| 1.4 XML Equals SQL
Everywhere XML is being touted as the
most significant event in data exchange since SQL. XML provides a loosely coupled
interchange of data that is very similar to SQL. However, XML is much more general than
SQL, and it includes the ability to exchange data between application programs and
browsers, between application programs and other application programs or subroutines,
between application programs and post-processing utilities, and between application
programs and databases. Consider the difference between traditional fixed record I/O
formats and SQL databases. Whenever a file format changes, all programs using the file
must be reviewed and recompiled, in some cases after maintenance modifications are made
but also for programs which require no maintenance changes at all. Thus, fixed record I/O
forces a tightly coupled data exchange. By contrast, SQL databases allow a unique
definition of each data item for each program. Data items receiving SQL data need not have
the same definition as the database column. When a database table changes, only programs
whose logic is directly impacted by the change need to be reviewed, modified and
recompiled. As a result, SQL provides a loosely coupled data exchange.
Other than SQL databases, all current data exchange is
tightly coupled. Data file formats are fixed and must agree exactly for all users of that
file. Data exchange between a fixed screen format and interpretive middleware is similarly
tightly coupled. Data exchange between application programs, either through a CALL
interface or through message passing, is almost always through a fixed format that must
agree exactly. Users of EDI as well as tightly coupled architectures such as DCOM and
CORBA are all familiar with the limitations and burdens imposed by the fixed structure.
Adopting a loosely coupled data exchange architecture based
on XML not only removes the need for middleware with its attendant maintenance burden, but
it reduces the maintenance burden across all programs, which must share data. XML
addresses this maintenance burden in three ways: decreased cost of maintenance, increased
reliability of software, and decreased time to implement changes (i.e., time to market).
With the responsiveness required for the new competitive environ-ment being expressed in
Internet time, perhaps the greatest benefit of XML will be the decrease in the time
required for reliably changing software. |
