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Hi,
I am trying to figure out under what circumstances I should use weak (non-identifying) relationships (where the primary key of the related entity does not contain a primary key component of the parent entity), verses when I should use strong (identifying) relationships (primary key of the related…
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Hi,
I am trying to understand why this statement in the book is wrong: "given a C entity, there is at most one related A entity and at most one related B entity".
Is it that it doesn't apply to a specific kind of relationship??
So, if I have an example of a student who is in attendance to a course…
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I'm using Microsoft SQL Server 2008 Management Studio to create a relational schema by following an Entity-Relationship diagram. (included below; unrelated details removed)
Until now, primary and foreign keys have been working as expected. But when I try to create a foreign key from the entity…
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Hi,
I am implementing a small database(university Project) and i am facing the following problem.
I created a class diagram where i have a class
Train {Id, Name, Details}
And a class
RollingStock
which is than generalized in Locomotive and FreightWagon.
A train is Composed by multiple RollingStock…
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I'd like to improve my understanding of cardinality constraints in ER diagrams.
I have two entities:
User
Location
But, I want the relationship between these two entities to be many-to-many (a user can be in many locations and a location can have many users).
To do this I need to introduce an…
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Most of the problems I have to solve in my job as a developer have to do with data modeling.
For example in a OOP Web Application world I often have to change the data properties that are in a object to meet new requirements.
If I'm lucky I don't even need to programmatically add new "behavior" code…
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You can find many different data modeling resources. It is impossible to list all of them. I selected only the most valuable ones for me, and, of course, the ones I contributed to. Books Chris J. Date: An Introduction to Database Systems – IMO a “must” to understand the relational model…
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I am struggling with a data model (I use MySQL for the database). I am uneasy about what I have come up with. If someone could suggest a better approach, or point me to some reference matter I would appreciate it.
The data would have organizations of many types. I am trying to do a 3 level classification…
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I'm working on an iPhone app and need a little advice on modeling the Core Data schema. My idea is a utility that allows the user to speed-dial their contacts using user-created rules based on the time of day. In other words, I would tell the app that my wife is commuting from 6am to 7am, at work…
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I'm storing some very basic information "data sources" coming into my application. These data sources can be in the form of a document (e.g. PDF, etc.), audio (e.g. MP3, etc.) or video (e.g. AVI, etc.). Say, for example, I am only interested in the filename of the data source. Thus, I have the following…
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