I need help with a project for my university programme. The task is to design a database using MySQL and creating ER- and EER-Diagrams for it. The database I want to create is my music library.
My main entities will be Song, Artist, Album and Publisher. Since one Song can have multiple arists, how do I represent that in my design/diagram? My understanding is that that attribute can usually have only a single value.
I hope you can help me with this.
ERD Solution
So you actually have a many-to-many relationship because a song can be sung by many artist and an artist can sing many songs. Therefore, you need a junction table to represent a many-to-many relationship in an ERD.
Related
I'm working on a database project about music and albums in MySQL, where i make a list over some popular artists, their most sold album, and the songs contained within them. But i suddenly got really uncertain of what to do when it comes to filling in the name of the songs for each album. Should i make an individual table for each list of songs, or should all the songs (about 50 of them in total from all the albums) from all the different artists (5 different artists) be filled inn in the same table (i'm eventually gonna export the data and connect it to a PHP folder
Hope the question was clear
All the songs should be in one "Songs" table. Then you create a column "Album ID" in that table which is a foreign key back to the ID column in the albums table. This is how you know which song belongs to which album. (And of course you have the same kind of relationship between "album" and "artist".)
This is called a "one-to-many" relationship and is one of the basic principles of relational database design.
If you ever find yourself creating multiple tables to represent the same kind of data item, you know you've gone wrong.
N.B. If you want to support the idea that the same song (or track probably, to be more accurate, since many different recordings of a song could potentially be made) can be included on multiple albums, then you'll need to implement a "many-to-many" relationship where you have an extra table in between "albums" and "songs" which holds Album ID and Song ID. Each would be a foreign key back to the Albums and Songs tables, respectively. And to ensure no duplication, both fields would be specified as a Compound Primary Key. That way you can list the same Song ID in that table many times against different albums. Same again if you want to have that flexibility in the relationship between "artists" and "albums".
This might be a good time to take a break and study relational database design and data normalisation concepts in some more detail, then you can start to see these patterns for yourself and make the right decision in your schema designs.
Similarly to this question about databases for playlists you should also use one table for the albums and one table for the songs.
Additionally you might also need a table for artists, etc.
I'm working for a database project that my professor gave to me and now i'm designing the relational schema of database.
I have three entity types album, photo and video that means an album can contain both of them, but I have no idea how to tie them up together.
I'm a beginner in this field so please give me some advice what to do ?
I assume an album can contain several photos and videos. You can create a table joining them. This table can have essentially fours columns: the id of the album, the id of the photo or video, a flag distinguishing whether photo or video, and an index to define the order of the items within an album.
It can of course have an own ID (drawn from a sequence or via autoincrement), a timestamp when it was created, a userid by whom etc.
Can several copies of the same photo belong to an album?
I am trying to think of the best design for trainers and clients database.
My initial thought was this:
Entity person with common attributes of clients and trainers (name, dob, etc.). A client can have only one trainer. One trainer can have many clients.
I wonder whether creating an entity user for controlling clients and trainers privileges, or just adding an attribute Role in person
Another thing I had considered was having everything in a single entity with a recursive relationship?
Any suggestion?
Thanks.
Trainers and Clients from an entity perspective probably have different data that you care to track about each one. You can still have a global users table, but the trainer and client should have a 1:1 relationship with the user entity. You can then have a join table between clients and trainers. I would suggest a many to many relationship here, just in case someone really wants to get in shape and wants to have 2 trainers.
Can trainers have trainers? For example, a trainer who specializes in triathletes might be a weak swimmer and have a swim coach.
I like the Role design myself.
I am building a music streaming site, where users will be able to purchase and stream mp3's. I have a subset entity diagram which can be described as follows:
I want to normalise the data to 3NF. How many tables would I need? obviously I want to avoid including partial dependancies, which would require more tables than just album, artist, songs - but I'm not sure what else to add? Any thoughts from experience?
Well, you've done the ER level. You need to identify Keys and Attributes before you can work out Functional Dependencies. There is a fair amount of work to do before you get to 3NF. Eg. Song Titles are duplicated.
Also, there are questions:
is the site selling Albums, Songs, or both ? (I've modelled both)
if both, how do you track a sale or download ?
do you care about the same Song title recorded by different Artists ?
Anyway, here is a resolved ▶Entity Relation Diagram◀, at least for the info provided. It is closer to 5NF than 3NF, but I cannot declare it as such, because it is not complete.
Readers who are unfamiliar with the Standard for Modelling Relational Databases may find ▶IDEF1X Notational◀ useful.
It uses a simple Supertype-Subtype structure, the Principle of Orthogonal Design. The Item that is sold ie either an Album xor a Song.
Feel free to ask clarifying questions.
You will need 4 tables: Artists, Songs, Albums, and AlbumSongs.
The last one is required since the exact same song (=same edit/version...) could be included in several albums, so you have there a m-to-m relationship.
I agree with iDevelop but with 1 extra table. Here is how I would model it.
