Re: Latest version of glossary

From: Alexandr Savinov <spam_at_conceptoriented.com>
Date: Fri, 24 Feb 2006 12:01:06 +0100
Message-ID: <43fee772$1@news.fhg.de>

x schrieb:
> "Alexandr Savinov" <spam_at_conceptoriented.com> wrote in message
> news:43feddcd$1_at_news.fhg.de...

>> x schrieb:
>>> "Alexandr Savinov" <spam_at_conceptoriented.com> wrote in message
>>> news:43fec3be$1_at_news.fhg.de...

>

>>>> In other words, without an identifier a thing is NOT an entity. Without
>>>> properties it is also NOT an entity.

>

>>> Without an identifier a thing is not a thing :-)

>

>> It depends how we define a thing. We can assume that a thing may exist
>> without an identifier or at least without an explicit identifier.

>
>

>> I also  can hardly imagine that but we need a kind of catch all term

> without any

>> constraints.

>
> See below

>>> Maybe we can call it  "stuff" ?

>
>

>>> Without properties it cannot be identified :-)

>

>> It depends how we define a property. I my opinion a property is a
>> characteristic that is NOT intended to identify entities. Rather it is
>> intended to describe them semantically (how an entity looks like among
>> other entities).
>>
>>           thing
>>         /   |   \
>> entity identity dimension
>>
>> - entity has some identifier
>> - identifiers refer to some entity
>> (entities and identities live in pairs)
>>
>> - dimension can be applied to both entities and identities because both
>> these things have a structure (fields, columns etc.)

>
> How an identifier look like ?
> Are you talking about the names or about the true names ?

They are described just as entities, i.e., as a combination of some field values. The difference however is fundamental: there is a world of identifiers and the world of entities (the things that are being identified). Here is a short list of their properties:

• When we use/model entities we do not see identifiers because they are at lower level. When we use/model identifiers we do not care what kind of entity they will represent.
• Identifiers are traveling things. They do not have a constant position and can be passed between entities. In contrast, entities have a constant position that cannot be changed.
• Identifiers are passed by value, while entities are passed by reference (by means of identifiers).
• We never what an entity is in reality because it is always represented indirectly via its identifier. Identifiers are given by themselves so we can touch them or do whatever we like.
• Their life-cycle is different. Entities are created once and then exist until deleted. Identifiers are created each time we need to pass them.
• Formally, identifier are combined with AND connective. Entities are combined with OR connective.
• Properties of entities are intended to characterize it semantically (meaningfully) using other entities. Properties of identifiers are intended to provide a unique representation and means of access to the underlying entity (it should not be used for semantic characterization because one type of identifier can be used for many different types of entities not known in advance).

We can use other terms for them (say, object and reference) however I think this list confirms that these notions deserve different terms which have to be dealt separately. The term thing (or stuff) would be then used for both simultaneously.

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Received on Fri Feb 24 2006 - 05:01:06 CST