[es] - Par pitanja u vezi terminologije...

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Par pitanja u vezi terminologije...

^{15.05.2007. u 09:07 - pre 206 meseci}

Čitam neku literaturu o strukturama i bazama podataka (nešto interno sa jednog fakulteta), pa bih hteo
a priupitam u za par 'sitnica' vezanih za terminologiju.

Radi se o pojmovima (entity), (entity class) i (entity occurence, entity instance).

Entity je prevedeno kao entitet.
Entity class je prevedeno kao tip entiteta.
Entity occurence, entity instance je prevedeno kao pojava entiteta.

Pitanja:

Da li je Entity konkretan objekat, na primer (petar, petrovic, 11-11-1911), ili drugim rečima jedan konkretan slog podataka ?

Da li je Entity tabela (ne podaci, nego struktura koja je definisana skupom atributa)?

Da li je Entity Class tabela?

Da li su Entity i Entity Class sinonimi, tj. iz konteksta se razrešava da li se radi o konkretnom slogu ili tabeli?

Šta je onda u svemu tome Entity occurence, entity instance?

_{[Ovu poruku je menjao X Files dana 15.05.2007. u 10:29 GMT+1]}

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Re: Par pitanja u vezi terminologije...

^{15.05.2007. u 16:11 - pre 206 meseci}

Citat:

About Entities

Entities contain attributes, which are characteristics or modifiers, qualities, amounts, or features. An attribute is a fact or nondecomposable piece of information about an entity. Later, when you represent an entity as a table, its attributes are added to the model as new columns.

You must identify the entities before you can identify the database attributes. After you determine the entities, ask yourself, "What characteristics do I need to know about each entity?" For example, in an address entity, you probably need information about street, city, and zip code. Each of these characteristics of the address entity becomes an attribute.

Citat:

About Entity class

When Dr. Chen developed entity/relationship modeling [1] (commonly known as data modeling), he used the term entity type to define the boxes on his diagrams as representing classes of things. For example "Person" would be an entity type, and "Sally Jones" would be an entity or an instance of the entity type. Over the years, however, practitioners became sloppy, and the term entity came to refer to the class of things.

Then the object-oriented community came to the fore with it's use of the terms class and object, where object was clearly an instance of a class. In their criticism of the entity/relationship community, they claimed that the object-oriented approach more correctly represented the concept of class.

This of course was mistaken, because data modelers have always been clear on the distinction between the definition of a class of things and instances of those things. The problem was sloppy usage.

In the interest of clarity of language, therefore, the term entity class will henceforth be defined as the definition of a kind of thing of significance to an organization. Conceptual data models will thus be composed of entity classes, attributes, and the relationships between pairs of entity classes.

Citat:

About Entity Occurrences

An additional data object is the entity occurrence. Each row in a table represents a specific, single occurrence of the entity. For example, if customer is an entity, a customer table represents the idea of customer; in it, each row represents one specific customer, such as Sue Smith. Keep in mind that entities become tables, attributes become columns, and entity occurrences become rows.

Nadam se da sam bar malo otvorio puteve ka nekom razjašnjenju.

Someone's sitting in the shade today because someone planted a tree a long time ago.

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Re: Par pitanja u vezi terminologije...

^{15.05.2007. u 16:42 - pre 206 meseci}

Oce ljudi da dokazu da je relational theory u stvari podskup objektnog modela, pa ih nije mrzelo da pisu i knjigu

Ako definisemo simbol '<------>' recima 'odgovara otprilike', koliko se secam, moze da se kaze ovako:
Entity <-----> tabela, entitet
entity instance <-----> red u tabeli (ne 'slog', slog je u file sistemima, u relacionim tabelama je 'red' ili 'row', i nije 'polje' nego 'kolona')

I tu se svaka slicnost zavrsava, ma kako se trudili da cetvrtastu sipku uguramo u okruglu rupu.

U knjizi "An Intrduction to Database Systems', by Chris Date, imas na kraju raspravu i uporedjenje OO i relacionog modela, sta moze jedan a sta moze drugi, sta ne valja ovde i sta ne valja tamo, i koliko ima preklapanja. OO pored svoje pretpostavljene univerzalnosti i superiornosti nije uspeo da iznedri sistem za cuvanje podataka u realnom vremenu i prostoru, pa se jednostavno pozajmljuje od postojecih relacionih i kvazi relacionih (would be) sitema. Uz malo truda i srece na kraju moze se dobije koliko toliko pristojan proizvod (web/windows aplikacija plus baza).

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X Files
Vladimir Stefanovic
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Re: Par pitanja u vezi terminologije...

^{15.05.2007. u 20:07 - pre 206 meseci}

Hvala svima.

Sad mi je lakse. Taman sam pomislio da sam iznenada postao nesposoban da pratim literaturu :)

Neko napise knjigu, onda neko drugi to prevede, onda neko treci to (pro)tumaci i napravi skriptu.

Citat:

ne 'slog', slog je u file sistemima, u relacionim tabelama je 'red' ili 'row', i nije 'polje' nego 'kolona'

Da... moja geška. Slog je fizički pojam (ako se ne varam), a red/kolona je logički.

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