Tables: Artist, Song, Album, AlbumSongMap, SingleInfo
If the song was a released as a single on a different date, you can get that from SingleInfo. The single may have been released with some cover art that is different from the album art. You would store the singles art in SingleInfo. MAYBE a song can be released as a single multiple times, with new cover art or something so it could possibly be a 1-many relation. Otherwise it is 1-1.
If you can join Song with SingleInfo that means it was released as a single. If you can join Song with Album (using the map) then you will find all the album's it was released under.
A digital enhancement to an old song is a new song. (or at least a different binary). You may want to further normalize Song to allow storage of digital enhancements without duplicating songName, etc.
When you switch over from ER modeling to relational modeling (tables), you need one table for each entity. You also need a table for some relationships.
In the diagram you've given us, both relationships are many to one. Many to one relationships do not require a table. You can get away with adding foreign keys to entity tables. Therefore the answer to your question is 3 tables: Artists, Albums and Songs.
However, I question your ER diagram. It seems to me that the "contains" relationship is really many to many. An album clearly contains many songs. But a given song can appear on more than one album. So there should be an arrowhead on the line that connects "contains" to "album".
If you accept this revision to your ER model, then the number of tables increases to 4: Artists, Albums, Songs, and Contains.
A similar argument might be made for Artist and Song. If two artists collaborate on a single song, (e.g. Dolly Parton and Kenny Rogers singing "Islands in the Stream" together,
then you might want to model "produces" as a many to many relationship. Now you need 5 tables: Artists, Albums, Songs, Contains and Produces.
Artists, Albums, and Songs are going to require a PK that identifies the corresponding entity. Entity integrity demands that the correspondence bewteen entity instances and table rows be one-to-one.
The Contains and Produces tables can be built without a separate Id attibute. You will need a pair of FKs in each of these tables, and you can declare a compound PK for each table consisting of the two FKs.
Referential integrity demands that you enforce the validity of FK references, either in your programs or by declaring a references constraint in the DB. I strongly prefer declaring the constraint in the DB.
There are couples of questions around asking for difference / explanation on identifying and non-identifying relationship in relationship database.
My question is, can you think of a simpler term for these jargons? I understand that technical terms have to be specific and unambiguous though. But having an 'alternative name' might help students relate more easily to the concept behind.
We actually want to use a more layman term in our own database modeling tool, so that first-time users without much computer science background could learn faster.
cheers!
I often see child table or dependent table used as a lay term. You could use either of those terms for a table with an identifying relationship
Then say a referencing table is a table with a non-identifying relationship.
For example, PhoneNumbers is a child of Users, because a phone number has an identifying relationship with its user (i.e. the primary key of PhoneNumbers includes a foreign key to the primary key of Users).
Whereas the Users table has a state column that is a foreign key to the States table, making it a non-identifying relationship. So you could say Users references States, but is not a child of it per se.
I think belongs to would be a good name for the identifying relationship.
A "weak entity type" does not have its own key, just a "partial key", so each entity instance of this weak entity type has to belong to some other entity instance so it can be identified, and this is an "identifying relationship". For example, a landlord could have a database with apartments and rooms. A room can be called kitchen or bathroom, and while that name is unique within an apartment, there will be many rooms in the database with the name kitchen, so it is just a partial key. To uniquely identify a room in the database, you need to say that it is the kitchen in this particular apartment. In other words, the rooms belong to apartments.
I'm going to recommend the term "weak entity" from ER modeling.
Some modelers conceptualize the subject matter as being made up of entities and relationships among entities. This gives rise to Entity-Relationship Modeling (ER Modeling). An attribute can be tied to an entity or a relationship, and values stored in the database are instances of attributes.
If you do ER modeling, there is a kind of entity called a "weak entity". Part of the identity of a weak entity is the identity of a stronger entity, to which the weak one belongs.
An example might be an order in an order processing system. Orders are made up of line items, and each line item contains a product-id, a unit-price, and a quantity. But line items don't have an identifying number across all orders. Instead, a line item is identified by {item number, order number}. In other words, a line item can't exist unless it's part of exactly one order. Item number 1 is the first item in whatever order it belongs to, but you need both numbers to identify an item.
It's easy to turn an ER model into a relational model. It's also easy for people who are experts in the data but know nothing about databases to get used to an ER model of the data they understand.
There are other modelers who argue vehemently against the need for ER modeling. I'm not one of them.
Nothing, absolutely nothing in the kind of modeling where one encounters things such as "relationships" (ER, I presume) is "technical", "precise" or "unambiguous". Nor can it be.
A) ER modeling is always and by necessity informal, because it can never be sufficient to capture/express the entire definition of a database.
B) There are so many different ER dialects out there that it is just impossible for all of them to use exactly the same terms with exactly the same meaning. Recently, I even discovered that some UK university that teaches ER modeling, uses the term "entity subtype" for the very same thing that I always used to name "entity supertype", and vice-versa !
One could use connection.
You have Connection between two tables, where the IDs are the same.
That type of thing.
how about
Association
Link
Correlation