For the view of Exercise 4.18, explain why the database system would not allow a tuple to be inserted into the database through this view.
For reference
For the database of Figure 4.12, write a query to find the ID of each employee with no manager. Note that an employee may simply have no manager listed or may have a null manager. Write your query using an outer join and then write it again using no outer join at all.
OUTER JOIN
select e.ID from employee e left outer join manages m on e.ID = m.ID
where m.manager_id is null;
NO OUTER
select e.ID from employee e where e.ID not in (select m.ID from manages m) or e.ID in (select m.ID from manages m where m.manager_id is null);
Answer:
True
Explanation:
in function guess:- a = x; b = y; c = z
so 45 > 31 AND 45 < 38
since both the stements are true
True is printed
Attackers frequently use ACK scans to circumvent a firewall or other filtering tools. During a NULL scan, all packet flags are enabled. The most recent versions of Nessus Server and Client are compatible with Windows, Mac OS X, FreeBSD, and the vast majority of Linux variants.
<h3>What is ack scan ?</h3>
- ACK scans are used to identify hosts or ports that have been blocked or are resistant to other types of scanning. An attacker uses TCP ACK segments to learn about firewall or ACL configuration.
- Attackers probe our router or send unsolicited SYN, ACK, and FIN requests to specific UDP/TCP ports.
- TCP ACK Scan sends an ACK message to the target port to determine whether or not it is filtered.
- On unfiltered ports, a RST reply packet will be sent for both open and closed ports. Filtered ports will either generate no response or generate an ICMP reply packet with an unreachable destination.
- The TCP ACK scanning technique attempts to determine whether a port is filtered by using packets with the ACK flag set.
To learn more about ask scan refer to:
brainly.com/question/13055134
#SPJ4
D. DoS. DoS is a way to potentially lag or even crash different types of servers ranging from as small as a simple website to bigger websites and video games servers.
Hypertext Markup Language, a standardized system for tagging text files to achieve font, colour, graphic, and hyperlink effects on World Wide Web pages.
this information was taken from google
