General-purpose and special purpose DBMSs

A DBMS has evolved into a complex software
system and its development typically requires
thousands of person-years of development
effort. [4] Some general-purpose DBMSs such
as Adabas, Oracle and DB2 have been
undergoing upgrades since the 1970s. General-
purpose DBMSs aim to meet the needs of as
many applications as possible, which adds to
the complexity. However, the fact that their
development cost can be spread over a large
number of users means that they are often the
most cost-effective approach. However, a
general-purpose DBMS is not always the
optimal solution: in some cases a general-
purpose DBMS may introduce unnecessary
overhead. Therefore, there are many examples
of systems that use special-purpose databases.
A common example is an email system: email
systems are designed to optimize the handling
of email messages, and do not need significant
portions of a general-purpose DBMS
functionality.
Many databases have application software that
accesses the database on behalf of end-users,
without exposing the DBMS interface directly.
Application programmers may use a wire
protocol directly, or more likely through an
application programming interface . Database
designers and database administrators interact
with the DBMS through dedicated interfaces to
build and maintain the applications' databases,
and thus need some more knowledge and
understanding about how DBMSs operate and
the DBMSs' external interfaces and tuning
parameters.