DB is ... Types and properties of the database

The database is an abbreviation, which stands for "database", or "database" (depending on the context). In this article, we will consider what it / they are, what they are and where they are applied. Also we will discuss DBMS and DB - this is the same or not.

Terminology

A database is a kind of structured information store. The database is also an information model capable of containing certain data, with the proviso that they will necessarily be ordered. Each of us worked with the DB at least once, but could not even guess about it, for example, when entering a search query, we turn to a large-scale database for specific information.

DBMS is another abbreviation, which is deciphered as a "database management system". In general, they represent various software solutions with which you can organize database data. This means filling the database with information, organizing it, deleting it, copying it, analyzing it, and so on.

Types of databases

In the theory of databases, several of their types are distinguished. There are:

• Relational databases (from the English word relation, which translates as "communication") - characterized by relationships and expressed in a set of interrelated entities. The latter are presented in the form of tablets, which contain the data of the database. This is the most common type of database.
• Hierarchical - connections at the level of "ancestor-descendant," "boss-subordinate."
• Network - a branch from the previous view.
• Object-oriented, which directly work with the corresponding programming methodology (OOP).

Let's consider each of them in more detail, simultaneously stopping at the basic ideas and concepts of the database.

DB - is it a sign?

Relational databases in their usual representation do not cause difficulties for understanding - these are information boards. For clarification, you can call for help very well-known DBMS from Microsoft - "Access", which is part of their usual office suite of applications.

Relational database tables have records (rows) and fields (columns). The first contains directly information, data, in the latter - a description of what exactly records mean. For example, the field is "name", the entry is "Katerina".

Value types are defined for fields. They can be numeric, symbolic, date, time, etc. In addition, each table should have a key field - entries in it uniquely identify the data.

It should be understood that the database itself is not a table. The database can store from one to several hundred tables, depending on the amount and variety of information.

Links between tables

To provide links between tables in the DBMS, there are data schemes. There are connections:

• "One-to-one" - only one entry from another table corresponds to each entry in the table.
• "One-to-many" and "many-to-many". A single record can correspond to several of the associated tables at once. And vice versa (for the second option).
• "Many-to-many." It is already easy to guess that in this case several rows of another table can be chosen for several rows for communication (this connection is organized using an intermediate table and two links of the above type).

Move up and down

Hierarchical databases have a much more precise structure than relational ones. They are characterized by strict subordination. There is a root element - the "top", from which the subordinates branch out - "heirs" or "descendants". A hierarchical database is a database with a tree structure, in which each node can have only one ancestor.

It is convenient to use this type for building information stores of an already ordered structure: for example, a database of a military unit or a file manager. The disadvantage is the impossibility for a node to have more than one ancestor, as well as the complexity of the logic of the database.

Extend the links

Network DBs are the solution to the lack of hierarchical, named just above. The only difference of this type from the previous one was the connection "many-to-many", which in this case is manifested in the fact that as ancestor can have many heirs, so they, descendants, can occur from several nodes at once.

Tabular mode of display

Despite the fact that tables are associated primarily with relational databases, both hierarchical and network tables can also be represented in the form of tables. The main difference between these types is precisely the construction of the structure: the relational ones, in comparison with the other two, are much more free and less ordered.

Object-oriented type

The last considered type - object-oriented - is the least common. All because he is very narrowly specialized. Complex data structures of such a database form an object and work directly with the languages of object-oriented programming. They were developed in the eighties of the last century and have not received much popularity yet because of their complexity and not very high speed.