Since the concept of data is not strictly defined in the article “DB and DBMS”, we will agree on the terminology used (note that this article, in turn, refers to the dictionary of school informatics). We will require data to be atomic, i.e. indivisible. Any collection of such indivisible data is already a structure. Of course, here we also have to agree on when to stop in the desire and opportunity to “share” something. With the 먹튀검증 this is important.
For example, a string can be divided into characters, in this sense the string is certainly a data structure. But if you agree not to divide the string into characters, then you can consider it atomic. The relevant terms are inextricably linked with the essential concept of “data type”.
The Right Properties
When talking about the properties of an entity (object), they explicitly or implicitly mean that each specific property (in the table the recording field) takes values from a certain set. The specified set is called a data type.
The Right Programming
In programming, the terms “simple” and “complex” (“composite”) data types are often used. In the above sense, data types are only simple, and complex types are already data structures. Although this is only a matter of terminology, with respect to relational databases it is convenient to adhere to the described system of concepts. You can read more about data types and structures in the corresponding articles. In particular, these articles focus on the fact that the type determines the many operations that can be performed on data.
All relational DBMSs support data of the following main types:
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The list is not exhaustive. As a rule, DBMSs also have types for storing large text and binary data, special “money” types, etc. The following figure, a screenshot of the Microsoft Access table designer, shows the types supported by this system.
We also note that, as a rule, types can be equipped with modifiers that refine the corresponding data set (range of values). For example, in Microsoft Access, data of a numeric type can simply be “integer”, “long integer”, “real”, etc.
- The border between type and type with a modifier is more convenient to draw in the framework of a specific DBMS. It is usually considered that the data for the description of which one keyword is used in the SQL language belongs to the same type, and those that are described in different words are different.
Recall that the relational model prescribes organizing data into tables, the set of which the developer determines at the stage of converting the infological model of the subject domain into the datalogical one. At the same stage, the properties of entities become fields of the corresponding types, primary keys are determined, and relationships between tables are established. The relevant concepts are discussed in detail in this article.