What is a "data sublanguage"

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David Cressey - 18 Dec 2007 16:19 GMT

It's time for me to ask another dumb question.

The term "data sublanguage" appears in Codd's 1970 paper. I kind of glossed
over it when I first read it, figuring that my intuitive grasp was close
enough. Now I'm wondering whether I really know what "data sublanguage"
means, at all.

What is a "data sublanguage"? What is the difference between a
"sublanguage" and a "language"? Can a programming language embed a data
sublanguage as a subset of the syntax and semantics of the programming
language? Does the data sublanguage Codd was referring to span all the
syntax and semantics of the relational data model?

Did SQL take the place of the data sublanguage Codd was suggesting should be
built? Have Date & Darwen or others created a relational data sublanguage?

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Kira Yamato - 18 Dec 2007 17:03 GMT

> It's time for me to ask another dumb question.
>
[quoted text clipped - 11 lines]
> Did SQL take the place of the data sublanguage Codd was suggesting should be
> built? Have Date & Darwen or others created a relational data sublanguage?

Do you have Date's book An Introduction to Database Systems? It seems
to have all the answers to all of your questions.

Signature

-kira

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Roy Hann - 18 Dec 2007 18:20 GMT

> Do you have Date's book An Introduction to Database Systems? It seems to
> have all the answers to all of your questions.

The term sublanguage has always sat awkwardly with me too, so I have just
glanced at the above-named book again, but I can't find the term
"sublanguage" in the index. It doesn't appear in Date's Relational Database
Dictionary either. Perhaps you could give a page reference?

If SQL is a sublanguage, then it might be to language what a subhuman is to
a human. ;-)

Roy

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Kira Yamato - 18 Dec 2007 19:47 GMT

>> Do you have Date's book An Introduction to Database Systems? It seems to
>> have all the answers to all of your questions.
[quoted text clipped - 8 lines]
>
> Roy

I have the 7th edition. It is on page 37, section 2.3 The External Level.

Signature

-kira

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Bob Badour - 18 Dec 2007 21:35 GMT

A sublanguage is simply a proper subset of a language devoted to some
identified task. SQL has DML and DDL sublanguages. Some languages
support embedding SQL as a sublanguage through a pre-processor etc.

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Knowledgy - 25 Dec 2007 17:10 GMT

In relational database theory, the term sublanguage, coined by E. F. Codd in
1970, refers to a computer language used to define or manipulate the
structure and contents of a relational database management system (RDBMS).
Typical sublanguages associated with modern RDBMS's are QBE (Query by
Example) and SQL (Structured Query Language). In 1985, Codd encapsulated his
thinking in twelve rules which every database must satisfy in order to be
truly relational. The fifth rule is known as the Comprehensive data
sublanguage rule, and states:

A relational system may support several languages and various modes of
terminal use (for example, the fill-in-the-blanks mode). However, there must
be at least one language whose statements are expressible, per some
well-defined syntax, as character strings, and that is comprehensive in
supporting all of the following items:
Data definition
View definition
Data manipulation (interactive and by program)
Integrity constraints
Authorization
Transaction boundaries (begin, commit, and rollback)

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Sincerely,
John K
Knowledgy Consulting, LLC
www.knowledgy.org
Atlanta's Business Intelligence and Knowledge Management Experts

> It's time for me to ask another dumb question.
>
[quoted text clipped - 14 lines]
> built? Have Date & Darwen or others created a relational data
> sublanguage?

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