Entity Relationship Modeling Examples - Learning MySQL [Book]
DBMS. • Entity-Relationship model is used in the conceptual design of a database Examples are a person, car, customer, product, gene, book etc. • Attributes: an A superkey of an entity type is a set of one or more attributes whose values. Let's take an example of a company database The lines connecting an entity with a relationship whether single or double line refer to another. What are the entities and relationships in the enterprise? – What information What are the integrity constraints or business rules that hold? .. Binary vs. Ternary Relationships (Contd.) y Previous example illustrated a case when 2 binary.
Get unlimited access to videos, live online training, learning paths, books, tutorials, and more. No credit card required Entity Relationship Modeling Examples Earlier in this chapter, we showed you how to design a database and understand an Entity Relationship ER diagram.
This section explains the requirements for our three example databases—music, university, and flight—and shows you their Entity Relationship diagrams: The music database is designed to store details of a music collection, including the albums in the collection, the artists who made them, the tracks on the albums, and when each track was last played.
The university database captures the details of students, courses, and grades for a university. The flight database stores an airline timetable of flight routes, times, and the plane types. The next section explains these databases, each with its ER diagram and an explanation of the motivation for its design. The Music Database The music database stores details of a personal music library, and could be used to manage your MP3, CD, or vinyl collection.
It ignores the requirements of many music genres, making it most useful for storing popular music and less useful for storing jazz or classical music. The collection consists of albums. An album is made by exactly one artist. An artist makes one or more albums. An album contains one or more tracks Artists, albums, and tracks each have a name.
Each track is on exactly one album. Each track has a time length, measured in seconds. When a track is played, the date and time the playback began to the nearest second should be recorded; this is used for reporting when a track was last played, as well as the number of times music by an artist, from an album, or a track has been played.
Conversely, each play is associated with one track, a track is on one album, and an album is by one artist. The attributes are straightforward: The track entity has a time attribute to store the duration, and the played entity has a timestamp to store when the track was played. If you wanted to use the music database in practice, then you might consider adding the following features: Support for compilations or various-artists albums, where each track may be by a different artist and may then have its own associated album-like details such as a recording date and time.
Under this model, the album would be a strong entity, with many-to-many relationships between artists and albums. Playlists, a user-controlled collection of tracks.strong entity vs weak entity in dbms
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.
Difference Between Entity and Relationship in DBMS
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. Refer the below diagram. They are also called strong entities as they do not depend on other entities. The Lecturer entity has attributes id, name, and specialty.
The Student entity has the id and name attribute. The Exam entity depends on the Course Entity. Therefore, Exam is a weak entity.
Difference Between Entity and Relationship in DBMS - junkgenie.info
There are three types of relationships that can exist between the entities. They are the binary, recursive and the ternary relationship. It is further classified into three types. They are one to one relationship 1: When one instance of an entity is associated with one instance of another type of entity, it is called one to one 1: There is one Head of the Department to manage the department.
So, it is a one to one relationship. When one instance of an entity is associated with many instances of another type of entity, it is called one to many 1: In a faculty, there can be multiple students, but a single student is in one faculty.
Therefore, it is a one to many 1: When many instances of an entity are associated with many instances of another type of entity, it is called many to many m: A student can participate in multiple courses, and a single course can have multiple students.
So, it is a many to many relationship m: Furthermore, when an entity is related to itself, it is called a recursive relationship. When there are three entities connected, that relationship is known as a ternary relationship.
Learning MySQL by Hugh E. Williams, Saied M.M. Tahaghoghi
In the above ER diagram, the Lecture conducts Course. A single Lecturer can conduct multiple Courses, but one Course is conducted by one Lecturer.
So, it is a one to many 1: