Re: cdt glossary 0.1.0

mAsterdam <mAsterdam@xxxxxxxxxxx> wrote:

MAINTAINER: mAsterdam

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.

What you might have to do is characterize some context, and then list
the jargon. Another context, other jargon. And then establish some
degree of correspondence, perhaps characterized as strong, weak and
exact. You have things like General, Math, Software.

If you used that dreaded word, entity, in an ER context, and matched
it to, relation, in the context of the RM, you might omit, entity, in
such a correspondence chart for the RM. Yet the RM might refer to
entities, otherwise. You might use, instance, in an object structure
and yet also wish to use it synonymously in the context of the RM. And
so on.


[Change management]
Many organizations have a CM process in place in
order to make their evolution more manageable.
The organization of data within a database can
and will change with these changing circumstances.
A DBMS should provide facilities to support this.
Changing the underlying structure should be
possible without affecting what is already stored.
For example, you can add a column to a table without
losing what is already there.

Related adjectives: maintainable, agile, flexible, adaptive.

And which might be aided by enforcing manipulation of the database by
one avenue, and one only, such as through the use of SQL.


[Data]
"Known facts that can be recorded and have implicit meaning."
-- Fundamentals of Database Systems, Elmasri & Navathe.

When people discuss data in the context of database,
they are usually talking of something with meaning.
There are people who think that data doesn't need
to mean anything. http://en.wikipedia.org/wiki/Data
(currently) says "data may have no meaning".
Somehow this "data has no meaning" idea has caught on.

1a. facts

Including scale, domain, dimension. A quart is not the same as a
British pound.

1b. a record on a medium of some fact in the real world.

Which begs the question, when is data, fact, and fact, data. Or should
they simply be used interchangeably?

2. encoded information

Or instead of limiting to scalars, just call it a character string.

3. a combination of sign and meaning



[Database]
"A logically coherent collection of related real-world data
assembled for a specific purpose." -- rephrased from
"Fundamentals of Database Systems", Elmasri & Navathe.

1. Deluxe filesystem
2. Shared databank (E. Codd)

By logically coherent, they mean - ordered. By order comes both
insertion and retrieval. And organized collection, if one prefers.

It need not be anything from the "real-world". A database of some
fantasy skid, or the meanderings of Alice in the woods, would still be
an organized collection, just of otherwise meaningless phrases.


[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.

From one dimension, such as distance, mass, etc. One scale, for
scalars, in a particular attribute.


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.

A date is still dimensional data. Scalars or character strings, in
other words.


[Entity]
Thing of interest. (ISO)

This term is often used when doing conceptual data modeling.
When it is used with a particular product, technique, or technology,
such as XML, refer to the use of the term within that "namespace" using
an adjective, such as "XML entity" to distinquish it from the more
generic use of the term.

For subtleties (e.g. strong and weak entity) -
please search the web.

I still think it's a rather vague term, with many applications in
various context.


[Fact]
1. A piece of information about circumstances that exist or
events that have occurred

Semantically so, but not necessary for data. Perhaps this is where the
confusion comes in asserting that data is unfettered from structure or
meaning. The data may be of something that could exist in a
probabalistic state, or similarly in some future state, in the future,
or was said to have been by some, and not by others of another view or
faction, etc. In the eye of the beholder, to a degree. But the string
or scalar remain.

2. A concept whose truth can be proved.

But by who, faction A, or faction B? Faction A excises and censors it
from their webpage. Faction B makes a minor mistake and faction A
says, see - there.

3. A statement or assertion of verified information.
4. An event known to have happened or something known to have existed.

You would think everyone could agree. But this is precisely where they
don't. I think the data is a datum. It's stored, retrieved and
manipulated. It need mean nothing at all, or at least not to one
faction. But it is organized, structured and manipulated in that way
according to rules and contraints. And that structure is its truth.
The order is what makes it information, or 'fact', or what have you,
at least to someone. Change that order, and something else is
represented, quite simply.


[Flat]
1) An object which by any definition could be considered as 2
dimensional might informally be called flat.

