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The Entity Relationship Diagram
The Entity Relationship Diagram is a specialized graph that shows the relationships between the entities in the database. ER diagrams use symbols to represent three types of information: entities (or concepts), relationships, and attributes.
About the relationship diagrams between the entity
In industry-standard ER diagrams, rectangles or squares are entities, which are tables that contain specific information in a database. Diamonds represent relationships, which are the interactions between entities. Charts represent attributes, which are data that describe the entity.
Although entity-relationship diagrams may seem complex, these diagrams help knowledgeable users to understand database structures at a high level without the need to attach details.
Database designers use ER diagrams to design relationships between database entities in a clear format. Many software packages contain automatic methods for creating ER diagrams from existing databases. (A. Elfaki, 2019)
Entities Are the Objects that Are Tracked
Every object tracked in a database is an entity, and every entity is a table in a relational database. Usually, each entity in a database corresponds to a single row.
If the database contains the names of people, then their entity might be called the name of the person. There will be a table with the same name in the database, and everyone will be assigned a row in the People table. (A. Latif, 2008)
Entity Description Attributes
Databases contain information about each entity. This information is referred to as features. Attributes consist of unique information for each listed entity. In the example of a person, attributes could include first name, last name, date of birth, and identification number.
Attributes provide detailed information about the entity. In a relational database, the attributes are preserved in the fields in which the information within the record is preserved. The database is not limited to a specific number of features. (B. R. Sinha, 2013)
Relationships Hold the Data Together
The value of the Entity-Relationship Diagram lies in its ability to display information about relationships between entities. In the example, information about the city each person lives in could be tracked. Information about the city itself can also be tracked into a city entity with a relationship that connects people and city information.
There are three types of entity relationships:
- One-to-One: Sometimes, one entity is related to one other entity. For example, every employee in the database has only one Social Security number, and the number is unique.
- One-to-Many: A single entity may also be related to several other entities. For example, there is a relationship between one office of the subsidiary company and all the employees working in that branch. (B. R. Sinha, 2013)
- Many-to-many: Multiple entities may be associated with multiple other entities. For example, a company might manufacture three products and have a sales team working to sell those products. Some sales personnel may divide their time between products.
- Each project will have one or more Project Manager, consultants and contractors.
- Each project will have many skills needed to complete the project.
- The project will have many members working on its referred staffing, including Managers, consultants and contractors.
- Each project will have one client associated with it.
- Each project will have a client-side deputy responsible for decision making needed in the project.
- Each project will have a client-side contact person responsible for the proper day to day communication with the client.
- The consultant has one too many skills, and having a skill is mandatory.
- Staffing will have many consultants working on a project, including the project manager. (B. R. Sinha, 2013)
Entities and Relations
This entity will have basic to detailed information about projects; this is the central entity and has primary key Project ID, which will be unique and auto-generated. Other attributes are project name, description of the project, project manager referred from staffing entity, start date, total budget, cost till the current date, status of project as tracking statement, client referred from client entity, skill set required to accomplish this project referred from skill entity. (A. Pipitone, 2016)
This entity will hold information related to skills having a primary key as Skill ID which will be unique and auto-generated. Other fields are Skill Name and Description of skill, specifying detailed information of skill. In a consultant entity a consultant can hold one too many skills, also a project can have many skills needed to accomplish the project. (Rocha, 2018)
This entity have consultant Id as the primary key which is unique and will be auto-generated. Other fields are first name, last name, home phone number, mobile number, email address, date commenced or joining date, date of birth, street address, postcode or zip code, job description weather this consultant is manager, contractor or other staff member specified by job description.
This entity contains information about staff working on a project, having staff id as primary key and is unique. Other fields are Assign Date on which date a staff member is assign to a project, Completion date of staff member for a specific project, Hours worked by a staff member on a specific project. Designation of staff member weather he/she’s working on project as manager, consultant or a contractor. Staffing entity is connected with consultant entity which has detail information about staff members assign to a project and each staff member’s skill is in skill entity. (B. R. Sinha, 2013)
This entity is for client related information and connects project with client, having Client ID as primary key and is auto generated. Other fields are Company name for which project is, Street address of company, Post code, Company Phone number, Contact person name this person will be responsible for communication between companies, contact person name, duty in this entity is a person responsible for handling decision making related to a project, duty’s email and phone is also included in this entity. This entity is connected with project, as one client can have one to many projects. (A. Pipitone, 2016)
Database System Task List:
Task the Database Will Perform:
- Enter and store project information, status of project and costing of project.
- Enter and store detail about project like description client and staff members.
- Enter and store client related data address and phone numbers
- Enter and store Client side contact person’s name, phone etc.
- Enter and store the details of specific skilled worker and outer resources
- Enter and store Duty related information responsible for decision making in a specific project.
- Enter and different skill available to company and needed for a project.
- Enter and store information related to staff members including joining date, designations and assigned projects.
- Enter and store staffing information working on a project.
Question the Database Will Answer:
- The base gives an idea about the budget of project and costing of project.
- Who is managing a project?
- Who is the client for whom the project is being done?
- What are the requirements and milestones and relation between different projects being completed?
- Number of project and details about project a client has.
- It gives the number of staff members working on a specific project.
- It also gives the number of working hours of the employees working on a specific project
- Who is/was the contact person for a project?(A. Latif, 2008)
- Who is the deputy of a project responsible for decision making?
- It gives the list of skills required in order to complete a specific project.
- It also gives the details of staff members who are free or doing work on a project.
- It gives the progress report of the project if the milestones are completed successfully or not.
- Status of a project is in development or completed etc.
- Give the list of staff member who will get free next month and available for other projects.(A. Pipitone, 2016)
- Give the staff member having most worked hour on a specific project.
- Give how many projects a client has.
- Give the project details and skill needed to complete and process to complete the project
- It also gives the number of staff members required to work on a given project in order to meet the deadline for the project.
- It also tells about the staff members who have worked on different projects for a specific client already.
- Staff members with some specific skill required to complete few specific duties are also given(Rocha, 2018)
- It also gives the details of clients having most projects in progress.
Elfaki, A. A. (2019). Mapping ERD to Knowledge Graph. IEEE World Congress on Services (SERVICES), (pp. 110-114). Milan.
Latif, M. Y. ( 2008). Semi-automated approach for converting ERD to semi-star schema. 4th International Conference on Emerging Technologies, (pp. 264-268). Rawalpind.
Pipitone, F. A. (2016). An Innovative Statistical Tool for Automatic OWL-ERD Alignment. IEEE Tenth International Conference on Semantic Computing (ICSC), (pp. 96-99). Laguna Hills.
- Sinha, P. P. (2013). Database modeling with Object Relationship Schema. 12th International Conference on Information Technology Based Higher Education and Training (ITHET), (pp. 1-7). Antalya.
Rocha, A. D. (2018). Automatic evaluation of ERD in e-learning environments. Iberian Conference on Information Systems and Technologies (CISTI), (pp. 1-5). Caceres.