Re: RDBMS

> What is the main difference between DBMS & RDBMS.

"R". (somebody had to say it). :-)

Seriously, many of the DBMS systems of the 1970s stored data in a collection of records, linked together into either hierarchies or networks by pointers to records stored in other records, much the way a hypertext link is stored in another html page. These systems were legitimately labeled as DBMS products, but not as RDBMS products.

The Relational DBMS systems were distinguished from the hierarchical or network DBMSs by the fact that the relationships were expressed as data values, not as pointers. There are a host of other standards a "true relational"
system is supposed to adhere to, according to the originators of the concept. These standards are often more honored in the breach than in the observance.

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Regards,
    David Cressey
    www.dcressey.com