You set up a database company, ArtBase, that builds a product for art galleries. The core of this product is a database with a schema
that captures all the information that galleries need to maintain.
Galleries keep information about artists, their names (which are
unique), birthplaces, age, and style of art.
For each piece of artwork, the artist, the year it was made, its
unique title, its type of art (e.g., painting, lithograph, sculpture,
photograph), and its price must be stored.
Pieces of artwork are also classified into groups of various kinds,
for example, portraits, still lifes, works by Picasso, or works of the
19th century; a given piece may belong to more than one group. Each
group is identified by a name (like those just given) that describes
the group.
Finally, galleries keep information about customers. For each
customer, galleries keep that person’s unique name, address, total
amount of dollars spent in the gallery (very important!), and the
artists and groups of art that the customer tends to like.
Draw the ER diagram for the database.
Is the following ERD correct?
Is it possible that a group has zero Artworks?
Is it possible that the Artist didn't produce any artwork but still sits in the database?
1) You used ID as a PK in Artist and Artwork. This is a good thing as the use of an unique name (as requested in the business model) is wrong: after all, two pieces of art or two artists may bear the same name. However, you did respect the business model for the Customer entity whose PK is Name.
You can choose to make a good ERD and use ID as a surrogate PK for Artwork, Artist, and Customer; or respect the business model you were given and use Name as a PK for these three entities. Personally, I'd go with the former.
The following two questions can't be answered given the business model only; the answers below reflect the cardinality in the specific ERD you designed.
2) Yes, because according to the ERD a Group includes from 0 to N Artworks;
3) Yes, because according to the ERD although an Artist makes from 1 to N Artworks (and therefore there wouldn't be the need to insert an Artist in the database if he didn't do any Artwork) there is still a relationship between Customer and Artist in the sense that a Customer likes from 1 to N Artists.
Therefore an Artist can be in the database even if he didn't produce any Artwork (yet), provided that he is liked by at least one Customer. If an Artist didn't do any Artwork and is not liked by any Customer, he won't be in the database.
Missing some context information here, especialy some cadinality information. Pay attention to yourself asking questions about the context:
Is it possible that a group has zero Artworks?
Is it possible that the Artist didn't produce any artwork but still
sits in the database?
This information should be given by you (or by the presenting problem). If this is a work of your course or your college, your instructor needs to better explain the present context. If you are already working as a DBA or data modeler, please look for more information about this problem. It's almost indescribable the importance of a context in the development of an ER-Diagram. Keep this in mind: Without a well-defined context, the problem (the situation) is uncertain, and so is missing information to complete the reflection of a real-world situation. In short:
No complete context, no diagram (without a diagram, there is no system!).
I will make this diagram with you step-by-step, but I'll take some assumptions due to lack of information (context) here. I will give my opinion on certain resources used in ER-Diagram, but that does not mean that I'm saying you're layman. I am just showing my thought, which shows how I learned that here in my country. I believe that you are as capable as I am, ok? Well, let's begin...
Entities in ER-Diagram are defined when we have attributes / properties. According to your description, we can see immediately 3 entities here:
Customers
Artists
Artworks
Relationships exists to express links between entities. The most obvious relationship here is between Artists and Artworks, Don't you agree?
For each piece of artwork, the artist...
In accordance with the context revealed, all artwork has a unique artist (always), but it is uncertain if an artist always has one, multiple, or zero artworks. I SUPPOSE that an artist can have many or no artwork. That being said, we see that artists to artworks have a cardinality 0 to N, because, again, an artist may have made several or no artwork at all.
So far we have defined three entities, and linked two of them. Let's continue...
...its type of art (e.g., painting, lithograph, sculpture, photograph)...
If an artwork has only a single type of art, and an art type is defined only by its name, then we have here what is called a Functional Redundancy (translated from the Portuguese term "Redundância Funcional"). In spit summary, Functional Redundancies are like relationships between two entities, and serve to save you the trouble of repeating the same field in multiple columns in a table (which would be susceptible to errors). In a Conceptual Model, they are represented as a field in an entity with the suffix "(R)" (without the double-quotes).
