A database is an abbreviation that stands for "database" or "database" (depending on context). In this article, we consider what she / they are, what they are and where they are used. We also discuss whether DBMS and DB are the same or not.
Terminology
A database is called a structured repository of information. A database is also an
information model that can accommodate certain data, provided that they are necessarily ordered. Each of us worked with the database at least once, but we could not even guess about it, for example, entering a search query, we turn to a large-scale database for specific information.
DBMS is another abbreviation, which stands for "database management system." In a general sense, they represent various software solutions with which you can organize database data. This refers to filling the database with information, organizing it, deleting, copying, analyzing and much more.
Types of DB
In database theory, several types are distinguished. There are:
- Relational databases (from the English word relation, which translates as “relationship”) - are characterized by relationships and are expressed in the aggregate of interrelated entities. The latter are presented in the form of plates that contain database data. This is the most common type of database.
- Hierarchical - relations at the level of "ancestor-descendant", "boss-subordinate."
- Network - a branch from the previous view.
- Object-oriented, which work directly with the appropriate programming methodology (OOP).
Let us consider each of them in more detail, simultaneously dwelling on the basic ideas and concepts of the database.
Is a DB a plate?
Relational databases in their usual representation do not cause difficulties for understanding - these are signs with information. For clarification, you can call for help a 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 former contains directly information, data, and the latter contains descriptions of what the records mean. For example, the field is "name", the entry is "Katerina."
Value fields are set for fields. They can be numeric, symbolic, date, time, etc. In addition, each table should have a key field - records in it uniquely identify 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.
Relationships Between Tables
To provide links between tables in the DBMS there are data schemes. Connections are:
- One-to-one - each record in the table corresponds to only one record from another plate.
- One-to-many and many-to-many. Several records from a linked table can correspond to one record at once. And vice versa (for the second option).
- Many-to-many. It is easy to guess that in this case for several rows several rows of another table can be selected for communication (such a relationship is organized using an intermediate table and two relationships of the above type).
Move up and down
Hierarchical databases have a much clearer structure than relational ones. They are subject to strict submission. There is a root element - the "top", from which 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.
This type is conveniently used to build repositories of information of an already ordered structure: for example, the database of a military unit or file manager. A disadvantage is the impossibility for a node to have more than one ancestor, as well as the complexity of the database logic.
Expanding Communication
Network databases have become a solution to the lack of hierarchical, named just above. The only difference between this type and the previous one was the many-to-many relationship, which in this case manifests itself in the fact that as an ancestor can have many heirs, so they, descendants, can come from several nodes at once.
Tabular display method
Despite the fact that tables are primarily associated with relational databases, hierarchical and network databases can also be represented in the form of tables. The main difference between these types is precisely in the principle of constructing the structure: relational, in comparison with the other two, are much more free and less ordered.
Object oriented type
The last type under consideration - object-oriented - is the least common. All because he is very highly specialized. The complex data structures of such a database form an object and work directly with object-oriented programming languages. They were developed in the eighties of the last century and have not yet received much popularity because of their complexity and not very high performance rate.