Talk:Logical data model
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Merge Logical schema and Semantic data model here
- I guess this isn't a good idea after all. -- Marcel Douwe Dekker (talk) 22:26, 27 November 2008 (UTC)
Remove references to XML
The claim that "Currently, the choices [of a logical schema] are relational, object-oriented, and XML" is incorrect. XML is a coding method rather than a type of schema. Any type of logical schema could be represented in XML. I will reword this section soon unless people comment here about why I shouldn't. Matthew C. Clarke 03:41, 31 October 2009 (UTC)
- I've now done this Matthew C. Clarke 21:41, 4 November 2009 (UTC)
Dependant or independant from data management technology ?
The article recently moves from
"A logical data model (LDM) in systems engineering is a representation of an organization's data, organized in terms of a particular data management technology."
"A logical data model (LDM) in systems engineering is a representation of an organization's data, organized in terms entities and relationships and is independent of any particular data management technology."
Why ? Does it mean that the LDM representation should stay the same for a relational database, a OLAP cube or an XML file/stream,... ? I'm not sure.
I have, at the moment, a lot of disucussions around this topic and everyone seems to have a different opinion. What are yours ?
Yes, the CDM and LDM are independent of any particular data management technology, such as Oracle or MySql database table schema. That is why the Physical DM is different, to provide the data management-specific info, like field format and index-key identification. — Preceding unsigned comment added by Kitdaddio (talk • contribs) 15:25, 20 March 2013 (UTC)
- I think the statement is unclear and confuses "specific data mangement technology" with "specific data management product". The technology might be RDBMS, object databases, XML files, etc. The product can be Oracle, MySql, etc. The following quotes are from articles that all agree on the difference between conceptual and logical data models:
Logical Data Models (LDMs) : describes the semantics, as represented by a particular data manipulation technology. This consists of descriptions of tables and columns, object oriented classes, and XML tags, among other things.—Unknown, https://en.wikipedia.org/wiki/Data_model
A logical schema is a data model of a specific problem domain expressed in terms of a particular data management technology. Without being specific to a particular database management product, it is in terms of either relational tables and columns, object-oriented classes, or XML tags.
Logical schema: describes the structure of some domain of information. This consists of descriptions of (for example) tables, columns, object-oriented classes, and XML tags.
- The current article states different things, both which I think are unclear or wrong:
a logical data model (LDM) is a representation of an organization's data, organized in terms of entities and relationships and is independent of any particular data management technology
Even so, since the logical data model anticipates implementation on a specific computing system, the content of the logical data model is adjusted to achieve certain efficiencies.
- I think the other articles are correct and that the change made is incorrect. This error is also reflected in https://en.wikipedia.org/wiki/Entity%E2%80%93relationship_model which, unclearly/erroneously states "The logical ER model is however developed independent of technology into which it will be implemented.".
- My suggestions:
a logical data model (LDM) is a representation of an organization's data dependent on the type of data management technology (RDBMS, object database, etc.), but independent of any particular vendor's data management product
Even so, since the logical data model anticipates a certain type of data mangement technology, the content of the logical data model is adjusted to reflect that and to achieve certain efficiencies using.
- Do you agree?
Conceptual v Logical v Physical
Logical data models are typically developed for a specific application (e.g. Sales system, data warehouse), though the technology has not been chosen. For the former, operational system, you would normalise (typically to 4NF), but the BI manager would have screaming hab-dabs if you proposed anything other than a star schema for the data warehouse. As the logical model contains primary & secondary keys and relationships, surely you would also produce the logical model as either 4NF or star schema as appropriate the the business use of the application? MaryEFreeman (talk)