stillproud.org215 house Data Modeling ERD entities Relationships features Example software program Lab Assignment MySQL Account

Data Modeling

Data modeling is a method to record a software system using diagrams and symbols. It is provided to represent interaction of data.

The greatest level of abstraction because that the data version is dubbed the Entity relationship Diagram (ERD). The is a graphical representation of data needs for a database.

You are watching: What is a technique for documenting the entities and relationships in a database environment?

Entity relationship Diagram

The main value of very closely constructing an ERD is that it can readily be converted into a database structure.

There are three materials in ERD.

Entities: variety of tables you require for her database. Attributes: information such together property, truth you require to explain each table. Relationships: just how tables are linked together.


Entities space the simple objects of ERDs. These room the tables of her database. Entity space nouns and also the varieties usually loss into 5 classes: concepts, locations, roles, events or things. for example: students, courses, books, campus, employees, payment, projects. A particular example that an reality is referred to as an instance. Each instance becomes a record or a heat in a table. For example: the student john Smith is a document in a table called students.


Relationships space the associations between the entities. Verb often describe relationships between entities. We will use Crow"s Foot signs to stand for the relationships. Three varieties of relationship are discussed in this lab. If you review or listen cardinality ratios, it also refers to species of relationships.


One to One partnership (1:1)

A single entity instance in one entity class is concerned a solitary entity circumstances in an additional entity class.

because that example: Each student fills one seat and also one seat is assigned to just one student. each professor has one office space. One to many Relationship (1:M)

A solitary entity instance in one entity course (parent) is concerned multiple reality instances in another entity class (child)

because that example: One instructor have the right to teach many courses, yet one course have the right to only be taught by one instructor. One instructor might teach plenty of students in one class, however all the students have actually one instructor for the class. numerous to many Relationship (M:M)

Each entity instance in one entity course is related to multiple entity instances in one more entity class; and vice versa.

because that example: every student deserve to take plenty of classes, and also each class can it is in taken by countless students. Each customer can buy numerous products, and also each product can be purchase by countless consumers.

The detailed Crow"s Foot partnership symbols can be discovered here. Crow"s Foot partnership Symbols

Many to numerous relationships are difficult to represent. We have to decompose a numerous to numerous (M:M) relationship right into two one-to-many (1:M) relationships.


Attributes are facts or summary of entities. Lock are also often nouns and also become the columns the the table. Because that example, for reality student, the can be very first name, last name, email, attend to and phone call numbers.

Primary an essential

Primary Key* or id is an attribute or a collection of attributes that uniquely identifies an instance of the entity. For example, for a student entity, college student number is the primary key since no 2 students have actually the very same student number. We can have just one primary an essential in a table. It determine uniquely every row and it can not be null. Foreign vital A international key+ (sometimes called a to express key) is a crucial used to connect two tables together. Commonly you take the primary vital field native one table and insert it right into the various other table where it becomes a foreign crucial (it remains a primary vital in the initial table). We deserve to have more than one foreign vital in a table.

An Example

Here"s a sample crowsfoot diagram native a previous offering the stillproud.org270 taught right here at the college of Regina. We"ve redrawn the diagrams utilizing more modern diagramming tools, however the content is unchanged. It supplies a most ERD symbols, for this reason you can want to usage Vivek Chawla"s fast guide if you check out it.


Quick Questions

How numerous entities room there in this diagram and what are they? over there are 7 entities: STUDENT, COURSE, INSTRUCTOR, SEAT, CLASS, SECTION and also PROFESSOR. What are the for reality STUDENT? The qualities for entity STUDENT are: student_id, student_name and student_address What is the primary vital for STUDENT? The primary vital for college student is: student_id What is the primary crucial for COURSE? not a trick question! there is just one major key, however it is made up of 2 attributes. This is called a compound key
. What foreign keys do STUDENT and COURSE contain? STUDENT and also COURSE save on computer no international keys in this diagram. This could suggest that there are troubles with the design... Amongst them is the plenty of to numerous relationship here. This usually calls for that we create a separate table to define the relationship. This form of table generally connects foreign ids to each other. In this case, let"s add an entity dubbed REGISTRATION in the middle of the "takes" relationship. Since students probably sit in different seats because that each course they room registered in, allows relate chair to REGISTRATON instead of STUDENT:
The it is registered entity likewise uses a special instance of compound crucial that has compound international keys - that is a composite key
. .

ERD Tools

plenty of tools are accessible to assist you design Entity relationship Diagrams. Here is a short list of alternatives you might want come try. Visio ConceptDraw when web page is loaded, make sure to choose Entity Relation ~ above the left hand side. If you space lucky your lab instructor will execute a demonstration... ;) come submit her completed ERD, violin it come PDF favor this: File->Export as->PDF...

rap Assignment


Create an ideal Entity partnership Diagram (ERD) for the data linked with an virtual application. This ERD should encompass the user accounts, posts and re-posts entities. To obtain you started, you deserve to follow the instance given below.


User reality

The User entity collect attributes: user_id(*primary key), user_email, user_name, user_password user_DOB, User_image and etc.

short article entity

The article entity collect attributes: post_id(*primary key), user_id (+foreign key), post_detail, post_date, URL and etc.

Re-post reality

What should Re-post entity contain? Think of one or more things a repost can add to a post. Justification your design with a label.


The relationship shown in between user and also post in our example is great enough. Add relationships in between Re-post and the other two. Justify or explain your decision in text labels, and be sure you have selected compatible primary and foreign keys. For example: A user might make numerous posts, yet each post was composed by just one user. We might search because that the user_id in the articles to find all the articles a user made.

Please violin the document as a PDF document.

Upload the ERD top top URcourses and carry out a working link to the ERD from her homepage prior to 11:55pm top top the day you take it this lab.

Be prepared for following lab, acquire your MySQL account set up.

Marks will be deducted if her MySQL account is not prepared by next lab.

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Creating a MySQL Account

For storing documents or data sets, the stillproud.org215 labs use Hercules to work-related with a MySQL database. The following provides accuse to develop your very first MySQL database account.

click on the "MySQL" attach


enter your username/ password (the Titan password you use for this class), climate click Login


If girlfriend don"t have actually a database yet, please check out the rules, expropriate the policy and also click Process
. Choose your MySQL password (must be different from your password), climate click produce Please do a keep in mind (on her phone or otherwise) that this password because you will be utilizing it in a later on lab. If an account currently exists, you deserve to reset her password or drop her database


the takes 5 to 30 minute to produce a MySQL database.

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