TAILIEUCHUNG - The Relational Data Model and Relational Database Constraints

The relational Model of Data is based on the concept of a Relation. A Relation is a mathematical concept based on the ideas of sets. The strength of the relational approach to data management comes from the formal foundation provided by the theory of relations. We review the essentials of the relational approach in this chapter. | The Relational Data Model and Relational Database Constraints Chapter Outline Relational Model Concepts Relational Model Constraints and Relational Database Schemas Update Operations and Dealing with Constraint Violations Relational Model Concepts The relational Model of Data is based on the concept of a Relation. A Relation is a mathematical concept based on the ideas of sets. The strength of the relational approach to data management comes from the formal foundation provided by the theory of relations. We review the essentials of the relational approach in this chapter. Relational Model Concepts The model was first proposed by Dr. . 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. INFORMAL DEFINITIONS RELATION: A table of values A relation may be thought of as a set of rows. A relation may alternately be though of as a set of columns. 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. Sometimes row-ids or sequential numbers are assigned to identify the rows in the table. Each column typically is called by its column name or column header or attribute name. FORMAL DEFINITIONS A Relation may be defined in multiple ways. The Schema of a Relation: R (A1, A2, .An) Relation schema R is defined over attributes A1, A2, .An For Example - CUSTOMER (Cust-id, Cust-name, Address, Phone#) Here, CUSTOMER is a relation defined over the four attributes Cust-id, Cust-name, Address, Phone#, each of which has a domain or a set of valid values. For example, the domain of Cust-id is 6 digit numbers. FORMAL DEFINITIONS A tuple is an ordered set of values Each value is derived from an appropriate domain. Each row in the CUSTOMER table may .

• Cơ sở dữ liệu
• Update Operations
• Constraint Violations
• relational Model
• INFORMAL DEFINITIONS
• Referential Integrity
• relation instance
• Database Systems
• Relational Data Model
• ER EER to Relational Mapping
• Relational Integrity Constraints
• Update Operations on Relations
• Main Phases of Database Design
• Instance Splitting Strategies
• Dependency Relation based
• Information Extraction
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• mô hình ngôn ngữ
• xử lý ngôn ngữ tự nhiên