Database Reference
In-Depth Information
Essentially,youcouldstoredatainanetwork/hierarchy…buthowwouldyouever
getitbackout?
Attribute
Tuple
Relation
Relational database terminology
Codd wrote several papers on a different approach to database management
systems that would not rely as much on linked lists of data (networks or hierarchies)
but more on sets of data. He proved—using a mathematical representation called
tuple calculus—that sets would be able to adhere to the same requirements
that navigational database management systems were implementing. The only
requirement was that there would be a proper query language that would ensure
some of the consistency requirements on the database. This, then, became the
inspiration for declarative query languages such as Structured Query Language,
SQL. IBM's
System R
wasoneoftheirstimplementationsofsuchasystem,but
Software Development Laboratories, a small company founded by ex-IBM people
and one illustrious Mr. Larry Ellison, actually beat IBM to the market. Their product,
Oracle, never got released until a couple of years later by Relational Software, Inc.,
andtheneventuallybecamethelagshipsoftwareproductofOracleCorporation,
which we all know to day.
With relational databases came a process that all of us that have studied computer
science know as
normalization
. This is the process that database modelers go
through to minimize database redundancy and introduce disk storage savings, but
introducing dependency. It involves splitting off data elements that appear more
than once in a relational database table into their own table structures. Instead of
storing the city where a person lives as a property of the person record, I would split
the city into a separate table structure and store person entities in one table and city
entities in another table. By doing so, we will often be creating the need to join these
tables back together at query time. Depending on the cardinality of the relationship
between these different tables (1:many, many:1, and many:many), this would require
the introduction of a new type of table to execute these join operations: the join table,
which links together two tables that would normally have a many:many cardinality.
