c.d. glossary 0.0.3
Date: Sat, 15 May 2004 19:01:07 +0200
Message-ID: <40a64cd7$0$575$e4fe514c_at_news.xs4all.nl>
- Computerese Irregular Verb Conjugation: Glossary 0.0.3: I have preferences. may 15, 2004 You have biases. He/She has prejudices.
- -- Gene Wirchenko
Preamble:
This glossary seeks to limit lengthy misunderstandings in comp.database.theory. This newsgroup uses terms from database modeling, design, implementation, operations, change management, cost sharing, productivity research, and /or basic database research.
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.
It consists of signposts: watch out! You may think the OP means A but she might mean B. Alternative names and views of the same concept are introduced when the danger of mutual misunderstandings is appearant. When context matters, it is provided. The glossary is a highly biased list of problematic concepts.
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.
Some are simply voted in even if there has been no real
misunderstanding: data. My preference/bias/prejudice:
I sincerely hope the focus stays on the suspect category.
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.
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:
The glossary is built from contributions.
Generally contributions from within this group are not credited, quotes from elsewhere are. 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.
[Class]
A class is what provides a name and a place for
the abstract behavior of a set of objects
said to belong to the class. (Larry Wall, Apocalypse 12)
note:
Other definitons welcome, this goes for the rest as well,
of course.
[Data]
1. facts
2. encoded information
[Database]
1. Deluxe filesystem
2. Shared databank (E. Codd)
[Domain]
1. 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.
2. A domain is a set of values: for example
"integers between 0 and 255", "character strings less than 10 characters long", "dates".
Sometimes used synonymously with type.
[Entity]
Thing of interest. (ISO)
[Function]
For now we have to live with 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]
1. 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.
2. ...
[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]]:
Application
Attribute
Dynamic vs static
Normalize (There are some notes by Dawn)
Partitioning
Persistence
Operator
Orthogonal
Scalar
Type
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 ?
A quote:
" TYPES are sets of things we can talk about;
RELATIONS are (true) statements bout those things." -- Chris Date, feb 2004
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 Sat May 15 2004 - 19:01:07 CEST