Databases
StackOverflow2013
Postsdbo
POdatabase supertype/subtype
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POdatabase supertype/subtype
    primarykey
    data
    text
    <p>I need to implement a database to track a parcel's location.</p> <p>There can be basically 4 locations, namely on a aeroplane, on a ship, on a car, at a transit office.</p> <p>I need to have separate entities for these 4 locations because they all have mutiple instances of each (e.g. many aeroplanes, many cars)</p> <p>Also, each of these 4 entities are managed by one and only one employee (another entity).</p> <p>I have created an associative entity called job whereby it stores the information about which employee working in each of the 4 locations, similar to a flight number which contains the aeroplane id with the pilot id.</p> <p>I have examined the attributes of the 4 locations, and found that they could be classified into car being the supertype and aeroplane, ship and office being subtype of car.</p> <p>there would be a unique attribute of location_id which tells me whether it is on an aeroplane or an office in the supertype, thus the subtype would inherit this attribute.</p> <p>my question is whether in the tables design, since locations will be separated into four different tables, whenever i referred location_id(FK) from the job entity, is it still possible to do so since a foreign key normally links to only one table and not 4 tables in this case..</p> <p>EMPLOYEE [ <strong>employee_id</strong>, employee_name, gender, contact_number, job_scope ]</p> <p>JOB [ <strong>job_id</strong>, (employee_id), (location_id) ]</p> <p>OFFICE [ <strong>location_id</strong>, office_id, address ]</p> <p>CAR [ <strong>location_id</strong>, vehicle_id ]</p> <p>AEROPLANE [ <strong>location_id</strong>, vehicle_id, type, unladen_weight ]</p> <p>SHIP [ <strong>location_id</strong>, vehicle_id, size ]</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. This table or related slice is empty.
    1. USuser776914
    plurals
    1. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POdatabase supertype/subtype
      1. This table or related slice is empty.
      1. VTUpMod
    1. COWe seem to have a little misunderstanding here, my bad. See my updated answer below.
      singulars
      1. POdatabase supertype/subtype
      1. USp.marino
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload