What update anomalies occur in the EMP_PROJ and EMP_DEPT relations of Figure 15.3 and 15.4?
What will be an ideal response?
In EMP_PROJ, the partial dependencies {SSN}->{ENAME} and {PNUMBER}->{PNAME,
PLOCATION} can cause anomalies. For example, if a PROJECT temporarily has no
EMPLOYEEs working on it, its information (PNAME, PNUMBER, PLOCATION) will not be
represented in the database when the last EMPLOYEE working on it is removed (deletion
anomaly). A new PROJECT cannot be added unless at least one EMPLOYEE is assigned to
work on it (insertion anomaly). Inserting a new tuple relating an existing EMPLOYEE to
an existing PROJECT requires checking both partial dependencies; for example, if a
different value is entered for PLOCATION than those values in other tuples with the same
value for PNUMBER, we get an update anomaly. Similar comments apply to EMPLOYEE
information. The reason is that EMP_PROJ represents the relationship between
EMPLOYEEs and PROJECTs, and at the same time represents information concerning
EMPLOYEE and PROJECT entities.
In EMP_DEPT, the transitive dependency {SSN}->{DNUMBER}->{DNAME, DMGRSSN}
can cause anomalies. For example, if a DEPARTMENT temporarily has no EMPLOYEEs
working for it, its information (DNAME, DNUMBER, DMGRSSN) will not be represented
in the database when the last EMPLOYEE working on it is removed (deletion anomaly). A
new DEPARTMENT cannot be added unless at least one EMPLOYEE is assigned to work on it
(insertion anomaly). Inserting a new tuple relating a new EMPLOYEE to an existing
DEPARTMENT requires checking the transitive dependencies; for example, if a different
value is entered for DMGRSSN than those values in other tuples with the same value for
DNUMBER, we get an update anomaly. The reason is that EMP_DEPT represents the
relationship between EMPLOYEEs and DEPARTMENTs, and at the same time represents
information concerning EMPLOYEE and DEPARTMENT entities.
You might also like to view...
Write a program that reads a value of k from the keyboard and displays the value of M(k), which is computed by a recursive method.
Suppose we have a satellite in orbit. To communicate to the satellite, we can send messages composed of two signals: dot and dash. Dot takes 2 microseconds to send, and dash takes 3 microseconds to send. Imagine that we want to know the number of different messages, M(k), that can be sent in k microseconds. • If k is 0 or 1, we can send 1 message (the empty message). • If k is 2 or 3, we can send 1 message (dot or dash, respectively). • If k is larger than 3, we know that the message can start with either dot or dash. If the message starts with dot, the number of possible messages is M(k - 2). If the message starts with dash, the number of possible messages is M(k - 3). Therefore the number of messages that can be sent in k microseconds is M(k - 2) + M(k - 3).
When saving a PowerPoint template, the ________ file extension is used
A) .pttx B) .potx C) .pptx D) .pptp
The part of the Print Preview window that indicates the page displayed and the total number of pages is the ________
Fill in the blank(s) with correct word
Which of the following best describes business impact analysis?
A. Evaluates risks to the organization and prioritizes the systems that will be used for recovery B. Describes the critical processes, procedures, and personnel that must be protected in an event of an emergency C. Describes the exact steps and procedures that should be followed to recover critical business systems in the event of a disaster D. Determines the cost of continuous operation and the value of each service