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

Relational Data Model (RDM)
A relation has two main properties: - there should not be identical tuples in a relation, because it's a lot.
The order of the tuples in a relation is immaterial.
Thus, there is no first, second, or last tuple in a relation: when outputting relation data, the tuples are output in random order unless ordered by field values.
Relational Data Model (RDM)
Relational data model– this is mA data model based on representing data as a set of relations, each of which is a subset of the Cartesian product of certain sets. Data manipulation in RMD is carried out using operationsrelational algebra(RA) orrelational calculus.Relational algebra is based on set theory, and relational calculus is based on mathematical logic (or rather, first-order predicate calculus). Studying relational calculusis beyond the scope of this manual. We will consider only the operations of relational algebra.
Other data models
The increasing complexity of database applications and the limitations of the relational model led to the development of the Codd model, which was first calledextended relational model, and later received its development in the object-relational data model. Databases based on these models are usually referred to asIII-to the generation.
The object-relational data model (ORDM) is implemented using relational tables, but includes objects similar to objects in object-oriented programming. ORMD uses such object-oriented components as custom data types, encapsulation, polymorphism, inheritance, method overriding, etc.
Object-oriented data modelX
Another approach to building a database is the use of an object-oriented data model (OODM). Data modeling in OOMD is based on the concept of an object. OOMD is usually used in complex subject areas that lack the functionality of a relational model to model.
When creating object-oriented DBMS (OODBMS), different methods are used, namely: - embedding tools designed for working with databases into an object-oriented language; - expansion of the existing language for working with databases with object-oriented functions; - creation of object-oriented libraries of functions for working with databases; - creation of a new language and a new object-oriented data model.
The advantages of OOMD include broad domain modeling capabilities, an expressive query language, and high performance. Each object in the OOMD has a unique identifier (OID–object identifier). Contact byOIDis much faster than searching in a relational table.
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