Incomplete Information in Relational Databases
Journal of the ACM (JACM)
Notions of dependency satisfaction
Journal of the ACM (JACM) - The MIT Press scientific computation series
The relational model with relation-valued attributes
Information Systems
Non first normal form relations: An algebra allowing data restructuring
Journal of Computer and System Sciences
The Verso algebra or how to answer queries with fewer joins
Journal of Computer and System Sciences
Multilevel nested relational structures
Journal of Computer and System Sciences
Updating databases in the weak instance model
PODS '89 Proceedings of the eighth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems
A new interpretation for Null values in the weak instance model
Journal of Computer and System Sciences
Using powerdomains to generalize relational databases
Theoretical Computer Science
Semantics for null extended nested relations
ACM Transactions on Database Systems (TODS)
Database states and their tableaux
ACM Transactions on Database Systems (TODS)
On the foundations of the universal relation model
ACM Transactions on Database Systems (TODS)
A simplied universal relation assumption and its properties
ACM Transactions on Database Systems (TODS)
A characterization of globally consistent databases and their correct access paths
ACM Transactions on Database Systems (TODS)
Extending the database relational model to capture more meaning
ACM Transactions on Database Systems (TODS)
Testing implications of data dependencies
ACM Transactions on Database Systems (TODS)
On the Equivalence of Database Models
Journal of the ACM (JACM)
Testing satisfaction of functional dependencies
Journal of the ACM (JACM)
Degrees of acyclicity for hypergraphs and relational database schemes
Journal of the ACM (JACM)
Relaxing the universal relation scheme assumption
PODS '85 Proceedings of the fourth ACM SIGACT-SIGMOD symposium on Principles of database systems
Design and development of data-intensive web sites: The Araneus approach
ACM Transactions on Internet Technology (TOIT)
SQL query optimization through nested relational algebra
ACM Transactions on Database Systems (TODS)
On Inferences ofWeak Multivalued Dependencies
Fundamenta Informaticae
On Inferences ofWeak Multivalued Dependencies
Fundamenta Informaticae
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The nested universal relation (UR) model aims to provide logical data independence to the nested relational model by allowing users to view the database as if it were composed of a single nested relation. Moreover, non-technical users may find the nested relational model too complex to interact with, a problem we call herein the usability problem. The nested UR model solves the usability problem by allowing users to interact with the nested database without having to know its detailed structure, which may be complex. In order to formalise the nested UR model we extend the weak instance approach to the (classical) UR model to the nested weak instance approach to the nested UR model. The nested weak instance approach leads naturally to the definition of the underlying data structure for the nested UR model, namely the nested representative instance (NRI) over the nested universal relation scheme. We present two different definitions of the NRI and show that they are equivalent. First, we define the NRI declaratively as the greatest lower bound of the set of nested weak instances with respect to a natural ordering defined on nested relations. Second, we define the NRI constructively as the result of computing the extended chase on the underlying nested database. Finally, we show that the weak instance approach to the UR model is a special case of the nested weak instance approach to the nested UR model, thus allowing us to implement a flexible UR interface by using the nested UR model; this provides us with all the advantages of nested relations over flat relations.