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: Operate over existing telephone lines to carry voice, data, and video.
Explanation:
Digital subscriber line is a means of transferring high bandwidth data over a telephone line. Such data could be a voice call, graphics or video conferencing. DSL uses a user's existing land lines in a subscriber's home, allowing users to talk on a telephone line while also being connected to the Internet. In most cases, the DSL speed is a function of the distance between a user and a central station. The closer the station, the better its connectivity.
Answer
5 bits
Explanation
A bit is the least or the smallest unit of data in a computer. They are the units of information in information theory, consisting of the amount of information required to specify one of two alternatives 0 and 1. This is because A bit has a single binary value, either 0 or 1
If you use roman alphabet A to Z lets use log 2(26)=4.7 bits. when you round off it will be 5 bits.
Answer:
plug-in
Explanation:
A Plug-in is a software that provides additional functionalities to existing programs. The need for them stems from the fact that users might want additional features or functions that were not available in the original program. Digital audio, video, and web browsers use plug-ins to update the already existing programs or to display audio/video through a media file. Plug-ins save the users of the stress of having to wait till a new product with the functionality that they want is produced.
