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1
Content available Fuzzy recursive relationships in relational databases
Myszkorowski K.
Information Systems in Management
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2018
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Vol. 7, No. 1
35--46
EN
Recursive relationships are used for modelling problems coming from the real life, such as, for example, a relationship describing formal dependencies between employees of an enterprise, where creation of work groups and teams requires analysis of many elements. In conventional database systems, the precision of data is assumed. If our knowledge of the fragment of reality to be modelled is imperfect one should apply tools for describing uncertain or imprecise information. One of them is the fuzzy set theory. The paper deals with recursive relationships in fuzzy databases. The analysis is performed with the use of the theory of interval-valued fuzzy sets. A definition of a fuzzy interval recursive relationship has been presented. The paper defines different connections of entities which participate in such relationships. Operations of the extended relational algebra are also discussed.
2
Content available remote Integrity rules for multiargument relationships in possibilistic databases
Myszkorowski K.
Journal of Applied Computer Science
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2016
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Vol. 24, nr 3
21--32
EN
The paper contains an analysis of multiargument relationships in possibilistic databases. A multiargument relationship may be formally presented using the relational notation R(X1, X2,...,Xn), where R is the name of the relationship and attributes Xi denote keys of entity sets which participate in it. The dependencies between all n attributes describe the integrity constraints and must not be infringed. They constitute a restriction for relationships of fewer attributes. In the paper it is considered a possible coexistence of associations between k < n attributes of the n-ary relationship. The analysis is carried out using the theory of fuzzy functional dependencies. The notion of functional dependency has been appropriately extended according to the representation of data.
3
Content available remote Fuzzy querying with the use of interval-valued fuzzy sets
Myszkorowski K., Superson I.
Journal of Applied Computer Science
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2013
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Vol. 21, nr 1
89--105
EN
The paper deals with flexible queries in relational databases. Conditions included in queries are modeled with the use of interval-valued fuzzy sets. Each value returned by a query is associated with a subinterval of [0,1] which expresses a membership degree. The bounds of membership intervals have been determined for different operations of relational algebra and different SQL operators.
4
Fuzzy functional dependencies within the possibilistic databases framework
Myszkorowski K.
Metody Informatyki Stosowanej
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2011
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nr 4
75-86
EN
The paper deals with fuzzy functional dependencies in relational databases. For data representation a possibility-based approach has been used. It is assumed, that attribute values are represented by means of interval-valued possibility distributions. According to this approach extended definitions of fuzzy functional dependency and fuzzy normal forms have been introduced.
5
Zależności funkcyjne między atrybutami rozmytymi poziomu drugiego z interwałową funkcją przynależności
Myszkorowski K.
Studia Informatica
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2010
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Vol. 31, nr 2A
457-468
PL
Przedmiotem artykułu są zależności funkcyjne w rozmytych bazach danych. Do opisu atrybutów zostały wykorzystane interwałowe zbiory rozmyte pozimu drugiego. Zastosowano podejście posybilistyczne. Stopień rozmytej zależności funkcyjnej został określony na podstawie miar bliskości wartości atrybutów. Zależności takie podlegają rozszerzonym regułom Armstronga. Sformułowano definicje rozmytych postaci normalnych.
EN
The paper deals with functional dependencies in fuzzy databases. Attribute values are represented by means of interval-valued level-2 fuzzy sets. A possibility-based approach has been applied. The degree of a fuzzy functional dependency has been determined by means of closeness measures of attribute values. Such dependencies are submitted to extended Armstrong's axioms. Definitions of fuzzy normal forms have been formulated.
6
Interwałowe rozkłady możliwości i ich zastosowanie w rozmytych bazach danych
Myszkorowski K.
Studia Informatica
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2009
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Vol. 30, nr 2A
107-120
PL
Tematyka artykułu dotyczy modelowania niepełnej informacji w relacyjnych bazach danych za pomocą interwałowych zbiorów rozmytych typu drugiego. Zastosowano podejście posybilistyczne. Wartości atrybutów relacji są reprezentowane za pomocą interwałowych rozkładów możliwości. Przedstawiono analizę oceny stopnia spełnienia warunków stawianych zapytań. Za pomocą interwałowego rozmytego implikatora zdefiniowano pojęcie rozmytej zależności funkcyjnej między atrybutami.
EN
The paper deals with modeling of imperfect information in relational databases by means of interval-valued fuzzy sets. The possibility-based approach has been applied. Attribute values are represented by means of interval possibility distributions. The analysis of the extent to which attribute values satisfy query conditions has been presented. An interval-valued fuzzy implicator has been applied in the definition of the fuzzy functional dependency between attributes.
7
Content available remote Inheritance Anomalies in Object-Oriented Databases
Myszkorowski K., Graczyk M.
Journal of Applied Computer Science
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2005
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Vol. 13, nr 1
69-85
EN
The paper deals with object-oriented databases, with a special emphasis put on inheritance problems taking place in them. In object-oriented designing it is the question of finding a proper inheritance hierarchy that causes a serious practical difficulty. Dealing with these issues, the paper begins with presenting inheritance anomalies that may occur in a model under designing, then defines a normal inheritance form devoid of the anomalies, and finally proposes an algorithm for transforming an object-oriented database to the defined normal form.
8
Content available remote Object-oriented database design for a hospital based on nested relations
Kącki E., Myszkorowski K.
Journal of Applied Computer Science
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2002
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Vol. 10, nr 2
49-65
EN
The paper deals with applying object-oriented methodology for modeling a database of a hospital. The presented model is very general, includes all domains of hospital activity and can be extended according to the needs. The semantics of update operations is defined such that the model-inherent integrity constraints such as typing, class membership, subtype- and subclass- relationship, and class predicates can be maintained automatically.
9
Content available remote New definitions of relational operations for nested relations
Krzemiński P., Myszkorowski K.
Journal of Applied Computer Science
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1998
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Vol. 6, nr 1
5-24
EN
In this paper, extended projection and join operators for nested relations will be defined. Such relations arise by rejection of the first normal form as a standard valid for flat relations. They are characterised by occurrence of both attributes with atomic domains and complex attributes whose value is a certain subrelation. The described operators are an extension of projection and join operators of nested relations belonging to algebra as proposed in [10]. They will be defined for a wider class of relations, and they will permit to handle the nested schemas more freely. Both the operators will also act inside the relation class in their partitioned normal form.
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