The following is a sample logical model created using Oracle SQL Developer Data Modeler:
After engineering the model to a relational model, the resulting model is the following:
Is the above model considered to be a Physical Model? I believe this is a physical model, but the fact that it's called a relational model is making me have doubts.
From 1keydata:
Physical data model represents how the model will be built in the database. A physical database model shows all table structures, including column name, column data type, column constraints, primary key, foreign key, and relationships between tables.
What you have there represents what needs to be implemented in your database.
The relational model is "an approach to managing data using a structure and language consistent with first-order predicate logic" [Wikipedia]. In high level both diagrams follow the relational model.
Related
I have tried looking for a entity relationship model using the schema of distributed database but I found diagrams as it:
or I found entity relationship models but they are not using the schema of distributed database like this...
I did next diagram but teacher said me it is not using the Distributed database schema. How can i convert it to istributed database schema??
When I convert Physical Data Model to Access Database using Power Designer I don't see the relationships in the access database, only the tables, why?
I'm creating a new visual studio web site using MVC4/webapi that will go against a database of 75 preexisting tables (not perfect in terms of foreign keys, etc.). I'm thinking that I will create an ado.net entity data model and select all my tables. then, when my tables change I will do the "update model".
With my linq2sql projects, I always ran sqlmetal against all my tables all the time to keep things in sync and that worked fairly well.
Is my plan to have all my tables in one ado.net entity data model reasonable? what pitfalls might I run into? Is it better to have lots of ado.net entity data models? I've tried having multiple ado.net entity models in other projects and I seem to constantly be getting my connection strings doubled in my web.config.
I did do a search on SO and did not find any discussions that directly addressed my concern.
If you followed your plan, you would miss out on an opportunity to have an entity model simpler than your database model:
Your application almost certainly doesn't need all 75 tables.
You would be missing the opportunity to consider a series of 1-1 tables as a single entity
You would be missing the opportunity to use inheritance in your model
You would be missing the opportunity to keep junction tables out of your model
You would be losing one of the greatest advantages of Entity Framework over LINQ to SQL: it does not need to stay one-to-one with the database.
I've created the Entity-relationship model of my database and the I normalized it, but I've a issue, I don't know if after of the normalization I've to create new relations between news tables derived from normalization and the original tables or not.
When you say "relations", you mean constraints, correct? :-) Normalizing a relational database means you broke the tables up to reduce redundancy and dependency. If you are making more tables, then yes you need to create new constraints (keys). You'll also need to run a conversion on your database to move the data to the new tables appropriately.
I was reading about ORMs and one of the descriptions I read said that the ORM interacts with database metadata.
Why is this important or relevant?
Metadata, as I understand, is just a way of describing what the database contains. So, for example, the database might have an internal table that lists what user tables have been created. Why would something like this be useful to an ORM?
What this means is that the ORM maps the schema, or structure, of the database to objects. Typically, this means mapping tables to classes (User table to User class), fields to attributes (Age field to User.Age attribute), and each record then represents an instance of that object.
The ORM uses the metadata to generate the code used to access the tables. For example, if it's a date column then it generates the code to deal with that column as a date.
It will read foreign keys and primary keys to build relationships in the code as well as for generating the proper SQL syntax.
This is just a few of the ways it uses the metadata.