One very important topic in this lesson is the concept of an entity. Identifying entities is one of the first tasks a system needs to do
In any system there are two types of entities: external entities are the offices, people, departments, or users that interact with the system. Internal entities, or just entities, are the things that the system must store data (attributes) about. Identifying the entities, both internal and external, is a first task, because these entities will be used throughout the systems analysis and design process.
In a college registration system, the most important entities (internal entities) are students, professors, courses, sections, and rooms. Each of those entities has attributes (data). A student has attributes of name, id, major, address, email, and more. A course has a name, credits, description, and 0 or more prerequisites. A room probably has capacity, and 0 or more types of equipment. A section has an id, date time, room, and instructor.
On a credit card statement, the entities are the customer, the statement, and 0 or more transactions. The statement has a billing date, due date, amount, minimum payment due and 0 or more transactions. Each transaction has date and time, a reference number, the merchant and the amount.
Transactions can include purchases, interest charged, and payments. By using a more general term, transaction, we avoid having to specify each type of transaction. Also that means that all of the transactions can be sorted by date.
Similarly, our address book has friends, family, doctors, and many others. By using the more inclusive term contacts, we can sort them into alphabetical order.
Exercise: Look at some of the bills and receipts that you have. Try to identify the entities and the attributes of each entity.
In a college registration system, there are entities such as Student, Professor, Course, Section, and Room. In a store the common entities are Customer, Product, Supplier, and Salesperson.
Entities and Attributes: Introduction