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Models of databases
Conceptual model
look at the data as
whole, the most stable model, it should
be the basis on which to build
processing of data
Internal model, low-level
-
it describes
way to store data in computer memory
and presents formats of records or
paths, such models are the addressing methods
, chain and
ring structures
Hierarchical model
The model includes two data structures
- types of records
- relations parent - child
Every element known as a record can
participate as a child at only one combination of records
and in the role of parent
in any number of links
Child record can not exist without the parent record
The market operation is a record
Network model
The model includes two data structures
- Types of records
- Types of collections
Each record can simultaneously takes part in many combinations of records
relationship results in many.
Such record may simultaneously and repeatedly
experiences as a parent and as a
child.
Combinations are made by special records named as clamp
The market operation is a record
Object model
There is no specified definition of object-oriented databases
The model is based on concepts such as:
- Class
- Object
- Generalization
- Abstraction
- Inheritance
Objects have methods
Semantic model
Similar to the object model
focuses on the abstraction of structure, rather than on
abstraction of action
Deductive model
Based on formal logic
Elements which are used :
- predicates
- Arguments
Predicates and arguments make up asertion
(sentence), which can take the value of the
"true" or "false"
It is often based on Datalog language.
Post-relational model
Relational model extended to object-orientated elements.
There are no strict definition - for databases performing
post-relational model there are implementations
which "are no longer relational,
but yet they are not object-oriented "
Relational model
The basis of this model has become a work published
by E.F. Codd in 1970.
In this paper, "Relational logical model for large data banks"
Codd presented the assumptions of relational
database model.
In 1990 Codd published the article "Relational model of
database management: version 2 ", extending
previous work
RMD is based on the algebra of relations
The basic elements of the model are:
- Relations
- Ties
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