If an entity has a field (column) like a Functional Redundancy, but with different values (multiple), then we have what is called Multivalued Field (also translated from the Portuguese term "Campo Multivalorado"). These are fields in entities that have the suffix "*" (also without the double-quotes).
This is not the case of the type of artwork, but it would until now for the groups of each artwork:
Pieces of artwork are also classified into groups of various kinds,
for example, portraits, still lifes, works by Picasso, or works of the
19th century; a given piece may belong to more than one group.
This would be true if groups only possess names, and no other entity relate to them. But then you said:
and groups of art that the customer tends to like.
This has changed things a bit. Groups no longer is a Multivalued Field in Artworks entity and becomes an entity with two relationships, one for Customers and one for Artworks. The relationship between Groups and Customers reveals the preferred art groups by customers. The relationship between groups and artworks shows which art groups a artwork is related. Now let's talk about the cardinalities of these relationships.
...a given piece may belong to more than one group. [...]
...and groups of art that the customer tends to like. [...]
Concerning Groups and Artworks, the word "may" says a lot to me. It says that something may or may not be effective. Still, it is uncertain whether an artwork can exist without at least one related group. Because of this, I see a 1 to N relationship from Artworks to Groups.
Conversely, the opposite process is not clear. I believe that there may be groups unrelated to artworks, perhaps because they are new groups created in a given time. So I see a relationship of 0 to N from Groups to Artworks.
Let's talk about Groups and Customers. It seems to me that a customer like at least one group of art. So I see a 1 to N relationship from Customers to Groups.On the opposite side, as already said, it would be possible to add new groups without automatically tying at least one customer to it. I think there may be new groups unrelated to customers. So guess what? We have a relationship of 0 to N from Customers to Groups.
So far we have identified another entity, a Functional Redundancy,
and two relationships with their respective cardinalities. Let's keep going...
and the artists ... that the customer tends to like.
There is a close connection here between two entities, Customers, and Artists. This relationship tells us what artists the customers like. If a customer must like at least one artist, then we have a 1 to N relationship from Customers to Artists. If a customer may or may not like an artist, then we have a relationship 0 to N.
If an artist has zero or more customers who appreciate it, then we have a relationship 0 to N from Artists to Customers. If an artist has at least one client who appreciates it's work, then we have a 1 to N relationship from Artists to Customers.
Lastly...
Galleries keep information about artists, [...] and style of art.
If multiple artists can share a single same art style, then we have a Functional Redundancy here. If several artists have various art styles, then we have a Multivalued Field.
After much talk, I came up with an ER-Diagram presented by your context and assumptions made by me:
NOTE: The green points highlights major assumptions.
Is this right? Is this the correct diagram? The correct answer would be (from me to you):
I do not know...
Without a concrete context, we can not finalize a diagram correctly. My tip is that you finish your context. Only then you will have a correct diagram.
Oh, one more thing. What would be this "money spent" attribute? If customers can buy artworks, it would represent a new relationship between Artworks and Customers. This relationship would represent the purchase of artworks from customers (called "ORDERS", for instance). If not so, skip this paragraph.
If I have forgotten something, please say so. If you have questions feel free to ask, I'm here to help you.
Related
A friend who is a recruiter for software engineers wants me to create an app for him.
He wants to be able to search candidates' CVs based on skills.
As you can imagine, there are potentially hundreds, possibly thousands of skills.
What's the best way to represent the candidate in a table? I am thinking skill_1, skill_2, skill_n, etc, but somewhere out there there is a candidate with more than n skills.
Also, it is possible that more skills will be added to the database in future.
So, what's the best way to represent a candidate's skills?
[Update] for #zohar, here's a rough first pass at teh schema. Any comments?
You need three tables (at least):
One table for candidates, that will contain all the details such as name, contact information, the cv (or a link to it) and all other relevant details.
One table for skills - that will contain the skill name, and perhaps a short description (if that's relevant)
and one table to connect candidates to skills - candidatesToSkills - that will have a 1 to many relationship with both tables - and a primary key that is the combination of the candidate id and the skill id.
