CSC343H1 Study Guide - Final Guide: Arity, Tuple
Document Summary
Mary (m), xiao (x) ! Bookstore (b), wind (w: network (graph) data model. Employers (e) = head of linked list of employers. Students (s) = head of linked list of students: hierarchical (tree) data model. Employers (e) = parent node of employers. Double nodes needed to maintain tree: relational (table) data model. Tables may store relations between attributes. Matches how we think about data. Declarative access to data (system optimizes for you) Relationships specified by queries. Develop, maintain apps and data layout separately: relational model, logical representation of data. Two- dimensional tables (relations: formal system for manipulating relations, result: High- level (logical, declarative) description of data. Mechanical rules for rewriting/optimizing low- level access. Formal methods to reason about soundness: history: Proposed by edgar f. codd in 1970 as a data model that strongly supports data independence. Based on (a variant of) the mathematical notion of relation ! represented as tables: mathematical relations, cartesian product.
