I want to clarify my diagram that I have created;
ER diagram
I was wondering what I have made means the following things;
- A company can book multiples jobs
- A company MUST own a job for it to exist
Am I correct in those assumptions from my diagram or have I done something wrong?
Related
I have a question regarding ER diagram
The question is how do we connect entities in an ER diagram
the options are
1. foreign key
2. relationship
3. primarykey
4. association
I know if the question was about relational diagram the answer will be: FK, but as I recall there is no FK in ER diagram and the book says the right answer is 1, so any help?
1.Several students from different departments may participate one project. Each project has at least one student member.
2.Each student may or may not participate the projects, but one student can participate several projects at the same time.
In 1st statement, the relationship of student and project is M-1. But in the 2nd statement, the relationship of student and project is 1-M
If I want to express their relationship in a single ER digram, should I use the M-1 or 1-M? Or is my ER diagram wrong?
ER Relation
I am an ICS student and I have been given two questions.
1.) List all the Functional Dependencies that hold for the database.
2.) For each relation in your relational schema write down whether the relation is in BCNF or 3NF and if not give a violating FD.
I'm just having problems understanding the relationship between functional dependencies and the ER Diagram. I've watched a few videos online but I'm still getting stuck on how to answer the two above questions and would appreciate some help in finding the right direction.
Below is an ER diagram and I was hoping someone could give some examples on how to start from here.
For each entity set (e.g. Department), each attribute is an FD (e.g. Department Name -> Location).
For each relationship set (e.g. Offers), there's an FD from the combination of keys of "many" entities to each of the keys of "one" entities (e.g. Course_ID -> Department Name)
all the attributes include in ER diagram or not?
My database have 8 tables and nearly 50 attributes, i include these 50 attributes in a single diagram OR not?
First thing - ER diagram is something that is first created usually and then later on converted into a data model like relational. So the data storing requirements are modeled into an ER diagram first and later on are converted into tables. There is rarely a case where you have to reverse engineer an existing data model into the ER diagram level (Conceptual Level).
During this process, tables are created for enitities and relationships accordingly (using some algorithmic process).
And a good way of practice is to draw the ER diagram with only entities and relationships without the attributes as it makes it very clumsy and difficult to concentrate on the actual entities and the relationships between them. Later on in a separate document or a page, you can list all the attributes corresponding to entities individually.
Hope this gives you a basic idea.
I am trying to understand this diagram and after reading over PowerPoints and the Book I still don't see an answer to my question.
What is the difference between the single line and the double line connecting the relationship to the entities? Thank you.
It signifies total participation of Movie in Acts_In. Also known as existence dependency.