This is the relational way of creating a many to many relationship.
As a bonus, you can also add a column for skill level - beginner, intermediate, skilled, expert etc'.
You might also want to add a table for job openings and another table to connect that to the skills table, so that you can easily find the most suitable candidate for the job based on the required skills. (but please note that skills is not the only match needed - other points to match are geographic location, salary expectations, etc'.)
So in my application database I have a business profile entity that has:
one main Category (e.g. Restaurant, Hotel, Hospital, ...etc)
unlimited Subcategories (e.g. pizza restaurant, Italian restaurant, ...etc)
unlimited products (e.g. cheese pizza, pepperoni pizza, ...etc)
unlimited services (e.g. pick-up service, delivery service, ...etc)
P.S. I went with the Restaurant category as an example to demonstration its subcategories/services/products entities, but, it could be any anything really.
First: I can use something like the Adjacency List Model to define unlimited categories and their corresponding subcategories but, what about services and products entities ? how can I link them all to each another knowing that services and products are children of the subcategory entity?
For now this is what I have:
Figure-1
Second: How can I map each Business profile with its Category/subcategories/products/services ?! so that I know each business profile is under what category and what are the subcategories/products/services that each business profile has.
Here is the mapping that I have at the moment:
Figure-2
I am yet a novice database designer, I'm trying to make this database to be as much efficient as possible, as it will receive a lot of traffic. Is what I have now valid as a database scheme or is there any database designing concepts that needs to be dig deeper?
When I read this question I was worried this was going to have a complicated tree structure, but reading your work so far it's very clean and simple.
Personally, I think you're on the right track, and would make a few notes:
It's not hard to link services and products to subcategories, and you can also easily link businesses and products/services. I don't think this needs to be a tree. Just enforce this restriction when the records are created.
Adjacency List Model makes a lot of sense for trees of arbitrary depth for which you need to easily find subtrees, but I'm not sure if that fits your problem, in particular because:
You don't have arbitrary depth. You just have parents and sub-categories.
For something like a business-category system, the number of entries might be low enough that it's not worth adding the extra complexity. It's probably pretty fast to read the entire table and keep it in memory.
If you want services and products linked to both subcategories and categories, the simplest might be to have a single category table and have each category have a parent_id that may be null.
I have these set of requirement:
For each school, the system needs to keep track of its unique name, address, classification (Value could be Elementary, Middle, or High), and number of students studying in it.
For each School System Employee, we need to keep track of the unique employee number, full name, address, salary, and the school where (s)he works. An individual works only in one school.
For each student, we keep track of the student’s name (at times, we need to refer to student’s first name, middle initial, and last name individually), address (at times, we need to refer to the street address, city, state, and zip code individually), the school (s)he attends, and what grade (s)he is in.
The system sends letters to High School students frequently, and hence, needs to keep track of each High School student along with the year when (s)he enrolled in the High School.
A system-wide list of courses offered is kept. Information about a course consists of its unique number, unique title, and number of credits.
For each school, the information about which courses are taught there is kept.
For each student, we keep a grade report that provides the grade (Value could be A, B, C, D, or F) for the student for a specific course.
The School System owns buses which are identified uniquely by their registration numbers. Some students take them to commute between their home and their school, while others use their personal means to commute. We keep track of which student takes which bus to commute. We also keep track of drivers assigned to buses (a driver is a school system employee who could be assigned to multiple buses, and a bus could have multiple drivers assigned to it – consider this a weekly assignment of buses and drivers).
Here is my attempt at the ER design:
This is my first ER design and i just wanted to know if met all the requirements and if I did it correctly? Any help will be much appreciated! Thanks!
First of all I don't like it to omit columns necessary for forein keys, e.g. a school ID in the employee table. But I don't know enough about ER diagrams to say if that would even be allowed.
The diagram looks fine to me. Some points though:
School names can change. If there is a number system available (such as NCES School ID for USA) I'd make this the PK instead.
