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Re: (repost) cdt glossary 0.1.1

From: paul c <toledobythesea_at_oohay.ac>
Date: Mon, 05 Jun 2006 00:23:07 GMT
Message-ID: <LPKgg.239772$P01.190126@pd7tw3no>


paul c wrote:

> mAsterdam wrote:
> 

>> ---------------
>> Glossary 0.1.1: "You keep using that word.
>> I do not think it means what
>> February 2006 you think it means"
>> --------------- -- Inigo Montoya
>>
>>
>>
>> Maintainer: mAsterdam
>>
>> 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:
>> data (!), 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.
>>
>> What the glossary 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:
>> ---------------
>> The glossary is built from contributions.
>> 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, see the notes at the end.
>> ==============
>>
>>
>>
>> [Address]
>> A value, used to identify a location.
>> What is to be found there is up to the rest of the system.
>>
>> An address is a value used to locate ...
>> A reference is a value used to refer ...
>>
>> The difference between *locate* and *refer* is crucial here.
>>
>>
>>
>> [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.
>>
>>
>>
>> [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 definitions welcome, this goes for the rest as well,
>> of course.
>>
>> Some use 'class' as having exposed data.
>> Please be explicit about this if you do so.
>>
>>
>>
>> [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/Information#Information_is_not_data
>> (currently) says "information has meaning (i.e.: can inform),
>> while data does not. ".
>>
>> Somehow this "data has no meaning" idea has caught on.
>>
>> 1a. facts
>> 1b. a record on a medium of some fact in the real world.
>> 2. encoded information
>> 3. a combination of sign and meaning
>>
>> Warning: tongue in cheek definition
>> Information is what you want. Data is what you are given.
>>
>>
>>
>> [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)
>>
>>
>>
>> [Data model]
>> "an abstract, self-contained, logical definition
>> of the objects, operators, and so forth, that
>> together constitute the abstract machine with
>> which users interact. The objects allow us to
>> model the structure of data. The operators allow
>> us to model its behavior."
>> (C. J. Date, An Introduction to Database Systems,
>> 8e, 2003, p 15-16)
>>
>> 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.
>>
>>
>>
>> [Dimension]:
>> 1) A synonym for degree.
>> A relation R is of degree n if each tuple in R is an n-tuple.
>>
>> 2) An n-dimensional data structure, S, is one where each
>> element of S can be uniquely addressed as S[i1][i2]...[in]
>>
>> Note: Because a table in a SQL-DBMS can be seen as a
>> conventional visualization of a mathematical relation
>> where the dimension is as in 1) above, and can also be
>> manipulated using a general purpose programming language
>> with the dimension using 2) above being equal to 2, there
>> can be confusion when using this term.
>>
>> In this forum, use definition 1) freely and try to either
>> avoid 2) or be very clear, such as "2D array," when employing
>> definition 2).
>>
>>
>>
>> [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)
>>
>> "An entity is a 'thing' which can be distinctly identified. A specific
>> person, company, or event is an example of an entity. "
>> ("The Entity-Relationship Model-Toward a Unified View of Data", 1976, P.
>> Chen., http://www2.cis.gsu.edu/dmcdonald/cis8140/Chen.pdf )
>>
>> Edward Yourdon, who describes E/R in his work Modern Structured
>> Analysis, (Prentice Hall 1989) defines the concept of Entity
>> as having three properties:
>>
>> 1. Each representation of an entity can uniquely be identified
>> 2. Each representation of an entity is playing an important role in
>> the system it lives in. (it has to have a reason to be there)
>> 3. Each representation of an entity can be described by one or more
>> attributes (data-elements, like name, age, quantity)
>>
>> 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 distinguish it from the more
>> generic use of the term.
>>
>> For subtleties (e.g. strong and weak entity) -
>> please search the web.
>>
>>
>>
>> [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.
>>
>>
>>
>> [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, so take care to use it only when intending to inflame ;-)
>>
>>
>>
>> [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 dependent on A."
>>
>> 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
>>
>> Please be specific.
>>
>>
>>
>> [Information]
>> 0. data in context, data with meaning.
>> (This implies a definition of data as being without context,
>> without meaning - see data)
>> 1. new data to the receptor.
>> 2. available data, relevant to some decision or action.
>>
>>
>>
>> [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.
>>
>>
>>
>> [Key]
>> A value, used to identify something.
>> See also primary key, and (TO DO:) foreign key.
>>
>>
>>
>> [Meaning]
>> (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 usefulness 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.
>>
>>
>>
>> [MultiValue, MV]
>> 1. One name for the industry surrounding the Nelson-Pick data model.
>> In this context:
>> FILE: a real-world collective noun.
