Re: Object-oriented thinking in SQL context?

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Date: Wed, 10 Jun 2009 02:40:52 -0700 (PDT)
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On 9 juin, 23:57, rp_at_raampje.(none) (Reinier Post) wrote:
> >> I am not aware of any precisely and consensually OO defined concept.
> >> I have asked hundreds of OO programmers in the past about a definition
> >> about what an object and each of them came with a totally different
> >> definition.
> But it's pretty much clear what a UML class diagram is, isn't it.
Nope. I do not use UML concepts at all in my daily life.

> >You are a database desinger, right? Do you ever use the
> >'entity-relation' method when you design a database?
> >If so, what is an 'entity'?
> The entity-relationship method is often used, advocated and taught
> for the design of databases.  The design starts by creating
> an entity-relationship diagram, that is systematically transformed
> and provided with implementation detail until an ER diagram results
> that specifies a relational database schema.
> An ER diagram is a representation of the relations (tables)
> and foreign key relationships in a relational database schema.
> The relations in the schema are the entities and many-to-many
> relationships in the ER diagram; the foreign keys are the
> one-to-many relationships and the links between many-to-many
> relathipships and entities in the ER diagram.  Every ER diagram
> can be created out of a relational schema in this way, but not
> every relational schema corresponds to an ER diagram; certain
> limitations on the structure of the structure of the foreign keys
> apply.
> Entity-relationship diagrams and UML class diagrams are very closely
> related.  The entity sets in an ER diagram correspond to the classes
> of an ER diagram; the relationship sets to associations.
> There are also many differences, but the starting point is the same.
Thanks for the explanations. In a past life, I used visual representations and diagrams to represent relations, functionnal dependencies or required components of a data model but I came to the conclusion that a textual representation was more effective into representing logical aspects of a model. I now mainly use one tool for database design: notepad.

> [...]
> >> > 1) If OO concepts can be handled at all in SQL databases.
> >> > 2) If so, how it is done.
> Well, sometimes you have 'data' classes that do little but
> define a bunch of properties with simple values, and you create
> and manipulate collections of such objects; such classes and
> collections are a quite like database tables.  Inheritance
> is also a very useful notion in database design, if we apply
> it to properties (attributes, columns) only.  But nothing
> corresponds to the notion of method.  Methods invite
> class-specific, object-by-object manipulation techniques;
> SQL on the other hand is essentially a language that maps
> tables to tables with operations such as row selection,
> column selection (projection), union, and join.  You don't
> manipulate or navigate iundividual values and rows, databases
> weren't designed for that.
Databases are meant to be used to manipulate sets of values. Saying that databases weren't designed for that seems a hasty conclusion.

> >> > I ask the same question: How is SQL different and similar
> >> > to what I already know.
> >> In ways you can not tell if you do not go through a self learning
> >> process of education in database concepts.  If you believe this is not
> >> necessary and OO concepts are sufficient to understand database theory
> >> then it will be difficult to help you.
> Some people in this newsgroup believe that the relational model
> is sacred, its inventor Codd was a holy man, and a guy called Date
> who has written a bunch of popular books on the subject is his
> replacement on earth.  Anything you say to suggest that other people have
> something intelligent to contribute on the subject, or have already done
> so, perhaps using slightly different ideas or terminology, is met with
> the scorn only dogmatists can muster.  
What may appear as dogmatism by a minority is in fact a counter balance reaction to the indignified promotion of ignorance done by some others. There is no dogmatism into encouraging people to do some reading.

> Pay attention to their ideas,
> ignore their attitude.
Would the *dogmatic* people have some interesting things to say ?


> Not only newbies, anyone with different ideas or different terminology.
> This problem is hard to avoid in human communication, but it seems
> particularly bad in computer science.
The communication is bad because of the ignorance of most computer science practitionners. For most of them, a limited grasp of computer science concepts helps making a living, which I respect. But a small minority of self promoted morons uses the ignorance of the majority to promote further ignorance.

Anybody serious scientist would tell you that the*serious* basis science communication is understanding first how fundamental theory works to be able to relate to common fundamental concepts with larger audiences. Received on Wed Jun 10 2009 - 11:40:52 CEST

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