Creating ER Diagram Representation in DBMS | Studytonight
For example, Roll_No, Name, DOB, Age, Address, Mobile_No are the attributes which defines entity type Student. In ER diagram, attribute is represented by an. An entity-relationship (ER) diagram is a graphical representation of entities and their For example, in a database of employees, each employee name (A) is. What is the ER Model? The ER or (Entity Relational Model) is a high-level conceptual data model diagram. Entity-Relation model is based on.
You are attending this lecture I am giving the lecture Just loke entities, we can classify relationships according to relationship-types: A student attends a lecture A lecturer is giving a lecture. Weak Entities A weak entity is a type of entity which doesn't have its key attribute.
It can be identified uniquely by considering the primary key of another entity. For that, weak entity sets need to have participation.
ER Model Basic Concepts
Let's learn more about a weak entity by comparing it with a Strong Entity Strong Entity Set Strong entity set always has a primary key. It does not have enough attributes to build a primary key.Introduction to ER model
It is represented by a rectangle symbol. It is represented by a double rectangle symbol. It contains a Primary key represented by the underline symbol. It contains a Partial Key which is represented by a dashed underline symbol.
The member of a strong entity set is called as dominant entity set. The member of a weak entity set called as a subordinate entity set.
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Primary Key is one of its attributes which helps to identify its member. In a weak entity set, it is a combination of primary key and partial key of the strong entity set. In the ER diagram the relationship between two strong entity set shown by using a diamond symbol. The relationship between one strong and a weak entity set shown by using the double diamond symbol.
The connecting line of the strong entity set with the relationship is single.
The line connecting the weak entity set for identifying relationship is double. Attributes It is a single-valued property of either an entity-type or a relationship-type. For example, a lecture might have attributes: An attribute is represented by an Ellipse Types of Attributes Description Simple attribute Simple attributes can't be divided any further.
For example, a student's contact number. For example, you might create a playlist of your favorite tracks from an artist. Track ratings, to record your opinion on how good a track is.
Source details, such as when you bought an album, what media it came on, how much you paid, and so on. Album details, such as when and where it was recorded, the producer and label, the band members or sidemen who played on the album, and even its artwork.
Smarter track management, such as modeling that allows the same track to appear on many albums. The University Database The university database stores details about university students, courses, the semester a student took a particular course and his mark and grade if he completed itand what degree program each student is enrolled in.
We explain the requirements next and discuss their shortcomings at the end of this section. Consider the following requirements list: The university offers one or more programs. A program is made up of one or more courses. A student must enroll in a program. A student takes the courses that are part of her program. A program has a name, a program identifier, the total credit points required to graduate, and the year it commenced.
A course has a name, a course identifier, a credit point value, and the year it commenced. Students have one or more given names, a surname, a student identifier, a date of birth, and the year they first enrolled. When he finishes the course, a grade such as A or B and a mark such as 60 percent are recorded. Each course in a program is sequenced into a year for example, year 1 and a semester for example, semester 1.
Although it is compact, the diagram uses some advanced features, including relationships that have attributes and two many-to-many relationships. The ER diagram of the university database In our design: Each student must be enrolled in a program, so the Student entity participates totally in the many-to-one EnrollsIn relationship with Program.
A program can exist without having any enrolled students, so it participates partially in this relationship. As a weak entity, Course participates totally in the many-to-one identifying relationship with its owning Program. This relationship has Year and Semester attributes that identify its sequence position. Student and Course are related through the many-to-many Attempts relationships; a course can exist without a student, and a student can be enrolled without attempting any courses, so the participation is not total.
When a student attempts a course, there are attributes to capture the Year and Semester, and the Mark and Grade. For a real university, many more aspects would need to be captured by the database. The airline has one or more airplanes. An airplane has a model number, a unique registration number, and the capacity to take one or more passengers.
ER Diagram Tutorial in DBMS (with Example)
An airplane flight has a unique flight number, a departure airport, a destination airport, a departure date and time, and an arrival date and time. Each flight is carried out by a single airplane. A passenger has given names, a surname, and a unique email address.
A passenger can book a seat on a flight. The ER diagram of the flight database An Airplane is uniquely identified by its RegistrationNumber, so we use this as the primary key. A Flight is uniquely identified by its FlightNumber, so we use the flight number as the primary key.
The departure and destination airports are captured in the From and To attributes, and we have separate attributes for the departure and arrival date and time. Because no two passengers will share an email address, we can use the EmailAddress as the primary key for the Passenger entity. An airplane can be involved in any number of flights, while each flight uses exactly one airplane, so the Flies relationship between the Airplane and Flight relationships has cardinality 1: N; because a flight cannot exist without an airplane, the Flight entity participates totally in this relationship.
A passenger can book any number of flights, while a flight can be booked by any number of passengers.