Restructuring hierarchical database objects
Theoretical Computer Science - First International Conference on Database Theory, Rome, September 1986
The structure of the relational database model
The structure of the relational database model
The characterization of branching dependencies
Discrete Applied Mathematics - Special issue on combinatorial problems in databases
Horn clauses and database dependencies
Journal of the ACM (JACM)
Data on the Web: from relations to semistructured data and XML
Data on the Web: from relations to semistructured data and XML
Foundations of Databases: The Logical Level
Foundations of Databases: The Logical Level
Entity-Relationship Modeling: Foundations of Database Technology
Entity-Relationship Modeling: Foundations of Database Technology
Extremal Combinatorial Problems in Relational Data Base
FCT '81 Proceedings of the 1981 International FCT-Conference on Fundamentals of Computation Theory
Axiomatizing functional dependencies in the higher-order entity-relationship model
Information Processing Letters
Functional dependencies over XML documents with DTDs
Acta Cybernetica
Counter-free keys and functional dependencies in higher-order datamodels
Fundamenta Informaticae
Axiomatisations of functional dependencies in the presence of records, lists, sets and multisets
Theoretical Computer Science - Logic, language, information and computation
On the existence of armstrong instances with bounded domains
FoIKS'08 Proceedings of the 5th international conference on Foundations of information and knowledge systems
Coding theory motivated by relational databases
SDKB'10 Proceedings of the 4th international conference on Semantics in data and knowledge bases
On the existence of armstrong data trees for XML functional dependencies
FoIKS'10 Proceedings of the 6th international conference on Foundations of Information and Knowledge Systems
FoIKS'12 Proceedings of the 7th international conference on Foundations of Information and Knowledge Systems
Note on the size of binary Armstrong codes
Designs, Codes and Cryptography
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The definition of keys, antikeys, Armstrong-instances are extended to complex values in the presence of several constructors. These include tuple, list, set and a union constructor. Nested data structures are built using the various constructors in a tree-like fashion. The union constructor complicates all results and proofs significantly. The reason for this is that it comes along with non-trivial restructuring rules. Also, so-called counter attributes need to be introduced. It is shown that keys can be identified with closed sets of subattributes under a certain closure operator. Minimal keys correspond to closed sets minimal under set-wise containment. The existence of Armstrong databases for given minimal key systems is investigated. A sufficient condition is given and some necessary conditions are also exhibited. Weak keys can be obtained if functional dependency is replaced by weak functional dependency in the definition. It is shown, that this leads to the same concept. Strong keys are defined as principal ideals in the subattribute lattice. Characterization of antikeys for strong keys is given. Some numerical necessary conditions for the existence of Armstrong databases in case of degenerate keys are shown. This leads to the theory of bounded domain attributes. The complexity of the problem is shown through several examples.