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McMaster University
Computer Science

Introduction to Database Concepts 1.1 11/7/2012 4:08:00 PM • Organizing Data • entity- person, object, or event • attributes- characteristics value relationship model  each entity is a relation • each entity’s attribute has a set of fields • each column in a datasheet must have the same data type relation-table tuple-row attribute-column Field: is a single characteristic or attribute of a person place, object, event, or idea Table: is collection of fields that describe a person, place, object, event, or idea Field Values: a specific value, or content, of a field Record: set of field values Database: a collection of related tables (relational database) Common Field: connecting the records in separate table through a common field that appears in both tables Primary Key: is a field or a collection of fields whose values uniquely identify each record in a table  no two records can contain the same primary key Foreign Key: when you include a primary key from one table as a field in a second table to form a relationship between the tables Relational Database Management Systems • to manage its database, a company purchases a database management systems • a Database Management System (DBMS): is a software program that lets you create databases and then manipulate data in them • most database’s today are called relational database management systems: data is organized as a collection of tables • ability if a relation data base system is fully relational:  follow CODD’s 12 rules data is represented as tables to be relational the constraints have to represented in tables access is NOT fully relational • a company would benefit from a relational DBMS because it allows users working in different groups to share the same data • more than one user can enter data into a database • more than one user can retrieve and analyze data that others enter Databases and Relationships • a group of related tables is properly known as a relational database; Access uses “database” • You can connect the records in the separate tables through a common field ( also known as a joint field) • when you include the primary key from one table as a field in a second table, to form a relationship between the two tables, the field is called a foreign key with respect to its use in the second table • Data Dictionary: Design documentation that describes all pertinent information about the database definitions (tables, fields, data-types, constraints, relationships, keys, etc.) • Keys: Keys involving more than one field are referred to as composite, concatenated or compound keys • to vopy records the table has to have the same structure, same fields, design, order, characterists Restrictions on Keys: • PK must have unique values; no duplicates allowed • PK must not have a null value; a data value is required • For each non-null FK value, a corresponding PK value must exist elsewhere (i.e., in another table in the database) Types of relationships among tables: • One to One (1:1) • One to Many (1:N) • Many to Many (N:M) • Examples: • 1:1 … Husband/Wife • 1:N … Parent/Child; Account/Transaction • M:N … Doctor/Patient Creating a Database • backstage view provides options for you to get information about the current database, create a new one, or open an existing one • a template is a predesigned database that includes professionally desgined tables, reports and other database objects Creating a Table in Datasheet View • tables contains all the data in a databse and are the fundamental objects for your work • Click the Create tab on the Ribbon • In the Tables group, click the Table button. • Accept the default ID primary key field with the AutoNumber data-type, or rename the field and change its data-type, if necessary • Generally wise to avoid using AutoNumber data-type for PK; also avoid accepting Access suggestions for default PK (i.e., explicitly choose your own) • In the Add & Delete group on the Fields tab, click the button for the type of field you want to add to the table (for example, click the Text button), and then type the field name. Repeat this step to add all the necessary fields to the table • In the first row below the field names, enter the value for each field in the first record, pressing the tab or Enter key to move to the next field • After entering the value for the last field in the first record, press the Tab or Enter key to move to the next
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