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  1. #1
    Join Date
    Dec 2004
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    7

    Help (Relational & E-R model)

    Hi guys...I'm new here.Nice to meet you all
    So,i've just started a lesson in the university i'm studying which called database systems. I have an exersise to do for relational & e-r model. I need your opinions (cause as i can see it's not something fixed)for some questions.

    1)Which is the strongest spots of each model?
    2)Is there any weak spot in each one?If yes, which one (maybe more than one)?
    3)Try to imagine a model which concludes(completely or partly) both models.Does this make sense?If yes,what could it be this super-model?

    I would appreciate very much if you could answer me these questions.
    Thanks in advance!
    Last edited by MPSP; 12-12-04 at 19:40.

  2. #2
    Join Date
    Apr 2002
    Location
    Toronto, Canada
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    1)Which is the strongest spots of each model?

    relational model and e-r model are apples and oranges

    the relational model's main strength is that it is based on math

    the e-r model's main strength is that it is visual


    2)Is there any weak spot in each one?If yes, which one (maybe more than one)?

    relational model has no weaknesses -- some people will argue this point, but they are wrong!!!

    e-r model's main weakness is that it does not always mean you get a good database out of the design effort


    3)Try to imagine a model which concludes(completely or partly) both models.Does this make sense?If yes,what could it be this super-model?

    this doesn't make sense
    rudy.ca | @rudydotca
    Buy my SitePoint book: Simply SQL

  3. #3
    Join Date
    Dec 2004
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    7
    First of all thanks for answering.

    -Can you please explain what do you mean when you say apples and oranges?
    -Why it doesn't make sense (the super model)?Can you tell me some more things about that?
    -And what do you mean by "out of the design effort"?

    Sorry for all these questions but i'm completely new!
    I hope i'll get an answer.

    Tnx again.
    Last edited by MPSP; 12-12-04 at 14:52.

  4. #4
    Join Date
    Oct 2002
    Location
    Baghdad, Iraq
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    697
    Quote Originally Posted by r937
    relational model has no weaknesses -- some people will argue this point, but they are wrong!!!
    Would you settle for no *instrinsic* weaknesses?

    Quote Originally Posted by MPSP
    -Can you please explain what do you mean when you say apples and oranges?
    First off, it's not true. You *can* compare apples and oranges.

    As to what it means... Say you're a judge whose job is to determine who has the best produce. If you choose some apples from Farmer Abe and some oranges from Farmer Bob your results won't make sense because the taste is fundamentally different.

  5. #5
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    Oct 2002
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    Quote Originally Posted by MPSP
    3)Try to imagine a model which concludes(completely or partly) both models.Does this make sense?If yes,what could it be this super-model?
    Since everything you can do with the E-R model can be accomplished relationally, the relational model would be your super model.

    If I were designing a toolset to do relational modelling, I would want to allow the user to use different strategies to draft his schema. In this case, the E-R model's structures would be defined relationally and you could use simple macro replacement to build the logically correct relational expressions.

    If the user were a scientific user doing Matlab-type work, I would also want the vectors, matrices &c. to be defined relationally.

    Thus, a vector variable v might be backed by a relational variable rv that has constraints on it that it have a PK column Offset and a column of arbitrary data Values. Vector operations would then be translated into the appropriate relational operations.

    What's important is that it would all be application independent: having designed your structures in your Matlab-type program, you could browse them with a spreadsheet, and all the various apps could share the DBMS with stepping on each other's toes.

  6. #6
    Join Date
    Apr 2002
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    Quote Originally Posted by MPSP
    -Can you please explain what do you mean when you say apples and oranges?
    the relational model is not comparable to ER models
    The relational model for management of a database is a data model based on predicate logic and set theory.

    The fundamental assumption of the relational model is that all data is represented as mathematical relations, i.e., a subset of the Cartesian product of n sets. In the mathematical model, reasoning about such data is done in two-valued predicate logic (that is, without NULLs), meaning there are two possible evaluations for each proposition: either true or false. Data is operated upon by means of a relational calculus and algebra.
    -- Relational model
    the ER (entity-relationship) model, on the other hand, is a way of drawing a diagram to show entities and their relationships
    rudy.ca | @rudydotca
    Buy my SitePoint book: Simply SQL

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