2) (controversial:)
The absence of hierarchy (multiple levels of details).

Note: Any use of the term flat tends to be seen as inflammatory by
someone

Saying anything at any time is going to enrage some, no doubt. That
can never be the test for inclusion in some glossary, unless again,
factions rule. And factional definitions give way to those more
balanced, even if sometimes by poor reading light or the back room of
the bar, etc, wherever the 'resistance' can gather.


[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."

Three different contexts, but just about the same meaning:

General
A purpose or use.

function - tasks, implying occupation, office, etc.
function - (un)intended use, hammer for nails, for demolition,
heart pumping blood, etc.
functional - able to perform, within some limit
function - loose synonym for a formal gathering

Math
A binary mathematical relation with at most
one b for each a in (a,b).

function - equation for a given independent variable on some
domain yielding a single dependent variable result on some range for a
given predicate, with the independent variable having a one to one or
many to one relationship with the result
function - the relation mapping the independent domain to the
dependent domain, as one to one or many to one.


Software
A subroutine, procedure, or method.
function - a callable procedure which returns some result
function - method of a class procedure, implicit call

notes:
every operator is a function
every function is a relation

Yes.


[Information principle] (RM)
Date/Codd:
Chris Date in "EDGAR F. CODD 08/23/1923 ? 04/18/2003 A TRIBUTE":
The entire information content of a relational database
is represented in one and only one way: namely, as
attribute values within tuples within relations.

But typically found stated as:

Codd's #1 of 12 Rules: All information in a relational database is
represented explicitly at the logical level and in exactly one way -
by values in tables.


[Key]
A value, used to identify something.
See also TODO: primary key, foreign key.

Codd's #2 of 12 Rules: Each and every datum (atomic value) in a
relational database is guaranteed to be logically accessible by
resorting to a combination of table name, primary key value, and
column name.

The primary key (PK), composed of one or more named columns, uniquely
identifies the record in that named table.


[Object]
1. Model of an entity, characterised by behaviour and state. (ISO)
2. Something intelligible or perceptible by the mind.

In the programmer's interface to an object model: a class with
properties and/or methods, whether principally a table/data or a
procedure.

Object - you know it when you see it.


[Table/Row/Column] (SQL-DBMS)
Table: A collection of columns (the table header) and rows (the body).

Table - a tabular grid, not necessarily surrounded by chairs

Row: A collection of values, conforming to the table header columns.

One table may contain data about one entity,
about several entities, about one or several
relationships or any combination.
A column can be seen as the attribute of the
entity/one of the entities/relationships
about which the table is concerned.

Depends on the sense for the term, entity.


[Pointer]
See address(*).

Pointer - redirection vector
Pointer - link
Pointer - data type/format
Pointer - dog's name (but not applicable in this context)
And:

[References, pointers, keys]

While references may be implemented as pointers,
the programmer prefers not to know (if he prefers
to know he should have used pointers).

In some programming languages one can declare
variables of a pointer type - these variables
can have pointer values.
m.m. (mutatis mutandis) reference.

Two operations are supported:
referencing and dereferencing.
On references only these operations are possible.
On pointers other operations are possible.

The dereferencing operation takes a pointer
*value* and returns a pointer *variable* of
the type the pointer refers to.
The referencing operation is the inverse operation.
It takes a *variable* and returns a pointer *value*.
m.m. reference.

In Java the term pointer was avoided
because pointer is often used to mean
physical memory addresses.

Relational keys are not pointers.


[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.

Well, if a table is said to correspond to a "relation", then obviously
a relation is just an collection, or better set, of n-tuples, more
than simply ordered pairs, or 2-tuples.


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.


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 ?

Multi-valued as in more than one scalar or string/attribute?


(please feel invited to write entries for these)

Application
As a noun, loosely a stand-alone program as perceived by the
customer, rather than a component - spread***, but not necessarily
integrated into another application, etc.
Attribute
An aspect, a component
Concept
See entity
Dynamic vs static
Static meaning unchanging, dynamic subject to change
Hierarchy
Organization by category and sub-category
Scalar
A real or integer, with or without dimension



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