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- Benjamin Day Consulting, Inc.
- Benjamin Day Consulting, Inc.

... • Properties control access to columns on the DataRow  Facilitates more complex validation ...
Conceptual modelling methods for biological data
Conceptual modelling methods for biological data

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Blueprint for DoitYourself Metadata
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... • The presence of null complicates many issues. E.g.: – Special operators needed to check if value is/is not null. – Is rating>8 true or false when rating is equal to null? What about AND, OR and NOT connectives? – We need a 3-valued logic (true, false and unknown). – Meaning of constructs must be d ...
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Relational model



The relational model for database management is an approach to managing data using a structure and language consistent with first-order predicate logic, first described in 1969 by Edgar F. Codd. In the relational model of a database, all data is represented in terms of tuples, grouped into relations. A database organized in terms of the relational model is a relational database.The purpose of the relational model is to provide a declarative method for specifying data and queries: users directly state what information the database contains and what information they want from it, and let the database management system software take care of describing data structures for storing the data and retrieval procedures for answering queries.Most relational databases use the SQL data definition and query language; these systems implement what can be regarded as an engineering approximation to the relational model. A table in an SQL database schema corresponds to a predicate variable; the contents of a table to a relation; key constraints, other constraints, and SQL queries correspond to predicates. However, SQL databases deviate from the relational model in many details, and Codd fiercely argued against deviations that compromise the original principles.
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