Modelling using Entity Relationship Diagram
Granite Sales Company is one of the famous organization who is responsible for keeping the information of employees and departments they work. For each department, the department name, internal mail box number, and office phone extension are kept. A department can have many assigned employees, and each employee is assigned to only one department. Employees can be salaried employees, hourly employees, or contract employees. All employees are assigned an employee number. This is kept along with the employee’s name and address. For hourly employees, hourly wage and target weekly work hours are stored (e.g. the company may target 40 hours/week for some, 32 hours/week for others, and 20 hours/week for others).
Some salaried employees are salespeople that can earn a commission in addition to their base salary. For all salaried employees, the yearly salary amount is recorded in the system. For salespeople, their commission percentage on sales and commission percentage on profit are stored in the system. At present the management is making use of manual database, due to which many issues are being faced by the officials. So the management of Granite Sales company has decided to design Entity Relationship diagram for designing of a new database which is to be implemented in the organization.
What is an Entity Relationship Diagram?
Entity Relationship Diagram is the diagram which helps in showing the relationship among the entity sets which sets which are stored in a database. An entity is referred to as an object, and a component of data which is termed to be as a collection of similar entities. All the entities which are considered while designing of an ERD have attributes which is responsible for defining all the properties that a particular entity possess. ER diagrams are also used for designing of a sketch for the database which is to be designed. There are main two reasons for creating a database. Firstly, by either designing a new schema and secondly by documenting your existing structure which is used for storing of a data for the particular organization.
Common Entity Relationship Diagram Symbols
An ER diagram is a means of visualizing that how an information system is related. There are mainly five components of an ERD which are used for designing:
• Entities: Entities are basically represented by rectangles. It is an object or concept which helps in storing an information
• Actions: Action is mostly represented by diamond shape and helps in showing how the two entities share within the database that is designed.
• Attributes: Attributes are basically represented by ovals. As a key attribute is the unique distinguishing characteristics of the entity. Along with this it is also stated that a multivalued attribute can have more than one value.
• Connection lines: Connection lines are solid lines which are responsible for connecting the attributes to show the relationship among all the entities which are present in the diagram.
• Cardinality: Cardinality helps in specifying that how many instances of an entity are related to one instance of another entity. Ordinality is closely linked to cardinality which helps in describing that whether the relationship is mandatory or optional.