cdt

Here are some proposed changes to the glossary from recent discussions.

Please take only one or two items at a time for easy harvesting :-)

I apologize for the clumsy subject line. When I repost the whole thing I'll use
"c.d.theory glossary 0.0.4"

ADDITIONS (comments welcome)

[address]

A value, used to identify a location.

[change management]

The organization of data within a database can and will change with circumstances. A DBMS should provide facilities for changing the underlying structure without affecting what is already stored. For example, you can add a column to a table without losing what is already there.

[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 on its own has no meaning". Somehow this "data has no meaning" idea has caught on.

1.a. facts
1.b. a record on a medium of some fact in the 'real world'.
2. encoded information
3. 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.

[data model]

Data models are artificial constructs and may not completely represent the true nature of information and categorization. These categories already exist, to some degree, in the way information is handled outside the database.
Databases don't exist in vacuo; they're fed (and consulted) by users who would have some system of mental categorization even if they were shuffling everything around with paper and pencil.

Source ?? (link was dead when I checked)

[fact]

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

2. A concept whose truth can be proved.
3. A statement or assertion of verified information.
4. An event known to have happened or something known to have existed.

[information]

0. data in context, data with meaning.
(Implies a definition of data as being without context, whithout meaning - see data)
1. new data to the receptor.
2. available data, relevant to some decision or action.

[information principle]

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.

[key]

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

[MV]

Anthony W. Youngman (PICK File, record, field)

   FILE: a real-world collective noun.
   RECORD: a real-world object.
   FIELD: is a real-world adjective.n.

[type - 3rdM]

In The Third Manifesto a type is:

• a pattern (possible representation)
• a domain for some operators (THE_xxx operators)
• a codomain for some operators (the "constructors")

There is a requirement for the 'domain' and the 'codomain' to be the same set.

[pointer]

A pointer is an address(*) used to locate something. What is to be found there is up to the rest of the system.

[reference]

A reference is a value, used to refer to something. A program can get the current value of that something (without ever knowing where it resides) by dereferencing, even if that something has been relocated between the time of first reference and the dereferencing.

[ISSUES] ==== comment necessary :-)

[meaning vs use]

Say we currently have a validated statement about the exchange rate of some stock at some recent time.

1. It does not matter to the meaning where/how this statement is represented. We have it.
2. To the use of it it is important where/how it is represented, and available to relevant actors.
3. Twenty years later the meaning of this statement is still the same.
4. Twenty years later most of its usefullness will probably have gone.

It may be --- in some instances -- not appropriate to make this distinction. The meaning of data is always contextual. The same bit of data means different things to different structured viewpoints within the organization, for example, and at different times (epochs). One grain of sand does not form a beach. One bit of data itself has little meaning. It is rather the collective of all data that possesses greater notion of meaning.

[pointers, references and keys]

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

A pointer is a special kind of type. One can declare variables of a pointer type, and these variables can have pointer values.

A pointer type is a type for which two operations are supported: referencing and dereferencing.

The dereferencing operation takes a pointer *value* and returns a *variable* of the type the pointer refers to.

The referencing operation is the inverse operation. It takes a *variable* and returns a pointer *value*.

Java references are pointers in the above sense. The term pointer was avoided in Java because the term pointer is often used in a more restricted sense, meaning physical memory addresses.

Relational keys are definitely not pointers.

[logical pointer]

logical pointers as in navigational information from a foreign key in one relation to a primary key in another (effectively a mapping).

[table, row, column]

table:
1. A sentence that has not yet been uttered, because it relates unknown values
2. A collection of rows and columns.

row:
1. A statement of fact, as an utterance of the "meta" sentence described above.
2. A collection of attributes.

column:
1. any piece of utterable information.
2. An attribute of an entity.

entity: ???

[primary key, foreign key]

uniquely (as in PK, CK) identify or relate (as in FK) Received on Sun Jun 06 2004 - 16:39:48 CEST