>> RECORD: a real-world object.
>> FIELD: is a real-world adjective.n.
>>
>> 2. A data field (or attribute) defined to permit a variable number of
>> values as a list (array).
>>
>>
>>
>> [NULL]
>> Roughly: a special marker that can be put in a place
>> inside a data structure where an actual value is expected.
>> Precisely what that marker means varies and there are at
>> least three possibilities that are sometimes assumed:
>>
>> (1) "Unknown value" This means that on the place of the marker
>> there should actually be a value but this value is not known
>> at the present time. For example, if a 'name' field in a tuple
>> describing a person is 'null' then this person will have a
>> name but we don't know it.
>>
>> (2) "Absent value" This means that the property that is
>> described by the value in question is simply not defined.
>> For example, if the 'shipping-date' field in a tuple
>> describing an order is 'null' then the order was
>> not shipped yet.
>>
>> (3) "Whatever SQL says it means" The exact meaning is hard to
>> summarize briefly, but is a mixture of the previous two
>> interpretations and involves a value with three truth-values
>> ('true', 'false' and 'unknown').
>>
>>
>> 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
>>
>> Note: Several better proposals have been made for this
>> entry. Unfortunately they all led to huge threads where
>> the maintainer couldn't decide which texts to quote here.
>>
>>
>>
>> [Object]
>> 1. Model of an entity, characterised by behaviour and state. (ISO)
>> 2. Something intelligible or perceptible by the mind.
>>
>>
>>
>> [Table/Row/Column] (SQL-DBMS)
>> Table: A collection of columns (the table header) and rows (the body).
>> 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.
>>
>>
>>
>> [Primary key] (SQL, not RM)
>> A key of a table, composed of one or more
>> named columns, uniquely identifies a row in a table.
>> A table can have only one primary key.
>>
>>
>>
>> [Type]
>> " TYPES are sets of things we can talk about;
>> RELATIONS are (true) statements bout those things."
>> -- Chris Date, feb 2004
>>
>> 1. Set of possible values (i.e. IT equivalent of math 'domain').
>> 2. Set of possible values plus
>> all possible operators defined on them. (i.e. synonymous to Class
>> if 'class' is meant to include a possible set of values).
>>
>> This is highly misunderstanding-prone area, so please
>> take some care to be specific.
>>
>>
>>
>> [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]
>> See address(*).
>>
>>
>>
>> [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.
>>
>>
>>
>> [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.
>>
>> 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.
>>
>>
>>
>> =============
>>
>> [[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.ATTRIBUTE ?
>>
>> In ER modeling, a RELATIONSHIP is defined over ENTITIES:
>> "A relationship is an association between several entities."
>> In RM, a RELATION is defined over VALUEs.
>> What is the difference between ENTITIES and VALUEs ?
>>
>>
>> =============
>>
>> [[TO DO]]:
>>
>> (please feel invited to write entries for these)
>>
>> Application
>> Attribute
>> Concept
>> Dynamic vs static
>> Hierarchy
>> Identity
>> Normalize
>> Location
>> Persistence
>> Operator
>> Orthogonal
>> Scalar
>>
>> Feel free to post suggestions to add or remove.
>>
>>
>>
>> How to contribute
>> -----------------
>>
>> Content:
>> Please keep in mind that the focus of the glossary
>> is on /real/ c.d.t. misunderstandings.
>>
>> Some discussions, after many sidetracks, are reducible
>> to /just/ different meanings and connotations of a word.
>> The differences could be resolved with just:
>> "Ah, now I see what you meant by that; next time I'll
>> be a little more careful in my choice of words".
>> Such words are nice glossary candidates.
>>
>> Examples from the past: Address, Domain.
>>
>> Sometimes, though, It's not just different connotation
>> or meaning which leads to the long winding talks
>> without communication. These differences go down to
>> deeply held strong opinions.
>> Some differences in the use of words run much deeper than
>> we can hope to clear up with just some definitions and
>> warning signposts. They might help a little anyway, so
>> these nastier entries are welcome, to.
>>
>> Examples from the past: NULL, Flat.
>>
>>
>> Form:
>> Please post your proposal as copy & pastable text,
>> with a subject line like this:
>>
>> subject: cdt glossary [Identity]
>>
>> Please also check spelling and grammar mistaeks.
>>
>> Thank you for contributing.
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> ----
>> Milestones? For the glossary I prefer inch-pebbles.
>>
> 
> 
> Okay, don't want to risk a premature definition but here's a stab at an 
> analogy/comparison for "persistence", a word that gets under my skin 
> most of the time I see it used here:
> 
> If nothing changes but the time of day, what was true yesterday is still 
> true today.
> 
> I may be wrong to see it this way, but this is why I don't associate the 
> acronym "rdms" with persistence, necessarily.
> 
> p
> 

  sorry, meant to say "if nothing else changes".

p Received on Sun Jun 04 2006 - 19:23:07 CDT

Original text of this message

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