6. Databases GapFill

When storing data in tabular form, two broad classifications of database exist.  A  table-basedmono-filetabularflat-file system is a single table, which can be represented using a spreadsheet application.  A  relationalmulti-tableintegralone-to-many database comprises more than one table, with the tables connected together in some way.

Each table comprises  fieldsrecordsvaluesentities, each of which occupies a column within a table, and  valuesrecordscategoriesfields, each of which occupies a row.  Certain fields play specific roles within a table.  A  composite keysecondary keyprimary keyforeign key is used to uniquely identify a record and cannot be NULL.  A  secondary keyadjunct keyprimary keycomposite key is a combination of fields that uniquely identify a record.  A  primary keysecondary keycomposite keyforeign key is another field that is also unique for each record although can be NULL.

When a database comprises multiple tables, they are connected using  interactionslinksinterrelationshipsrelationships, the most common of which being is 'one to many'.  At the 'one' end is a   primary keytertiary keysecondary keycomposite key, and at the 'many' end is a(n)  composite keyprimary keyforeign keysecondary key.  If we were to ensure that, say, a student can't enrol in a class, we would enforce  second normal formreferential integritykey-base pairingthird normal form.

When working with a database comprising multiple tables,  standardisationassociationstabilisationnormalisation is an important process that minimises data  redundancyconsistencyvalidityintegrity and makes subsequent changes more straightforward.