General information about databases. History of the development of database management systems
- History of the appearance of DBMS. What are the causes of emergence the DBMS?
- What is the assignment of database management systems (DBMS)? What is a database?
- What are the main properties of database management systems?
- What trends influence the evolution of database management systems?
- What were the stages in the history of development and improvement of database management systems?
- What advantages and disadvantages did the first generation DBMS have?
- How (by what principles) relational DBMSs work?
- What are the advantages of using relational DBMSs in comparison with the first generation DBMS?
- By what principle do object-oriented DBMS work?
- What are the advantages and disadvantages of using object-oriented DBMS?
- What are hybrid object-relational DBMSs?
1. History of the appearance of DBMS. What are the causes of emergence the DBMS?
In the history of the use of computer technology, several areas of its use can be identified.
First of all, the means of computer technology were intended for solving complex mathematical problems, which require a large number of computations. Such tasks were impossible to calculate “manually” in a reasonable time. In this regard, computer technology has greatly facilitated the work of engineers, scientists, etc. To simplify the solution of such tasks, appeared:
- various numerical methods for solving problems;
- specialized algorithmic languages (for example, Fortran).
However, over time, the use of personal computers to perform complex scientific calculations has been supplanted by another direction of using computer aids. The following areas of computer technology have been developed:
- support for reliable information storage;
- execution of specific information transformations for a given application (program);
- user-friendly and easily digestible user interface;
- execution of specific (sometimes uncomplicated) calculations for a given application.
The development of this direction led to the fact that in the late 60s and early 70s specialized software was introduced, which became known as the DataBase Management System (DBMS).
2. What is the assignment of database management systems (DBMS)? What is a database?
The basis of any modern information system is a database management system. Database management systems are designed to process data in such a way that they can be conveniently operated. DBMS allows:
- systematize data in the database;
- organize data to store it on computers.
A database is a collection of some data that are organized according to certain conservation rules. Data storage and processing in the database can be built on the basis of interconnected schemes, tables, stored procedures, views and other complex objects (elements). The data representation in the database must correspond to the selected data model (for example, the relational data model, the object-oriented data model, etc.).
3. What are the main properties of database management systems?
For all existing database management systems, the following basic properties can be distinguished:
- support for a logically consistent set of files. Any database can consist of one or several files;
- providing Data Manipulation Language (DML). For example, modern relational database management systems support the SQL (Structured Query Language) language, which is the standard;
- the possibility of recovering information after it is lost in the event of a failure;
- ensuring the parallel operation of multiple users.
4. What trends influence the evolution of database management systems?
The evolution of database management systems is influenced by:
- the development of microelectronic technologies;
- the development of personal computers;
- development of digital mobile devices;
- development of the Internet.
5. What were the stages in the history of development and improvement of database management systems?
In the development history of the DBMS, three main stages can be distinguished.
Stage 1. This stage corresponds to the first-generation DBMS. Such database management systems had a hierarchical and network data models. These models were based on the CODASYL specifications. In the first-generation DBMS, information systems were based on mainframes-large computers (for example, IBM 360). DBMS of the first generation had a number of shortcomings in comparison with the DBMS of the following generations.
Stage 2. At this stage there are relational DBMSs (early 70s of the XX century). To date, relational databases are among the most popular. In such databases, information is stored in the form of tables, which are related to each other by relations.
Stage 3. This phase is characterized by the appearance of object-oriented DBMS, which are based on the use of the object-oriented database design paradigm.
6. What advantages and disadvantages did the first generation DBMS have?
Disadvantages of the first generation DBMS in comparison with the second generation DBMS:
- first-generation DBMSs were quite difficult to use;
- relatively strong dependence of the application systems on the physical organization of the database;
- there were no means of automation of database design;
- first-generation DBMSs had a high cost.
Advantages of the first generation DBMS:
- the first-generation DBMS had low-level data management facilities in external memory;
- they had the opportunity to build manually applied systems;
- had the opportunity to save memory by sharing objects.
7. How (by what principles) relational DBMSs work?
The ideology of relational DBMSs was developed by the mathematician E. Codd, who proposed the use of set theory for data processing. According to this theory, any representation of data is reduced to a set of two-dimensional tables, which are linked by relations.
In his theory E. Codd proposed two basic principles:
- In tables, the relationship between data is established on the basis of their internal logical relationships.
- In relational DBMS, a single instruction can process large amounts of information as well as entire data files. Before the advent of relational databases, in a first-generation DBMS, only one record was processed by one command.
8. What are the advantages of using relational DBMSs in comparison with the first generation DBMS?
Relational DBMSs have several advantages in comparison with the first generation DBMS:
- the form of information representation is convenient (natural) for the user;
- in relational DBMSs, you can create data manipulation languages that are convenient for managing the database;
- with the help of one command it is possible to process whole arrays of information (in contrast to the first generation DBMS);
- relational databases are based on the apparatus of set theory, in which operations on data are well described from the mathematical point of view.
9. By what principle do object-oriented DBMS work?
Object-oriented databases arose as a result of the development of relational databases in order to provide opportunities for solving more complex tasks. Object-oriented databases use the ideas of the object-oriented approach, which is close to the real world entities. At the heart of this approach is the concept of an object that can possess properties and behavior. You can use objects directly (without using tables). In the object-oriented paradigm, one’s own (complex) data types are formed.
10. What are the advantages and disadvantages of using object-oriented DBMS?
Advantages of object-oriented DBMS:
- such DBMS use an object-oriented approach, which in some cases is more efficient (for example, the development of corporate-level information systems) compared with the relational approach;
- partitioning the system into independent objects, for any of which an independent specification is defined;
- object-oriented DBMS supports heredity and polymorphism of objects, and this facilitates the further development of such DBMS;
- object-oriented DBMSs allow to perform object modeling, the advantage of which is a good tracking of the behavior of real entities of the subject area at the initial stages of development;
- in some cases, object-oriented DBMSs are more convenient for representing complex objects. In such DBMS, data and methods for changing complex objects are placed as a whole. For such objects, you do not need to decompose the data in order to present them in tables, as it is done in relational DBMSs.
Disadvantages of object-oriented DBMS:
- in most problems, the use of the object-oriented approach is superfluous. This applies to cases where the breakdown of a complex object into logical parts is not difficult. In this case, it is more appropriate to use a relational model to represent data;
- object-oriented DBMS, as a rule, is based on its own programming interface, in contrast to the relational DBMS, where there is a common (standardized) query language for all databases.
11. What are hybrid object-relational DBMSs?
Hybrid databases combine both of the above approaches: a relational approach and an object-oriented approach. For example, Oracle has an object-oriented superstructure over the relational kernel of the system.
- Functions of Database Management Systems (DBMS)
- Basic concepts of the relational data model
- Relational databases. The concept of a key. Types of keys. Relations. Master table and detail table