Re: At what ANSI/SPARC level are you, when creating new... totally lost

hello

This is really confusing

>>Thus, by creating a new database are you creating logical model or
>>conceptual model?
>
>The external model and the conceptual model are both logical models.

But the quote below suggest that logical model is part of internal schema and thus conceptual model can't also be logical model?!

>>
>>An internal schema is an organization of data according to the technology >>being used to record it. This includes the terms for components recognized by >>each kind of data manipulation technology: relational database management >>system (DBMS) "tables," hierarchical DBMS "segments," object "classes," >>etc.It also includes the terms for the internal physical storage of data on the >>computer (cylinder, track, etc.). In the past, the DBMS terms have comprised >>the logical schema, and the physical storage terms have comprised the >>physical schema. The internal schema is really two: the logical schema which >>represents data in terms appropriate to a particular data manipulation approach >>as usually expressed in a database management system or DBMS (the >>"designer's view") and the internal schema which is concerned with the physical >>characteristics of storage on a storage device ("builder's view").Internal schema >>( and thus logical schema ) is at level three of the ANSI / SPARC architecture.”
>>

Since I only know ( a little ) about relational database, I’m going to ask the following question in the context of relational database:

The way I understand the above paragraph is that logical schema ( which the article claims is a part of internal schema ) deals with tables, while conceptual level deals with objects ( entities ) and thus knows nothing about tables and keys. Uh, what am I missing here?!

Even wikipedia ( again, to my understanding ) puts Logical schema inside level three ( inside internal schema )  In other words, article implicitly suggest that conceptual model doesn’t deal with tables etc:

>>A Logical Schema is a data model of a specific problem domain that is in terms >>of a particular data management technology. Without being specific to a >>particula database management product, it is in terms of either (for example, in >>2007) relational tables and columns, object-oriented classes, or XML tags. This >>is as opposed to a conceptual data model, which describes the semantics of >>an organization without reference to technology, or a physical data model, >>which describes the particular physical mechanisms used to capture data in a >>storage medium.
>>The next step in creating a database, after the logical schema is produced, is >>to create the physical schema.

> > 3)
> > What is the difference between model and scheme?
>
> These terms are in this context usually used synonymously.
>
> -- Jan Hidders

And what is the difference between the two when used in some other database context ?

thank you Received on Sat Jul 14 2007 - 17:20:43 CEST