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important question on Entity Relationship Model(ER Model

9) Define the concept of aggregation. Give one examples of where this concept is useful.
Answer: Aggregation is an abstraction through which relationships are treated
as higher-level entities. Thus the relationship between entities A and B is treated

as if it were an entity C. Some examples of this are:
Employees work for projects. An employee working for a particular project
uses various machinery.


10) An E-R diagram can be viewed as a graph. What do the following mean in terms of the structure of an enterprise schema?
a. The graph is disconnected.
b. The graph is acyclic.

Answer : 
     a)  If a pair of entity sets are connected by a path in an E-R diagram, the entity sets are related, though perhaps indirectly. A disconnected graph implies that there are pairs of entity sets that are unrelated to each other. If we split the graph into connected components, we have, in effect, a separate database corresponding to each connected component.
    b) As indicated in the answer to the previous p…

important question on Entity Relationship Model(ER Model)

5)A university registrar’s office maintains data about the following entities: (a) courses, including number, title, credits, syllabus, and prerequisites; (b) course offerings, including course number, year, semester, section number, instructor(s), timings, and classroom; (c) students, including student-id, name, and program; and (d) instructors, including identification number, name, department, and title. Further, the enrollment of students in courses and grades awarded to students in each course they are enrolled for must be appropriately modeled.
Construct an E-R diagram for the registrar’s office. Document all assumptions that you make about the mapping constraints.
Answer: 


 In the answer given here, the main entity sets are student, course, course-offering, and instructor. The entity set course-offering is a weak entity set dependent on course. The assumptions made are :
a class meets only at one particular place and time. This E - R diagram cannot model a class meeting at differe…

important question on Entity Relationship Model(ER Model)

1) Explain the distinctions among the terms primary key, candidate key, and super key .
 Answer: 
A super key is a set of one or more attributes that, taken collectively, allows us to identify uniquely an entity in the entity set. A super key may contain extraneous attributes. If K is a super key, then so is any superset of K.A super key for which no proper subset is also a super key is called a candidate key. It is possible that several distinct sets of attributes could serve as candidate keys.The primary key is one of the candidate keys that is chosen by the database designer as the principal means of identifying entities within an entity set. 2) Construct an E-R 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.
 Answer:

3) Construct an E-R 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 …

important question on Database Management System(DBMS)

5) What are five main functions of a database administrator?
Answer: Five main functions of a database administrator are:
To create the scheme definition.To define the storage structure and access methods.To modify the scheme and/or physical organization when necessary.To grant authorization for data access.To specify integrity constraints.6)List seven programming languages that are procedural and two that are non-procedural. Which group is easier to learn and use? Explain your answer. Answer: Programming language classification:
Procedural: C, C++, Java, Basic, Fortran, Cobol, Pascal.Non-procedural: Lisp and Prolog. Note: Lisp and Prolog support some procedural constructs, but the core of both
these languages is non-procedural.
In theory, non-procedural languages are easier to learn, because they let the
programmer concentrate on what needs to be done, rather than how to do it. This is not always true in practice, especially if procedural languages are learned first.

7) List six major ste…

important question on database management system(DBMS)

1) List four significant differences between a file-processing system and a DBMS .
Answer: Some main differences between a database management system and
a file-processing system are:
Both systems contain a collection of data and a set of programs which access that data. A database management system coordinates both the physical and the logical access to the data, whereas a file-processing system coordinates only the physical access.A database management system reduces the amount of data duplication by
ensuring that a physical piece of data is available to all programs authorized to have access to it, whereas data written by one program in a file-processing system may not be readable by another program.A database management system is designed to allow flexible access to data
(i.e., queries), whereas a file-processing system is designed to allow predetermined access to data (i.e., compiled programs).A database management system is designed to coordinate multiple users
accessing the same dat…