A relational model of data for large shared data banks

• data model 1

future users … protected from having to know how the data is organized …

in tree and network model

the user (and his programs) exploits a collection of user access paths to the data … the consequence, … is that terminal activities and programs become dependent on the continued existence of the user access paths …

data language

concept of a universal data language

relational data model permits a universal data sublanguage based on applied predicate calculus …

provides a means of describing data with its natural structure — that is, without superimposing any additional structure for machine representation purposes.

the universality of the data sublanguage lies in its descriptive ability (not computing ability).

one important effect that the view adopted toward relational data … is in the naming of data elements and sets. Some aspects of this have been dis- cussed in the previous section. With the usual network view, users will often be burdened with coining and using more relation names than are absolutely necessary, since names are associated with paths (or path types) rather than with relations.

values

one relation … defined on several domains … Each of these domains is, in effect, a pool of values …

primary key

… one domain (or combination of domains) of a given relation has values which uniquely identify each element (n-tuple) of that relation

external news

relational brought databases to the masses. Decades later, analyst IDC pegs the worth of the global relational database market at about $28bn — and it’s growing at 7.6 per cent a year. Some of the biggest and most profitable names on the computing scene — Oracle, IBM and Microsoft — are currently working on relational database management systems.¹