What is the name of the set of basic structural, functional components of various databases, DBMS (database management systems)? This complex in information science is called the database architecture , DBMS. We suggest that you thoroughly analyze this concept, the types of such complexes, their three-level partition.
What is it?
Database architecture is a complex of structural components of the database, as well as tools that ensure their interaction both with each other and with the end user, system personnel.
This definition reflects one of the most important functions of information storages - providing the possibility of abstraction of database information. It forms the current approach to data architecture.
This raises a new question: what is the essence, purpose of data abstraction? Provided by the system, they (abstractions) will be the main means of supporting the independence of maintaining information storages (in other words, databases) by different groups of end users. In another way, this is called system data independence.
Types of DB
The architecture of database management systems will vary depending on the variety of the latter. Today there are two types of databases:
With the features of each of the varieties, we invite the reader to read further.
Centralized databases
The main difference between these databases: they are stored in the memory of one computing system. But if the database, in turn, is a component of computer networks, then distributed access to the databases becomes possible. That is, the database will be open to users of electronic computers connected to this network. Such use is typical for local computer systems created on the basis of organizations and companies.
Distributed databases
What is important to know about distributed database architecture? Such databases consist of several parts stored in different computers of the same network. Perhaps the information here will be duplicated, intersect. Conveniently, the user of a distributed database does not need to know how the elements of the information store are located in the nodes of such a network. Most often, he perceives this complex of information as a whole.
How is work with a similar database carried out? Using a distributed database management system (RDBMS). Her system directory will describe the information contained in the data warehouse, the basics of its placement on the network. In turn, the directory itself can be decomposed, placed in various nodes of the shared network.
The components of a distributed database are placed on separate computers connected to it. They are managed by their own (local) DBMS of electronic computing devices. What is important to note, such local information storage management systems do not have to be the same in different nodes of the shared network. However, combining such various local databases into a single system is a very difficult scientific and technical task. For its successful solution, a whole complex of experimental measures and theoretical developments was required.
Types of DB by the method of access to them
The database architecture will also vary in how they access the information in the repository:
- Local access.
- Remote access (network).
The last type of access involves dividing the architecture of such systems into two more variations:
- Type "file server".
- Type "client server".
Again, we offer the reader to deal with the presented varieties in more detail.
DB "file server"
A similar architecture of database complexes involves the allocation of one of the devices of the computer network as a central one. It will be considered a file server. A shared centralized database is stored on the host machine. Other network devices act as workstations that support user access to the main database.
In the "file server" system, each user has the ability to run an application located on the main machine. Moreover, only a copy of this program will be opened on his device.
By user requests, the files of the central database (located on the server) are transferred to computers - workstations. There is information processing. For users working with a common database, a local copy of it appears on computers. The latter is periodically updated as the main storage on the server fills with fresh information.
Such an architecture of database systems is most typical for networks to which a small number of users are connected. For its implementation, it is typical to use personal DBMS (for example, Paradox, DBase). The disadvantage of the architecture is the critically low system performance while multiple users access the same data at the same time.
DB "client-server"
It also assumes the presence of a machine in the network, which will be the main one. However, the client-server database architecture has its own peculiarity. The host computer not only stores a centralized database, but also provides the bulk of the processing of the data required by the user.
Technology divides the system into two parts: server and client. The latter will provide an interactive service, while the server one will provide information sharing, data management, security and administration.
What does client-server database architecture imply? The client application here draws up and sends a request to the remote computer server, where the centralized information storage is located. It (query) is compiled in a special SQL language - the standard access to the server when using relational databases.
After receiving the request, the remote server redirects it to the SQL server. This is the name of the program responsible for managing the remote database. It ensures the fulfillment of the request, provides the client with the required results on it.
Thus, all request processing here will take place on a remote server. To implement such an architecture, it is necessary to use multi-level DBMS. Their second name is industrial. Such DBMSs are able to organize a large-scale information system consisting of a large number of users.
Three levels of database architecture
Database architecture is divided into three main levels - three degrees of description of database elements:
- External. At this level, information is perceived by users.
- Interior. At this level, information is perceived by operating systems, DBMS (database management systems).
- Conceptual. Here, the external level of the architecture of the database system is mapped to the internal, ensuring their necessary independence from each other.
We invite the reader to become more familiar with each of the degrees presented above.
External level
The external level of architecture of database systems is the provision of information from the perspective of human users.
What follows from this? The level describes the user part of the databases (related to each user). In turn, it will consist of several external representations of information storages, databases.
Which is convenient, each user here deals in this way with the "real world", which is most adapted for him. The external representation will contain in itself only those entities, connections and attributes that are interesting and useful to a particular "user".
You should not assume that attributes, entities and relationships unnecessary for the user do not exist in the database. They are, but the "user" is most often unaware of their existence.
If we turn to the terminology of ANSI / SPARC (American National Standards Institute), the presentation of each individual user will be called external. It will include the contents of the database - such as what a specific "user" sees it. Each such external representation is determined by an external system. It also consists of defining a record of each type present in the external representation.
Concept level
We continue to analyze the architecture of the server and databases. Its next level is conceptual. It includes a generalized view of the information repository. Will describe exactly what information is stored in the database, as well as what are the relationships that unite them.
From the point of view of the administrator, the repository contains the logical structure of the database. This level of database architecture is actually a complete presentation of information requirements from the side of the company, the enterprise, which will not depend on any considerations regarding the method, methodology of its (information) storage.
Conceptual level elements
We list the components presented at the conceptual level of architecture:
- The totality of entities, their attributes, the relationships between them.
- Limitations that may be imposed on data.
- Semantic information about information in the database (related to their meaning and meaning).
- Information on measures to ensure the security of data storage, general support for their integrity.
The conceptual level is designed to support each of the external representations. Any information accessible to the user from the database should be contained (or can be calculated) at this level. However, it should be remembered that information about the methods of storing data in the system is not stored here.
Inner level
And the last step in the three-tier database architecture. Here is the physical representation in the database computer. What does it mean? The level is intended to describe the physical implementation of the database. In addition, with its help optimal performance is achieved, the economical use of the disk space of a computer system is ensured.
It contains a description of data structures, the organization of specific files that are used to implement the storage of information on disk spaces, storage devices. Here, at the internal level, the DBMS interacts with methods, access methods of operating systems, auxiliary functionality for storing and retrieving information records. The goal of all of the above: to place information on storage devices, extract data, create indexes, and so on.
Below this will be the physical level. It is already controlled by the operating system, but still under the control of the DBMS.
Elements of the inner level
The internal level of the application architecture, the database stores the following information:
- On the allocation of disk space to save indexes and information.
- A detailed description of the saving of the record (where the actual volumes of the stored data are indicated).
- Information about posting records.
- Information about data compression, selected encryption methods.
You got acquainted with common types, types of architectures of database systems. We also presented the DBMS architecture levels - external, internal and conceptual, their characteristics and elements.