|Some EAR Models (Entity-Attribute-Relationships)
- Draft Logical Data Structures
The following Logical Data Structures (LDS) are models which have been used for student database assignments.
|Sports Clubs and Events||CD/Video/Tape Library|
|Route Mapping||Motorcycle Servicing and Sales|
|Tool Hire||Wine-to-Course Allocation|
|Sports Clubs and
The first LDS describes the situation:
A person may attend a number of training sessions.
A training session is attended by zero or more persons.
The next LDS describes a database which stores information about a number
People may be members of more than one club (and naturally a club usually has more than one member.)
The people have skills which are used in or related to their membership of a club (or clubs).
In the databases described by the following 2 LDS's, a player's performance in matches is recorded, from slightly different perspectives.
|This LDS describes the situation:
Club members attend events.
Members each have one particular ability (which is used in the event).
Each member has a rank
(It can justifiably be argued that 'Rank' and 'Position' should be entities in the same way, and for the same reason, that Ability is an entity.)
An attempt at a general model for a CD/video/tape library.
A star/artist appears in/on a number of films/cds/tapes.
If this describes a tape/cd library, could the 'Link' entity become 'Track'?
The next LDS describes a database to store information about routes
used for training and testing advanced motorcyclists.
A route is made up of a number of sections. Each section is a stretch of road, which has a 'difficulty' rating. A stretch of road has a start and end points which are named locations. A road section may be used in a number of routes.
|A database to track motorbike maintenance.
||And a database to track changes in second-hand
What wine would you like with this course, sir, madam?
A database to keep track of articles found
in different magazines and journals.