Department «digital economy and information technology» subject "database"

BASIC DATA MODELS
Record–named collection of data elements or data elements and aggregates. A record is an aggregate that is not part of any other aggregate; it can have a complex hierarchical structure because aggregation can be applied multiple times. A distinction is made between a record type (its structure) and a record instance, i.e. a record with specific data element values. One record describes the properties of one software entity (instance). Sometimes the term "record" is replaced by the term "group".
Example records type EMPLOYEE
Operations on data
The data model defines a set of actions that can be performed on a certain database implementation to transfer it from one state to another. This set is correlated with the data manipulation language (Data Manipulation Language,DML).
Any operation on data includes data selection (select), that is, the selection from the entire set of exactly those data on which the required operation must be performed, and the action on the selected data, which determines the nature of the operation. A selection condition is a certain criterion for selecting data, in which the logical position of a data element, its value and connections between data can be used.
Based on the type of actions performed, the following operations are distinguished:-identification of data and finding their position in the database;-sampling (reading) data from the database;-inclusion (recording) of data in the database;-deleting data from the database;-modification (change) of database data.
Integrity Constraints
Integrity Constraintsare rules that the values ​​of data elements must satisfy. Integrity constraints are divided into explicit and implicit.
Implicitthe limitations are determined by the data structure itself. For example, the fact that a record of typeEMPLOYEEhas a fieldDate of Birth, essentially serves as an integrity constraint, meaning thatEach employee of the organization has a date of birth, and only one.
Explicitconstraints are included in the database structure using data control language tools (DCL,Data Control Language). Explicit constraints are most often conditions imposed on data values.For example, the passport number is unique, the salary cannot be negative, and the employee’s hiring date will necessarily be less than the date of his transfer to another job.