chapter 5 relationships & queries in databases. types of relationships one to one examples?...
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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
NetworkDifficult to manage
and implement relationships
RelationalThe most popular
structure
Relational
CustomersCID FName LName Address
508 Eric Breimer ...
509 Andrew Zych ...
510 Greg Smith ...
ProductsPID Description Cost
199 Viagra $45.99
200 Tooth Paste $2.58
201 Hair Gel $5.99
OrdersOID CID PID Quantity
001 508 199 500,000
002 508 201 2
003 510 201 1
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