Re: At what ANSI/SPARC level are you, when creating new... totally lost
Date: Sat, 14 Jul 2007 08:20:43 -0700
Message-ID: <1184426443.806745.38420_at_k79g2000hse.googlegroups.com>
hello
This is really confusing
>>Thus, by creating a new database are you creating logical model or
But the quote below suggest that logical model is part of internal
schema and thus conceptual model can't also be logical model?!
>>
>>conceptual model?
>
>The external model and the conceptual model are both logical models.
>>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