Session3-b

Session3-b - Elmasri/Navathe, Fundamentals of Database...

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Unformatted text preview: Elmasri/Navathe, Fundamentals of Database Systems, Fifth Edition Elmasri/Navathe, Fundamentals of Database Systems, Fifth Edition The Relational Data Model and Relational Database Constraints 2 Elmasri/Navathe, Fundamentals of Database Systems, Fifth Edition Elmasri/Navathe, Fundamentals of Database Systems, Fifth Edition Chapter Outline Relational Model Concepts Relational Model Constraints and Relational Database Schemas Update Operations and Dealing with Constraint Violations 3 Elmasri/Navathe, Fundamentals of Database Systems, Fifth Edition Elmasri/Navathe, Fundamentals of Database Systems, Fifth Edition Relational Model Concepts The relational Model of Data is based on the concept of a Relation. The model was first proposed by Dr. T.F. Codd of IBM in 1970 in the following paper: "A Relational Model for Large Shared Data Banks," Communications of the ACM, June 1970. The above paper caused a major revolution in the field of Database management and earned Ted Codd the coveted ACM Turing Award. 4 Elmasri/Navathe, Fundamentals of Database Systems, Fifth Edition Elmasri/Navathe, Fundamentals of Database Systems, Fifth Edition Informal Definitions RELATION: A table of values A relation may be thought of as a set of rows . Each row represents a fact that corresponds to a real-world entity or relationship . Each row has a value of an item or set of items that uniquely identifies that row in the table. Each column typically is called by its column name or column header or attribute name. 5 Elmasri/Navathe, Fundamentals of Database Systems, Fifth Edition Elmasri/Navathe, Fundamentals of Database Systems, Fifth Edition Informal Definitions Key of a Relation: Each row has a value of a data item (or set of items) that uniquely identifies that row in the table Called the key In the STUDENT table, SSN is the key Sometimes row-ids or sequential numbers are assigned as keys to identify the rows in a table Called artificial key or surrogate key 6 Elmasri/Navathe, Fundamentals of Database Systems, Fifth Edition Elmasri/Navathe, Fundamentals of Database Systems, Fifth Edition Example - Figure 5.1 7 Elmasri/Navathe, Fundamentals of Database Systems, Fifth Edition Elmasri/Navathe, Fundamentals of Database Systems, Fifth Edition Formal definitions The Schema (or description) of a Relation: Denoted by R(A1, A2, .....An) R is the name of the relation The attributes of the relation are A1, A2, ..., An Example: CUSTOMER (Cust-id, Cust-name, Address, Phone#) CUSTOMER is the relation name Defined over the four attributes: Cust-id, Cust-name, Address, Phone# Each attribute has a domain or a set of valid values....
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Session3-b - Elmasri/Navathe, Fundamentals of Database...

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