Numbers of students must be no column in the school table; the number of students per school is implicitly given by the students related to the school.
I don't like 1:1 relations very much. Student <-> High Schooler is okay, but I'd rather have the enrollment date in the students table.
StudentID alone can't possible the PK for the grades table. It must be StudentID + Course# instead.
The line from student to course is superfluous, because the relation is given by the grades table already (which is a bridge table containing StudentID, Course# and an optional grade).
The course table's PK must not be Course# + Title, because that would mean the same course number would be allowed in combination with different titles. The PK should be the course number alone. As to the relation: I don't know if the same course can be taught at different schools. If so, the relations are correct.
Met. (though I'd break appart address into # StreetAddress, PO Box, city, state zip etc.(assuming US) Though if you want extra credit you could subtype addresses into their own table and simply have the employee, student and school addresses all in one table with a foreign key...
I'd break down Name, address just as habbit always go to
the loweest common denominator: Fname, LName, etc... (for scaling
solutions long term; combining data is easy, breaking it out later
is hard)
Looks good
Doesn't grade define Highschool? a 9th
grader is in highschool right? so why a seperate table?
4.1) now a table which lists what letters were sent to what students might be useful... but they didn't say they needed this so I'd seek clarification on the requirement.
if # is unique title doens't need to be part
of key.
Missing (you need a schoolCourses table)
Missing (I guess could be handled through your grade table though) Id call the table studentcourses and keep grade on the table... then yeah it works.
Associative/Junction table between bus/student and bus/employee
needed
Overall many-to-many need to be resolved as part of modeling. and I agree with Thorsten, I want to see all fields in all tables including the FK's and I've done enough to know the CASE tools allow it.
and while 1-1 relationships look good for 4/5th normal form. they generally are not practical anymore unless the truely represent a separate concept. So I may have a vehicle table for a vehicle database but I may also have a table for car attributes vs motorcycle attributes vs truck vs boat etc... but vehicle is the primary in this case there so little reason to separate out high school I just don't see the long term value of keeping the object separate (but maybe I just lack vision).
You'll learn that in ERD's the cardinality of the relationships between the data is THE MOST IMPORTANT (following datatype/size/scale precsion). Eliminating M-M relationships is a must. and everything really boils down to 1-M or 1-1 when your done.
Not sure what the line between the school/bus implies.... the buses are owned by the whole system... maybe you need a "System" table tie that to the schools and buses to the system. that way if you support multiple school systems you know which buses belong to what system and what schools are in what system...
How could the following database schema be drawn using E/R diagrams? (A sketch or final image would be helpful). I would also appreciate if you could guide me to a easy-to-understand tutorial on entity-relationships so I could learn how to draw them on paper first.
A CD has a title, a year of production and a CD type. (CD type could be anything: mini-CD, CD-R, CD-RW, DVD-R, DVD-RW...)
A CD usually has multiple songs on different tracks. Each song has a name, an artist and a track number. Entity set Song is considered to be weak and needs support from entity set CD.
A CD is produced by a producer which has a name and an address.
A CD may be supplied by multiple suppliers, each has a name and an address.
A customer may rent multiple CDs. Customer information such as Social Security Number (SSN), name, telephone needs to be recorded. The date and period of renting (in days) should also be recorded.
A customer may be a regular member and a VIP member. A VIP member has additional information such as the starting date of VIP status and percentage of discount.
Is this Entity diagram correct? This is so fracking confusing. I've built this diagram on just intuition rather a systematic approach they teach in a textbook. I still can't wrap my head around the many-to-one relation, weak entities, foreign keys.
There's a fair article on ERDs on Wikipedia.
When you're starting a new ERD - whether it's hand-drawn or computer-drawn - you should focus first on the entities (entity sets). Add the relationships in and then worry about fleshing out your non-key predicates. When you get some experience with ERDs you'll get to the point where you won't need much more work to achieve normalization. It will start to come naturally to you.
There are probably quite a few changes that you'll want to make to your diagram. Since this may be homework, I'll give you an alternative diagram to consider:
This model takes a more sophisticated view of your rules, for example:
Songs can appear many times on the same CD and on different CDs.
