ERD diagram


DRAW ERD FOR THE FOLLOWING
Question 1
A publishing company produces scientific books on various subjects. The books are written by authors who specialize in one particular subject. The company employs editors who, not necessarily being specialists in a particular area, each take sole responsibility for editing one or more publications. A publication covers essentially one of the Specialist Subjects and is normally written by a single author. When writing a particular book, each author works with on editor, but may submit another work for publication to be Supervised by other editors. To improve their competitiveness, the company tries to employ a variety of authors, more than one author being a specialist in a particular subject.
Question 2
A general hospital consists of a number of specialized wards (such as Maternity, Paediatry, Oncology, etc). Each ward hosts a number of patients, who were admitted on the recommendation of their own GP and Confirmed by a consultant employed by the Hospital. On admission, the personal details of every patient are recorded. A separate register is to be held to store the information of the tests undertaken and the results of a prescribed treatment. A number of tests may be conducted for each patient. Each patient is assigned to one leading Consultant but may be examined by another doctor, if required. Doctors are specialists in some branch of medicine and may be leading consultants for a number of patients, not necessarily from the same ward.
Question 3
A database is to be designed for a Car Rental Co. (CRC). The information required includes a description of Cars, Subcontractors (i.e., garages), company expenditures, Company revenues and customers. Cars are to be described by such data as make, model, year of production, and engine size, and fuel type, number of passengers, registration number, purchase price, purchase date, rent price and insurance details. It is the company policy not to keep any car for a period exceeding one year. All major repairs and maintenance are done by Subcontractors (i.e., franchised garages), with whom CRC has long-term agreements. Therefore the data about garages to be kept in the database includes garage names, addresses, range of Services and the like. Some garages require payments immediately after a repair has been made, with others CRC has made arrangements for Credit facilities. Company expenditures are to be registered for all outgoings connected with purchases, repairs, maintenance, insurance etc. Similarly, the cash inflow coming from all Sources – Car hire, car sales, insurance claims – must be kept of file. CRC maintains reasonably stable client base. For this privileged category of customers special credit card facilities are provided. These customers may also book in advance a particular car. These reservations can be made for any period of time up to one month. Casual Customers must pay a deposit for an estimated time of rental, unless they wish to pay by Credit card. All major credit cards care accepted. Personal details (such as name, address, telephone number, driving license number) about each customer are kept in the database.
Question 4
A database is to be designed for a college to monitor students’ progress throughout their Course of study. The students are reading for a degree (such as BA, BA (Hons) MSc, etc.) within the framework of the modular system. The college provides a number of module, each being characterized by its Code, title, Credit value, module leader, teaching staff and the department they come from. A module is co-ordinated by a module leader who shares teaching duties with one or more lecturers. A lecturer may teach (and be a module leader for) more than one module. Students are free to choose any module they wish but the following rules must be observed some modules require pre-requisites modules and some degree programmes have compulsory modules. The database is also to contain some information about students including their numbers, names, addresses, degrees they read for and their past performance (i.e., modules taken and examination results).
Question 5
A relational database is to be designed for a medium sized company dealing with industrial applications of Computers. The Company delivers various products to its customers ranging from a single application program through to complete installation of hardware with Customized software. The company employs various experts, Consultants and Supporting staff. All personnel are employed on long-term basis, i.e., there are no short-term or temporary staffs. Although the Company is somehow structured for administrative purposes (that is, it is divided into departments headed by department managers) all projects are carried out in an inter-disciplinary way. For each project a project team is selected, grouping employees from different departments and a project manager (also an employee of the company) is appointed who is entirely and exclusively responsible for the control of the project, quite independently of the company’s hierarchy. The following is a brief Statement of Some facts and policies adopted by the company.
Question 6
Explain the distinctions among the terms primary key, candidate key, and Superkey :
  • A superkey is any set of attributes such that the values of the attributes (taken together) uniquely identify one entity in the entity set.
  • A candidate key is a minimal superkey – a superkey with no redundant attributes. In other Words, if any one of the attributes is removed, the set of attributes that remain no longer form a superkey.
  • A primary key is one of the candidate keys, designated by the database designer.
  • Every primary key is also a candidate key; every candidate key is also a superkey, but not vice Versa.

Construct an ER diagram for a car-insurance company whose customers own one or more cars each. Each car has associated with it zero to any number of recorded accidents

Construct an ER diagram for a hospital with a set of patients and a set of medical doctors. Associate with each patient a log of the various tests and examinations conducted.

Construct an E-R diagram for the registrar’s office. Document all assumptions you make about the mapping Constraints.
Assumptions:
  • A class meets only at one particular place and time. This diagram does not attempt to model a class meeting at different places or at different times
  • There is no guarantee that the database does not have two classes meeting at the sameplace and time
  • Each class has a unique instructor


Consider a database used to record the marks that students get in different exams of different course offerings.
 (a) Construct an ER diagram for the database modeling exams as entities and using a ternary relationship

(b) Construct an alternative ER diagram that uses only a binary relationship between students and course-offerings. Make sure that only one relationship exists between a particular student and course-offering pair, yet you can represent the marks that a student gets in different exams of a course offering


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