RDBMS

RDBMS

A relational database management system (RDBMS) is a database management system (DBMS)that is based on the relational model as introduced by E. F. Codd. Relational databases are the most common kind of database in use today (assuming one does not count a file system as a database). A short definition of an RDBMS may be a DBMS in which data is stored in the form of tables and the relationship among the data is also stored in the form of tables.

History of the term

E. F. Codd introduced the term in his seminal paper "A Relational Model of Data for Large Shared Data Banks", published in 1970. In this paper and later papers he defined what he meant by relational. One well-known definition of what constitutes a relational database system is Codd's 12 rules. However, many of the early implementations of the relational model did not conform to all of Codd's rules, so the term gradually came to describe a broader class of database systems. At a minimum, these systems:presented the data to the user as relations (a presentation in tabular form, i.e. as a collection of tables with each table consisting of a set of rows and columns, can satisfy this property) provided relational operators to manipulate the data in tabular form.The first systems that were relatively faithful implementations of the relational model were from the University of Michigan; Micro DBMS (1969) and from IBM UK Scientific Centre at Peterlee; IS1 (1970–72) and its followon PRTV (1973–79). The first system sold as an RDBMS was Multics Relational Data Store, first sold in 1978. Others have been Berkeley Ingres QUEL and IBM BS12.The most popular definition of an RDBMS is a product that presents a view of data as a collection of rows and columns, even if it is not based strictly upon relational theory. By this definition, RDBMS products typically implement some but not all of Codd's 12 rules.A second, theory-based school of thought argues that if a database does not implement all of Codd's rules (or the current understanding on the relational model, as expressed by Christopher J Date, Hugh Darwen and others), it is not relational. This view, shared by many theorists and other strict adherents to Codd's principles, would disqualify most DBMSs as not relational. For clarification, they often refer to some RDBMSs as Truly-Relational Database Management Systems (TRDBMS), naming others Pseudo-Relational Database Management Systems (PRDBMS).Almost all commercial relational DBMSes employ SQL as their query language. Alternative query languages have been proposed and implemented, but very few have become commercial products.

Market structure

Low adoption costs associated with open-source RDBMS products such as MySQL and PostgreSQL have begun influencing vendor pricing and licensing strategies. Your institution likely has a library containing a wide variety of books and journals. Part of the educational process is learning how to do research. It would be wrong of me to take that learning process away from you. You should have classmates, teaching assistants, and course instructors to which questions may be directed. If you have not yet exhausted those three sources of course assistance, you should not contact me. But even if you have exhausted those sources, there are no guarantees that I will attempt to be of assistance. I will emphatically not be providing customized assignment solutions.When you are considering which database you might wish to use, it would be worth looking at the essay Finding Technology Solutions. It represents a discussion of how to search for technology solutions, and starts with a simple premise: “Don’t assume a solution until you have determined what problem you need to solve."It is also interesting to note that SQL is not synonymous with “relational databases." Just like ODBMS are often database construction kits or persistence libraries, SQL DBASE’s are a real DBMS (they do provide transactions, recovery, concurrency control, some data integrity) + a relational construction kit. Meaning that by a skillful use of SQL one can come somewhere close to a relational database.But the complexity is left on the user to shoulder, and it is very difficult to stretch SQL so that you are still in the realm of relational model. And guess what: most users don't and most users suffer as a consequence. Some databases are little more than a light layer of syntactic frosting on top of a flat file storage system. For instance, an xBase system is a set of flat files, with a thin veneer of "database language" put on top, almost surely not deserving of the "relational" moniker, even when they get some SQL-like query language. Some databases with SQL in their names are hardly relational in nature.