Examples include employee numbers, social security numbers, etc. Primary keys are unique identifiers of the relation in question. Informal Terms Formal Terms Table Relation Column Attribute/Domain Row Tuple Values in a column Domain Table Definition Schema of a Relation Populated Table Extensionġ0 Key Fields Keys are special fields that serve two main purposes: Relations (tables) correspond with entity types and with many-to-many relationship types Rows correspond with entity instances and with many- to-many relationship instances Columns correspond with attributes NOTE: The word relation (in relational database) is NOT the same as the word relationship (in E-R model)Ĩ DEFINITION SUMMARY Informal Terms Formal Terms Table Relation Column Columns in a table are also called attributes of the relation.Ħ NOTE: all relations are in 1st Normal formĭefinition: A relation is a named, two-dimensional table of data Table consists of rows (records) and columns (attribute or field) Requirements for a table to qualify as a relation: It must have a unique name Every attribute value must be atomic (not multi-valued, not composite) Every row/tuple must be unique (can’t have two rows with exactly the same values for all their fields) Attributes (columns) in tables must have unique names The order of the columns must be irrelevant The order of the rows must be irrelevant NOTE: all relations are in 1st Normal form A relation may be regarded as a set of tuples (rows).

is a tuple belonging to the CUSTOMER relation.

Each row in the CUSTOMER table may be referred to as a tuple in the table and would consist of four values. FORMAL DEFINITIONS A tuple is an ordered set of values Each value is derived from an appropriate domain. For example, the domain of Cust-id is 6 digit numbers.ĥ FORMAL DEFINITIONS A tuple is an ordered set of values 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. An) Relation schema R is defined over attributes A1, A2. FORMAL DEFINITIONS A Relation may be defined in multiple ways. Each column typically is called by its column name or column header or attribute name.Ĥ FORMAL DEFINITIONS A Relation may be defined in multiple ways. Sometimes row-ids or sequential numbers are assigned to identify the rows in the table.

Each row has a value of an item or set of items that uniquely identifies that row in the table. Each row represents a fact that corresponds to a real-world entity or relationship. A relation may alternately be though of as a set of columns. Relation is NOT same as Relationship INFORMAL DEFINITIONS RELATION: A table of values A relation may be thought of as a set of rows. State two properties of candidate keys Define first, second, and third normal form Describe problems from merging relations Transform E-R and EER diagrams to relations Create tables with entity and relational integrity constraints Use normalization to convert anomalous tables to well-structured relations McFadden By: Aatif Kamal Dated: March 2008Ģ Objectives Definition of terms List five properties of relations Modern Database Management 8th Edition Jeffrey A. 1 Chapter 5: Logical Database Design and the Relational Model

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