A song can be performed by multiple artists within a given track.
Producers can cooperate on a CD.
None of these are necessarily right for your model. It depends on your business rules.
Compare your model with this one and ask yourself what is different and why you might want to take one approach or the other.
take all the major concepts, draw a box for each
in the box put the name of the major concept, like SONG then an underline
under the major concept, list all the attributes like NAME
draw lines from one box to another where those concepts are linked (usually through an attribute) like line from CD to SONG
Can anyone help me to design database/table based on below criteria?
An e-commerce website is required which will allow visitors to browse, search and buy films. The following business logic applies:
Each film can be available in DVD or Blu-ray formats with different stock codes and prices. Additional formats may be added in the future by the website administrator.
Films should have a title, description, year they were released and a “star rating” out of ten stored against them.
Films are associated to none or more actor and actors can be associated to none or more films as some films may be documentaries (with no actors).
Films can be associated to one or more genre (such as action, adventure, Sci-Fi, etc).
The number of genres and actors may change so the website administrator needs to be able to add/edit as many genres and actors as they like over time.
Visitors of the website should be able to find films by browsing by actor or genre. When they do they should be able to see a list of all films that are associated to the actor/genre they have selected.
In order to buy from the website, visitors must register their details to become a user.
Users will have one or more addresses associated to their account. When they log in to the system in future all of their previously entered addresses should be available for them to select for their latest order. They should also be able to add a new address to their account at any time.
When ordering the user will select one or more items from the available films (in a particular format). They will need to select a billing and deliver address from those they have previously entered and pay for their order by credit card.
As the prices of the products can change over time the system should record what the price of each of the items in their order was at the time when they purchased as well as the total price of the entire order.
Tracking of stock levels is not required – all products can be assumed to be in stock all of the time.
If this is homework, or a class project, then you really need to start learning about normalisation. Take a look at the article on wikipedia or this introduction on the MySQL site
If this is a professional project, then you need professional help to design/develop your e-commerce site.
Here is something I could come up with, hopefully it should satisfy all the criteria mentioned in your requirements. I was designed in SQL Server as I do not have MySQL on this machine.
Steps to design the database (entity relationship modeling)
Identify the entities from the requirement. Entities are objects that hold information (usually denote real world entities like person, car, bank, employee, etc.). In your case, the entities identifiable are: Film, Actor, User, Order
Once you have identified the entities in your requirements, get down to the deciding the attributes (or properties) of the entities. The attributes are something that you associate the entity with. For example, one would identity a car by its manufacturer, model, color, engine capacity, etc. In your case, the attributes for the film entity would be Name, Genre, ActorInFilm(s), Format(s), Price
Identify the relationships between the entities. In your case, film has a relationship with actor. The relationship is: One film can have zero or more actors. And, one actor can act in one or more films. Thus film and actor are related.
Identify the cardinality of the relationships. Cardinality can be explained in simple terms as how many instance of the entity participate in the relationship.
For example, a employer can have 1 or more employees. And an employee can be employed by only one employer. In this case, there are 2 entities: Employer and Employee. They share the relationship employ. In your requirement, Film and Actor are the entities sharing the relationship Acts in (Actor(s) acts in Film). So the cardinality in this case will be one to many (Film to Actors)(one Actor can act in many Films) and zero to many (Actors to Films).
Once this part is done, you have your zero normal entity relationship diagram. Then comes the normalization. You can read about it on another post here.
After you have normalized the entity relationships (upto 3rd normal form is usually sufficient), you can implement the database design in the SQL design software (MySQL, etc.)
The best way to do the above steps is to take a sheet of paper and write the entities and attributes in a tabular format and then link them to other entities (to denote relationships).
You can refer any good book on database concepts (including normalization) or just search on google (keywords: database, normalization, database design, entity relationship modeling, etc.). What I have explained above is very brief, you will need to discover the rest of the database concepts yourself.
Entity relationship diagram is often abbreviated as ER diagram.