Talk:Conceptual schema

message: Ok, I completely re-vamped this definition, in conjunction with those for logical and physical models DavidCHay 17:54, 13 March 2007 (UTC)
thread_title: General Edits

message: I’ve been reading some of the database publications here on Wikipedia and I have come across an error in ambiguity. I will talk in the context of this page for ease, but some other pages have this problem too.
The "conceptual level" as used by this whole article implies that it is created using semantic or conceptual (i.e., it uses relationships, entities, etc.) modeling of data and thus it reads as if this level doesn’t really exists per se (that is, it is not defined within the database).The problem that I am having is that famous data base author, C.J. Date, clearly states that the conceptual level is a community view (the article got this right) of the whole database, but furthermore, that it is defined with the means of a conceptual schema that is written using a conceptual DDL (data definition language).
The “conceptual level” as used in the articles implies that it is created using semantic modeling, but there is no DDL for semantic modeling, as there is no such formal thing as semantic model of data (as Date explains in chapter 14 of [1]). Data actually says, and I quote “The conceptual level will definitely be relational, in the sense that the objects visible at that level will be relational tables and the operators will be relational operators” (Page 36 Chapter 2 of [1]). Not only this, but Date is very clear in that there will be a mapping between the internal level and the conceptual level (Page 41 Chapter 2 of [1]). Thus, the conceptual view of things must exist (how could we map it if it is not defined), and the conceptual modeling (or semantic modeling) does not permit this. It does indeed permit an easy way to achieve a good database design, but from there you have to use normalization and other tools to create the conceptual schema. 
This proves how bad the opening sentence of this article is: “conceptual schema or conceptual data model is a map of concepts and their relationships.” First of all, the conceptual schema is a data model in the sense that it talks about how information is organized in the database. But using conceptual data model as means to describe a synonym for the conceptual schema is very confusing, for we can also talk about data models as in the relational model of data, which is a data model. As defined by Date “A data model is an abstract, self-contained, logical definition of the objects, operators, and so forth, that together constitute the abstract machine with which users interact. The objects allow us to model the structure of data. The operators allow us to model its behavior” (page 15, chapter 1 of [1]). In this sense, the conceptual schema is NOT a data model. Indeed, the conceptual schema is defined by a DLL which follows SOME data model. 
The second part of my quote of the article “..is a map of concepts and their relationships” is also terribly misleading. The relational model of data was created by Cobb using semantic modeling ideas (Chapter 14, page 425 of [1]), but the relational model of data has little to say about the relationships between relations (using this latter term to mean table, loosely speaking). These realtionships are ideas that we use to design the database, but tables as they are imply no relationships. Yes, we have for example JOIN operations that seem to perform relationship operations implied in semantic modeling, but these join operations are really set level operations that could well be described (and more effectively so) without the use of relationships. 
It goes without saying then, that the whole article is very ambiguous. Look at another quote: "Because a conceptual schema represents the semantics of an organization, and not a database design, it may exist on various levels of abstraction." This is actually dead wrong, unless there is another definition for conceptual schema. Still, Date's definition goes as: "the conceptual view is defined by means of the conceptual schema, which includes definitions of each of the various conceptual record types. The conceptual schema is written using another data definition language, the conceptual DDL. If physical independence is to be achieved, then those conceptual DDL definitions must not involve any considerations of physical representation or access technique at all--they must be definitions of information content only" (Chapter 1, page 40 of [1]).
The difference between base relvars and views might shed some more light into the difference between conceptual and external levels, but they share one thing in common: it is imperative to understand that views might help defining an external schema, but that view was defined over a base relvar, probably a conceptual level object. See Chapter 4 of [10].
I hope I could get the point across, I am an Ecuadorian living in Ecuador (I don’t get to practice my English that often), and so my English might be rusty. 
[1] C.J. Date. An Introduction to Database Systems, eighth edition. Addison Wesley (2003). 
Freakycreator (talk) 08:04, 10 November 2010 (UTC)
thread_title: Use of word "conceptual" ambiguous

message: * This edit is copy/pasted here from the data structure diagram article. -- Mdd (talk) 22:09, 16 October 2009 (UTC)
thread_title:  Copy-paste registration 

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thread_title:  External links modified 

message: cognitive science, Schema_(psychology) - cf. the latter link on "Schema", how can I make the underscore disappear? Thy--2A02:1811:5075:B00:D8F6:B7E8:90EC:DBD1 (talk) 20:07, 8 November 2019 (UTC)
thread_title:  We need to pub more links to schema used in other contexts like in cognitive sciences