In the classical theory of databases, the data model is a formal theory of the presentation and processing of data in a database management system (DBMS), which includes at least three aspects:
- aspect of the structure : methods for describing the types and logical structures of data in a database ;
- Manipulation aspect : data manipulation methods;
- integrity aspect : methods for describing and maintaining database integrity .
The aspect of the structure determines what the database is logically, the aspect of manipulation determines how to transition between the states of the database (that is, how to modify data) and how to extract data from the database, the integrity aspect determines the means of describing the correct states of the database.
A data model is an abstract, self-sufficient, logical definition of objects, operators, and other elements that together constitute an abstract data access machine with which the user interacts. These objects allow you to simulate the data structure, and operators - data behavior [1] .
Each database and DBMS is built on the basis of some explicit or implicit data model. All DBMSs built on the same data model are of the same type. For example, the basis of a relational DBMS is a relational data model , network DBMS - a network data model , hierarchical DBMS - a hierarchical data model , etc.
About Terminology
In literature, articles, and in everyday speech, the term “data model” is sometimes used in the sense of “ database schema ” (“ database model ”). Such use is incorrect, as many authoritative experts point out, including K.J.Date , M.R. Kogalovsky, S.D. Kuznetsov. A data model is a theory , or a modeling tool , while a database model (database schema) is the result of a simulation . According to K. Data, the relationship between these concepts is similar to the relationship between a programming language and a specific program in this language [1] .
M.R. Kogalovsky explains the evolution of the meaning of the term as follows. Initially, the concept of a data model was used as a synonym for the data structure in a particular database . In the process of developing the theory of database systems, the term "data model" has acquired new content. There was a need for a term that would designate a tool, and not the result of modeling, and would thus embody a variety of all kinds of databases of a certain class. In the second half of the 1970s, in many publications devoted to these problems, the same term “data model” began to be used for these purposes. Currently, in the scientific literature, the term “data model” is interpreted in the vast majority of cases in the instrumental sense (as a modeling tool) [2] .
However, for a long time the term “data model” was used without a formal definition. One of the first specialists who quite formally defined this concept was E. Codd . In the article “Data Models in Database Management” [3], he defined the data model as a combination of three components:
- collections of types of data objects that form the basic building blocks for any database corresponding to the model;
- collections of general integrity rules that limit the set of instances of those types of objects that may legally appear in any such database;
- collections of operations applicable to such instances of objects for sampling and other purposes [4] .
See also
- Ontology (computer science)
Notes
- ↑ 1 2 Date C. J. Introduction to Database Systems. - 8th ed. - M .: "Williams", 2006.
- ↑ M.R. Kogalovsky. Abstractions and models in database systems (inaccessible link) . Date of treatment March 2, 2010. Archived June 13, 2008.
- ↑ Codd, EF "Data Models in Database Management. Proc. Workshop in Data Abstraction, Databases, and Conceptual Modeling (Michael L. Brodie and Stephen N. Zilles, eds.), Pingree Park, Colo. (June 1980): ACM SIGART Newsletter No. 74 (January 1981); ACM SIGMOD Record 11 (2), February 1981; ACM SIGPLAN Notices 16 (1), January 1981
- ↑ Date K. J. The relational model will stand the test of time // Intelligent Enterprise, June 1, 1999, Volume 2, Number 8)
Literature
- Date C. J. Introduction to Database Systems = Introduction to Database Systems. - 8th ed. - M .: "Williams" , 2006. - 1328 p. - ISBN 0-321-19784-4 .
- Kogalovsky M.R. Perspective technologies of information systems. - M .: DMK Press; IT Co., 2003. - 288 p. - ISBN 5-279-02276-4 .
- Kogalovsky M.R. Encyclopedia of Database Technologies. - M .: Finance and statistics , 2002. - 800 p. - ISBN 5-279-02276-4 .
- Tsikritzis D., Lochowski F. Data models = D. Tsichritzis, F. Lochovsky. Data Models. Prentice Hall, 1982. - M .: Finance and Statistics , 1985 .-- 344 p.