Database Reference
In-Depth Information
As you can probably imagine from the preceding discussion, these models were
very interesting and resulted in a number of efforts that shaped the database
industry. One of these efforts was the Conference on Data Systems Languages,
better known under its acronym, CODASYL. This played an ever so important role
in the information technology industry of the sixties and seventies. It shaped one of
the world's dominant computer programming systems (COBOL), but also provided
the basis for a whole slew of navigational databases such as IDMS, Cullinet, and IMS.
Thelatter,theIBM-backedIMSdatabase,isoftenclassiiedasahierarchicaldatabase,
which offers a subset of the network model of CODASYL.
Navigational databases eventually gave way to a new generation of databases,
the Relational Database Management Systems. Many reasons have been attributed
to this shift, some technical and some commercial, but the main two reasons that
seem to enjoy agreement across the industry are:
• The complexity of the models that they used. CODASYL is widely
regarded as something that can only be worked or understood by
absolute experts—as we partly experienced in 1999, when the Y2K
problem required many CODASYL experts to work overtime to
migrate their systems into the new millennium.
• The lack of a declarative query mechanism for navigational database
management systems. Most of those systems inherently provide a very
imperativeapproachtoindingdata:theuserwouldhavetotellthe
database what to do instead of just being able to ask a question and
having the database provide the answer.
This allows for a great transition from navigational to relational databases.
Relational databases
Relational Database Management Systems are probably the ones that we are most
familiar with in 21st century computer science. Some of the history behind the
creation of these databases is quite interesting. It started with an unknown researcher
at IBM's San Jose, CA, research facility; a gentleman called Edgar Codd. Mr. Codd
was working at IBM on hard disk research projects, but was increasingly sucked
into the navigational database management systems world that would be using
these hard disks. Mr. Codd became increasingly frustrated with these systems,
mostly with their lack of an intuitive query interface.
