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. |02.04 - Conceptual Model .
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Conceptual model abstraction pattern basis for
Relation Database Structure manipulation is the
original idea of elements organized by it's purpose.
The main author in this field is E. F. Codd.
When he published his article on relation model
implementation using mathematical apparatus he was
employed in the IBM research laboratory.
He was looking for method how to separate user from
the data organization likewise deductive programs
already allowed that. He defined requirement to
keep the work sequence even when the database
inner structure is changed. Like this he enabled
to separate the user's work sequence for database
structure manipulation from the inner organization of
data base.
Codd's presumption was the dynamical variability
of inner organization as result of frequent data
updates, output reports modifications and natural
growth of the information stored in the database.
By separation of the user's data processing from
the inner machine data representation and inner
mechanisms Codd achieved the preservation of the work
sequences with the data base.
The separation of information structure from the
user's interface was implemented in the form of query
language. Query language didn't have consider the
order of each elements in the data structure on the
physical level of database. He introduced principles
allowing faster access to the bigger amount of data
and he specified the method of abstraction for the
data access.
He did also engage in the future direction of
query language development. As the base functional
apparatus for the query language he used predicate
calculus. That brought him to the idea to connect
argument with the stored language even in the case
when relation is not know but exists. He defined
as the base query language property it's ability
to be encapsulated in different host languages.
The basic principle of data language principle
became it's description ability. That brought it's
characteristics in the term of ability not only to
formulate data structure, but by the same language
constructs manipulate with the data structure.
Data Model is connected to the data structure,
operations and operations constraint. One of it's
classification is based on the level of abstraction.
Two main levels of abstractions are logical and
conceptual. On the logical level it's the user's
logical structure knowledge, primary and foreign
keys existence. There are constraints for the data
reorganizations and data structure.
On the logical layer there is an Entity
Relationship model and logical data structure as are
keys, foreign keys, constraints and entities joins.
On the conceptual level there is ER model that's
widely used for conceptual modeling.
