Database application requirements and Object relational database

A data management technology develops rapidly with the application progress

The development of application has always been the driving force for the progress of data management technology. In other words, application development and technological progress are mutually promoted and promoted. This is illustrated by a review of the history of the field of data management.

In the late 50 and the middle of the 60, the data management function is mainly implemented by the file system, only provides a relatively simple data access function, each file is independent of each other, do not have contact with each other, the system of data files to open the file, close the file, read/write a record from the file

However, with the development of applications, it is required to store and manage structured data, that is, not only managing the data itself, but also managing the relationship between the data, so as to provide a navigable query based on the links between the data, so that a large number of query application requirements can be directly satisfied by the system (without The database system was then produced in the late 60.

The data of database system management is structured, which provides powerful data query function and provides good data sharing. At that time, the database system mostly uses the hierarchical data model or the network data model. With the development of data management technology, in the early 70, the relational data theory was put forward, and the relational data method was established, and then the relational database system was born.

relational database system Management data, its structure is relatively simple, the data itself in the form of two-dimensional table storage; The data connection between tables is reflected by the connection between the Code of one table and the outer code of another table. The relational database system provides the powerful query function, provides the very convenient, the easy to use the non procedural Query language (has formed the relational database language International standard SQL), thus obtains the extremely widespread application, has greatly promoted the business data processing application the rapid development.

With the development of new applications such as CAD, case, image processing and GIS, as well as the deepening of applications in traditional applications (e.g., the need to process multimedia information), data management software is required to manage complex objects, and to simulate complex behaviors of complex objects (more complex operations are applied to data). Then, in the late 80, the Object-oriented database system was created, the object-oriented technology was combined with the database technology, the class facilities were used to describe the complex object, the complex behavior of the object was simulated by the encapsulation method in the class, and the object's structure and methods were reused by using the inheritance.

Object-oriented database system satisfies the application requirements of some specific application fields (such as CAD). However, this kind of pure object-oriented database system does not support SQL, has lost its advantage in generality, and its application field is restricted greatly. In the process of combining object-oriented technology and database technology, basically, it is developed along two ways: one is to establish a pure object-oriented database management system (i.e. Oodbms), which is often based on an object-oriented language, which increases the function of the database, mainly supports the persistent object and realizes the data sharing.

Another way is to expand from the traditional relational database, add object-oriented features, combine object-oriented technology with relational database, establish object-relational database management system (i.e. Ordbms), and Ordbms not only support the widely used SQL, but also have good versatility and object-oriented characteristics, Complex behavior that supports complex objects and complex objects.

The new SQL International standard being developed (now called SQL3) embodies the characteristics of the Ordbms. Ordbms adapts to the needs of some new application fields and the need of deepening development in traditional application field, so Ordbms has been developed rapidly in recent years.

Two. Application of requirements classification and data management software

Application requirements are the driving force for the development of database management system and other data management software.

Different application fields need to be managed in different data types and data complexity, the complexity of the query required for the data is different, the other operation of the data, and the requirements of data security, concurrency control and fault recovery are different.

No one kind of omnipotent data management software can satisfy all the application requirements, and can serve the different application fields effectively. Therefore, driven by application requirements, a wide variety of data management software has been developed and marketed.

Below, we classify the application requirements based on the complexity of the data and the complexity of the query requirements, and discuss the data management software suitable for all kinds of application requirements.

1. Simple data, simple query ——— file system

We use the text processing system as an example to describe the needs of this type of application. Word processing is an essential part of office work. Common body processing system has word, framemaker, Word Perfect, vi and so on. They work in a very simple way: The user opens the file by name, and the contents of the file are copied to the virtual store. When you edit the body, the virtual object is updated, and the object is periodically saved to the hard disk. Closes the file at the end of the body process, at which point the copy in the virtual save is saved back to the file system. The text processing system described above represents a class of application requirements that can be called simple data queries (or no query requirements). Its data structure is very simple, just a sequence of characters, and its query requirements are simpler, just reading and writing files. Therefore, for such applications, the file system provided by the operating system manufacturer is sufficient to satisfy its functional requirements and has high performance.