CP363 Lecture Notes - Lecture 6: Relational Database, Relational Model, Hard Disk Drive
8 Apr 2019
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Document Summary
The relational data model and relational database constraints. The relational model of data is based on the concept of relation. A relation is a mathematical concept based on the ideas of sets. The model was first proposed by dr. e. f codd of ibm research in 1970 in the following paper. A relational model for large shared data banks . Relation looks like a table of values. A relation typically contains a set of rows. The data elements in each row represent certain facts that correspond to a real world entity or relationship. In a formal model rows are called tuples. Attributes must have the same data type. Each column has a column header that gives an indication of the meaning of the data item. Table : 7 attributes (columns), 5 tuples (5 rows) represent 5 students. Nontrivial problem- how to deal with null values.
