Transcript Document
Chapter 5 Relationships & Queries in Databases Types of Relationships One to One Examples? Analysis Technique Consider ThingA and ThingB Can ThingA be related to more than one ThingB? Can ThingB be related to more than one ThingA? If the two answers are NO, then it is a one to one relationship. Types of Relationships One to Many Examples? Analysis Technique Consider ThingA and ThingB Can ThingA be related to more than one ThingB? Can ThingB be related to more than one ThingA? If the answers are no and yes, or yes and no, then the relationship is one to many. Types of Relationships Many to Many Examples? Analysis Technique Consider ThingA and ThingB Can ThingA be related to more than one ThingB? Can ThingB be related to more than one ThingA? If the answers are yes and yes, then you have a many to many relationship Hierarchical Leads to Serious Data Redundancy Hierarchical Network Network Difficult to manage and implement relationships Relational The most popular structure Relational Orders OID CID PID Quantity 001 508 199 500,000 002 508 201 2 003 510 201 1 Customers Products CID FName LName Address PID Description Cost 508 Eric Breimer ... 199 Viagra $45.99 509 Andrew Zych ... 200 Tooth Paste $2.58 510 Greg Smith ... 201 Hair Gel $5.99 Find the name and hire date of the manager working on the sales manual project Schemas Schema - A description of the database Subschema – describes a subset of the database and which users have access to this subset Data Definition Language Language Used to describe Schemas and Subschemas Describes relationships between different data Provides a Logical view of the data Data Dictionary Entry A more detailed description of the data in a database Specifies data types and ranges Assists programmers in understanding the data Logical vs. Physical Access Paths Database Management Systems concentrate on Physical access to the underlying tables Concurrency control Query’s Creating/deleting tables MIS systems are often software packages that (Logically) interface with a DBMS monthly reports charts automated inquiries