBMS) that integrates database capabilities with object-oriented programming language capabilities, and Odbms makes database objects look like programming languages in one or more programming languages that are already in place. Chairman of the--rick cattell,omg-93 Committee.

Odbms provides persistent storage in a multiuser client/server environment. Odbms can handle parallel access to objects, provide locking and transaction protection, protect object storage from various types of threats, and care for traditional tasks such as backup and recovery. Odbms this is so different from the relational database because Odbms stores objects, not tables. The reference to the object is made by persistent identity (PID), which uniquely identifies each object and can be used to establish a tag and container relationship between objects. Odbms also strengthens the encapsulation to support inheritance. Odbms combines object attributes and traditional DBMS functions such as locking, protection, transaction processing, querying, layout-oriented, concurrency, and persistence.