c.d.theory glossary (repost)
Date: Thu, 13 May 2004 22:17:45 +0200
Message-ID: <40a3d7eb$0$21804$e4fe514c_at_news.xs4all.nl>
Eric Kaun wrote:
...
Preamble:
People tend to assume that words mean what they are
accustomed to, and take for granted that the other
posters have about the same connotations.
They don't always.
Some words are particularly suspect: database, object, normalisation.
Some just cause minor annoyances, the misunderstanding is cleared and
the discussion goes on: domain, type, transaction.
We don't know well-accepted, formal or comprehensive definitions
for everything. If you do have a useful reference, please provide it.
If an informal description is all we have, so be it.
> Ugh, can't find it - gone from my newsgroups.
This glossary seeks to limit lengthy misunderstandings in
comp.database.theory.
What the glossay is not:
The glossary is not a dictionary or encyclopedia, such as FOLDOC, Wikipedia (http://www.wikipedia.org), and the Web Dictionary of Cybernetics and Systems.
Specific links to serve the glossary's purpose are welcome, of course. Also, it does not try to be a FAQ for "all things database".
Credits & contributions:
Contributions from within this group are not credited, quotes from elsewhere are. This is no ironclad rule. It is just that the first contributors like it that way.
As a consequence, to all potential contributors: If you want your name stated please say so.
If you want to contribute, please do so in a copy&pastable way.
Note to native english speakers:
Please also check spelling and grammar mistaeks.
note:
Other definitons welcome, this goes for the rest as well,
of course.
[Database]
1. Deluxe filesystem
2. Shared databank (E. Codd)
[Domain]
Given a relation R, a domain is a set Sn such that for each tuple (A1,
A2, ...An, ...Am) in R, An is an element of Sn.
[Entity]
Thing of interest. (ISO)
[Function]
For now we have to live with *very different*
meanings of _function_ when talking about databases:
"The function of this function is to get the tuples from B
that are functionally dependant on A." Please be specific.
Three different contexts, but just about the same meaning:
General
A purpose or use.
Math
A binary mathematical relation with at most
one b for each a in (a,b).
Software
A subroutine, procedure, or method.
notes:
every operator is a function
every function is a relation
[MultiValue, MV]
1. One name for the industry surrounding the Nelson-Pick data model.
2. A data field (or attribute) defined to permit a variable number of values as a list (array).
[NULL]
The insanity bit. No! The humility marker.
mu: The absence of an answer to a question which requires an answer.
/adj./
1. Attributes to something the absence of values.
Ex: "The *null* set is the empty set, often represented by {}."
/n. colloq./
1. A noted appearance of the absence of values.
Ex: "This table contains *nulls*."
Common usage:
- Confusion arises when people use terms like "null value", a paradox to some, a contradictio in terminis to others.
- Confusion arises due to the fact that nullness (the absence of value) is often represented on computers by the number 0. (Obviously, 0 is not null.)
- In some contexts, 'null' and 'nil' mean the same thing; in others, they do not.
In databases traditionally NULL is used and and opposed. If you want to go into this, please first search for mu NIL void NULL undef, 2VL 3VL.
"It isn't the things we don't know that give us trouble. It's the things we know that ain't so." - Will Rogers
[Object]
1. Model of an entity, characterised by behaviour and state. (ISO)
2. Something intelligible or perceptible by the mind.
[Relation]
A relation is a subset of the set of ordered tuples (A1, A2, ... Am)
formed by the Cartesian cross-product of sets S1 x ... x Sm where each
An is an element of Sn.
Note: A set, Sx, is not restricted from participating as a member
of a relation more than once.
Distinction between identical sets in math is possible through ordinal
numbering such that given sets Sx and Sy, x <> y AND Sx is a subset of
Sy and Sy is a subset of Sx; in relational theory, in contrast, it is by
attribute name.
[Transaction]
A set of database operations constituting a logical unit of work.
Most DBMS include the ability to rollback complete transactions
when an error is detected.
[[ToDo]]:
Attribute
Normalize (There are some notes by Dawn)
Persistence
Type
Orthogonal
Feel free to post suggestions to add or remove.
[[Issues]]
RELATIONs vs. RELATIONSHIPs
Can namespaces help to make some distance? In this case:
RM.RELATION vs. ER.RELATIONSHIP
REPRESENTED vs. DESCRIBED
RELATION(SHIP)s vs RELATION(SHIP)s SET
fact vs. thing (ENTITY).
First Order Logic vs. Higher Order Logic.
What, if there is, is the equivalent of an ENTITY(SET) in the RM ?
Does it make sense to talk about ATTRIBUTES of a FACT ? How are those different from ATTRIBUTES of an ENTITY ?
Traditionally there can be Multivalued ATTRIBUTES
in ER, RM has atomic ATTRIBUTES.
So: RM.ATTRIBUTE and ER.ATRRIBUTE ?
In ER modeling, a RELATIONSHIP is defined over ENTITIES: "A relationship is an association between several entities." In RM, a RELATIONSHIP is defined over VALUEs. What is the difference between ENTITIES and VALUEs ?
How lossless is lossless decomposition?
What does it take for a pizza to be a pizza ?
Thank you for contributing.
Milestones? For the glossary I prefer inch-pebbles. Received on Thu May 13 2004 - 22:17:45 CEST